Thyroid Hair Loss: Why There Is Often More Than One Cause
Your brush is full, even though your thyroid is being treated. Often, several links interlock: the hormone, your iron stores and the conversion of T4 into T3. Here you can read how this chain may fit together and where you can start.
All guides in the thyroid cluster
Hair is a measuring instrument with a delay. What lands in your brush today often began weeks or months ago. If you want to start at the root, you need to read the chain behind it, not just its last link.
“My thyroid is supposed to be well controlled. So why is my hair still falling out?”
I know this pattern very well. A woman has been living with Hashimoto's for years and takes her levothyroxine every morning. At every check, her TSH is within the target range.
She had already been through several shampoos, a hair tonic and a biotin capsule. Looking through her results together, one gap stood out. Her ferritin, meaning her iron stores, had barely been measured for years. The last value was just above the lab's lower limit. For a long time, she had considered her heavy periods normal.
The turning point was a different question. No longer: What goes on the scalp? But instead: Which link in the chain is missing? Her iron stores were refilled under medical supervision, and a gynecologist looked into the cause of the blood loss. Her thyroid treatment stayed unchanged, in the hands of the practice already treating her.
A few months later, she told me that there was noticeably less hair in her brush. Short new hairs were appearing along her part.
I cannot claim causation, but I document the temporal relationship. Diffuse hair loss can also ease on its own, and more than one factor changed during this period. A single course says nothing about you.
The lesson: A well-managed thyroid is one prerequisite for strong hair. But it is not the only one.
Maybe you recognize yourself in this. You have compared photos, studied your part in the mirror and counted hairs in the sink. And at some point, you heard the sentence: Your thyroid is well controlled.
That may be true. Your hair can still keep falling out. That is not a contradiction, and you are not imagining it. Hair hangs on several threads at once, and the thyroid is only one of them.
Many people are quick to link hair loss with vanity. I see it differently. When you empty your brush every morning, you lose more than hair. You lose a piece of trust in your own body.
Hair loss with a treated thyroid is often not the problem of a single value. Hormone, iron stores, the conversion of T4 to T3 and the immune system can interlock like links in a chain.
This article takes you through this chain, link by link. How telogen effluvium develops. What thyroid hormones do directly in the hair root. Why your iron stores are so often involved, and what the conversion of T4 to T3 has to do with it. At the end, you will find three steps you can take into your next doctor's appointment.
I have covered the question of which ferritin level is enough for your hair in detail in Iron deficiency and hair loss. Here, the focus is on how it interacts with the thyroid.
What you will learn in this article
- Why hair falls out only months later
- What T3 and T4 do directly in the hair root
- Why a normal ferritin can be on the low side for hair
- How thyroid and iron can slow each other down
- What the conversion of T4 to T3 has to do with it
- Zinc and selenium: too little and too much
- Hashimoto's and alopecia areata
- Whether levothyroxine itself can cost you hair
- Stress as the fourth lens
- Three steps for your next doctor's appointment
Why does hair fall out only months later?
The moment you notice it is rarely the moment it begins. That is exactly what makes hair loss so confusing. You look for the cause in the past week and find nothing.
Hair loss is usually an echo. Today, it shows you what your hair roots went through weeks or months ago.
Every hair lives in its own rhythm. Imagine your head as a large garden where the plants never all bloom at once. Most of them are growing right now. A small share is taking a break. And a few hairs say goodbye every day, so that a new one can grow back in the same spot. Ralf Paus and George Cotsarelis described this cycle of growth, transition and rest in the New England Journal of Medicine in 1999 as a foundation of hair biology.
Growth
The cells of the hair root divide without pause. For scalp hair, this phase normally lasts several years. This is where length comes from.
Transition
The root stops production and pulls back. A short transition of a few weeks.
Rest
The hair now sits only loosely in the skin as a club hair. After a few months, it falls out, often because a new hair is already pushing up underneath.
In telogen effluvium, the most common cause of diffuse hair loss in women, this rhythm gets thrown off. A trigger sends many hairs into the resting phase at once. But they do not fall out right away. They wait until their resting time is over.
In 2009, the Delhi dermatologist Shyam Behari Shrivastava summarized how diffuse hair loss in women can be classified.
A sudden increase in shedding two to three months after a trigger, such as giving birth, a high fever or major surgery, is typical of telogen effluvium. According to the review, every case of diffuse hair loss without an obvious cause should include ferritin as well as T3, T4 and TSH, in addition to a blood count and urinalysis. Iron deficiency and thyroid disorders are described as the two common companions, and they usually show no outward signs. Once the trigger is gone or treated, telogen effluvium usually subsides within three to six months, according to the paper.
What this means for you: Don't look for the cause in the past week, but in the months before. And have your iron and thyroid checked together, not one after the other.
Shrivastava SB. Indian J Dermatol Venereol Leprol. 2009;75(1):20-7. DOI: 10.4103/0378-6323.45215As early as 1993, Headington from the University of Michigan described five different ways in which the hair cycle can tip over. In some, growing hairs leave their growth phase too early. In others, resting hairs are shed earlier than usual, or the growth phase stays permanently shortened. Medications were also among the triggers he explicitly went through.
Telogen effluvium is therefore an umbrella term, not an explanation. In their 2013 review, the Delhi dermatologists Grover and Khurana write that the diagnosis is often used like a wastebasket. Many triggers are named, they note, but clear evidence is often missing.
One more point from the research matters to me. In his review, Alfredo Rebora from Genoa emphasizes how hard excessive hair loss can hit the psyche. The complaint, he writes, deserves attention, time and empathy instead of being played down.
The hairs in your brush are yesterday's hairs. They tell the story of what was going on in your body weeks or months ago. That is frustrating, because the answer lags behind.
But it is also a relief. According to the review from Delhi, telogen effluvium does not lead to baldness. And when a trigger is gone, the easing off also takes its time. A bad day in the brush then does not mean that you are on the wrong path.
One small step for today: Write down a timeline of the past six months. Infections and fever, giving birth, a diet, new medications or dose changes, heavy bleeding, stressful periods. With this list, the conversation at your doctor's office becomes more concrete.
And now you know why the cause rarely lies in the past week, and why telogen effluvium on its own is not yet an explanation.
What do thyroid hormones do directly in the hair root?
Maybe you have heard that an underactive thyroid can make your hair thinner. Usually, it stops at that one sentence. Behind it lies one of the most exciting discoveries in hair research, and it comes from Lübeck.
The hair root is a direct recipient of thyroid hormone. It is not a passive little tube, but a mini organ with its own clock, its own metabolism and its own power plant.
In 2008, a team led by Nina van Beek and Ralf Paus at the University of Lübeck kept human scalp hair follicles growing in culture in the lab. They came from skin samples of women with normal thyroid function, obtained during facial surgery.
With T4, the cells of the hair matrix divided more, and with T3 and T4, fewer of them died. In the lab, T4 prolonged the growth phase, possibly by dialing down TGF-beta2, a signal that slows growth. The follicles also expressed the genes for the deiodinases D2 and D3 and could therefore convert T4 into T3 themselves. Pigment production in the hair also increased.
What this means for you: When hormone is lacking, the growth of your hair roots can stall. One important caveat: These are lab findings in tissue, not a study in living people.
van Beek N et al. J Clin Endocrinol Metab. 2008;93(11):4381-8. DOI: 10.1210/jc.2008-0283Five years later, the same Lübeck research group went a step further. In cultured human hair follicles, Silvia Vidali and colleagues showed that all hormones of the thyroid axis stimulated the power plants of the cells, namely TRH, TSH, T4 and T3. The mitochondria became more numerous and more active. In hair follicle cells, T3, T4 and TRH increased the production of ATP, the cell's energy currency. At the same time, T3 and T4 reduced the formation of aggressive oxygen compounds.
This is the metabolic lens of KPNI (Clinical Psychoneuroimmunology). Building a hair is heavy labor, because the hair matrix divides without pause during the growth phase. When power runs short, this construction site can be one of the first to stall. This could explain why a lack of hormone can become visible in your hair in particular.
In 2024, Salman Bin Dayel and colleagues at Prince Sattam Bin Abdulaziz University in Saudi Arabia analyzed the records of 500 women with telogen effluvium. Only women who had thyroid tests within three months of their diagnosis were included.
Of these, 248 had normal thyroid function, 150 had hypothyroidism and 102 had hyperthyroidism. Severity, measured with the SALT score, was highest in hypothyroidism, and severe cases were more common there. The mean score did not differ between normal function and hyperthyroidism.
What this means for you: Both too little and too much hormone occur in hair loss, and here, hypothyroidism was linked to the heavier loss. The numbers come from a single clinic. They say nothing about how common thyroid disorders are among all women with hair loss.
Bin Dayel S et al. Medicine (Baltimore). 2024;103(1):e36803. DOI: 10.1097/MD.0000000000036803That too much hormone can also cost you hair is stated in the very first sentence of the 2008 Lübeck paper: Both a deficiency and an excess of thyroid hormone can change hair and skin, up to and including increased shedding. In hyperthyroidism, for example in Graves' disease, hair loss is therefore also among the possible signs. More on this in Graves' disease and hyperthyroidism.
Your thyroid does not talk to your body only through a blood value. Its hormones arrive directly at the hair root, and the root apparently does some of the math itself: It may be able to convert T4 into T3.
This leads to a hypothesis, not a proven fact. A blood value can be within the target range while the root is still undersupplied. That is exactly why it is worth looking for the other links in the chain.
What you can take from this: Ask your doctor to measure TSH, free T4 and free T3 from the same blood draw. TSH alone describes the control center, not the supply in the tissues. More on this in Why TSH alone is not enough.
Biotin is in many hair supplements. In his review, the laboratory medicine specialist Amitava Dasgupta of the University of Kansas notes that healthy people generally do not benefit from biotin. Even so, it is widely taken for hair and nails. High biotin levels can interfere with some lab tests. In thyroid tests, this can make fT3 and fT4 appear falsely high and TSH falsely low, creating the picture of an overactive thyroid.
A laboratory team from Calgary led by Jessica Gifford therefore recommends leaving out biotin for 48 hours before a blood draw. Talk this through with your doctor beforehand, so that your results reflect what is going on in your body.
And now you know why your thyroid has a say not only in the pace of your metabolism, but also in the rhythm of your hair roots.
Why can a normal ferritin level still be on the low side for your hair?
Ferritin within the normal range, says your lab report. Next to it, a check mark. Maybe you have wondered how a value can be normal when your body does not feel normal at all.
Normal describes a distribution, not your needs. In hair loss with a thyroid connection, the iron stores are one of the links I most often see running low in my consultations. That is my observation, not a study result.
Ferritin is the protein in which your body stores iron. Imagine it as a pantry. As long as the pantry is full, nobody notices anything. When supplies run low, the body distributes iron by urgency, according to a widespread and biologically plausible explanation. Blood formation and oxygen transport come first. A hair root is not essential for survival and stands further back in the line.
In 2013, a team at Cairo University led by Rasheed measured ferritin and vitamin D in 80 women aged 18 to 45 with chronic telogen effluvium or female pattern hair loss. They were compared with 40 women of the same age without hair loss.
Mean ferritin was 14.7 µg/L in telogen effluvium and 23.9 µg/L in female pattern hair loss, compared with 43.5 µg/L in the control group. The more severe the hair loss, the lower the values. The authors calculated ferritin cutoffs of 27.5 and 29.4 µg/L.
What this means for you: The classic cutoff for iron deficiency is 15 µg/L, as also used in the Duke study below. So a ferritin level can look unremarkable and still fall within the range where hair loss was more common in this study.
Rasheed H et al. Skin Pharmacol Physiol. 2013;26(2):101-7. DOI: 10.1159/000346698Back in 2003, a team at the University of Pennsylvania led by Jonathan Kantor and George Cotsarelis had described a similar picture. Women with hereditary hair loss and with alopecia areata had lower ferritin levels than women without hair loss, with means of 37.3 and 24.9 versus 59.5 ng/mL. In telogen effluvium, the difference was not statistically significant in this small study.
In 2010, Elise Olsen and her team at Duke University compared data from 381 women with female pattern hair loss or chronic telogen effluvium with 76 women without hair loss.
Using the 15 µg/L cutoff, 12.4 and 12.1 percent of the premenopausal women with hair loss had iron deficiency, compared with as many as 29.8 percent in the control group. Using the 40 µg/L cutoff, the figures were 58.8, 63.8 and 72.3 percent. In this study, iron deficiency was not more common in hair loss, and whether refilling the stores changes hair was explicitly left open.
What this means for you: Low ferritin is very common in women, with and without hair loss. It is an important link in the chain, but not automatically the whole explanation.
Olsen EA et al. J Am Acad Dermatol. 2010;63(6):991-9. DOI: 10.1016/j.jaad.2009.12.006In 2006, a review from the Cleveland Clinic by Leonid Trost and Wilma Bergfeld reached a cautious conclusion. The evidence was not sufficient, they wrote, for general iron screening in hair loss or for iron without anemia. Even so, in their own clinic the authors check iron status in everyone with hair loss. By their own account, this is not strictly evidence based. But they are convinced that hair loss treatment can benefit when iron deficiency, with or without anemia, is treated as well. At the same time, they warn against too much iron, especially in hereditary hemochromatosis.
My position on ferritin
In hair loss with a thyroid connection, I aim for a ferritin level well above the lab's lower limit, often above 100 µg/L. Values between 30 and 80 µg/L are unremarkable in the lab. For hair and thyroid, I often consider them on the low side. This is a clinical position, not a guideline recommendation, and this target has not been proven for hair alone.
One reason comes from thyroid research. In a 2019 review, the nutrition scientist Margaret Rayman of the University of Surrey reports the following. In two thirds of women who still had symptoms of hypothyroidism despite appropriate levothyroxine therapy, these symptoms improved after their ferritin was raised above 100 µg/L. This is a statement from a review, not a controlled study of its own. It concerned symptoms in general, not hair specifically.
Context matters for any ferritin value. Ferritin can rise with infections, inflammation and some diseases, even when the stores are low. That is why transferrin saturation and an inflammation marker such as CRP belong on the report as well. Why inflammation can additionally block iron is explained in Iron and inflammation. You can find the debate about the target value in Ferritin above 100 as a target and in Iron deficiency despite normal ferritin.
Normal is not the same as enough. A reference range describes where the values of many people lie. It does not describe how much iron your hair root needs while your thyroid is also calling for iron to make its hormones.
With your next lab report, don't just ask: Is my ferritin normal? Ask: Where exactly is it, and how has it changed over the years? A trend often says more than a single value.
And now you know why a check mark next to your ferritin does not yet mean that this link in the chain is holding.
How can thyroid and iron slow each other down?
Maybe you have been taking iron for months, and your level barely rises. Or your thyroid is well controlled, and you are exhausted anyway. The two can be connected, and in both directions.
Thyroid and iron can slow each other down like two interlocking gears. From a KPNI perspective, this is a prime example of how the hormonal system, the immune system and metabolism can mesh together.
How thyroid, iron and hair root may be connected
- Hormonal systemAn underactive thyroid can change the cycle. In some women, periods become more irregular, sometimes also heavier. Each heavy period means a loss of iron.
- Immune systemThe stomach absorbs less. Hashimoto's often occurs together with autoimmune gastritis. The stomach then produces less acid, and iron is absorbed less well.
- MetabolismThe stores run down. Ferritin drops. The hair root, which divides without pause in the growth phase, may feel this early on.
- Hormone productionThe key enzyme loses its core. Thyroid peroxidase needs heme, and therefore iron. In one study, thyroid hormone levels were lower in marked iron deficiency.
- Feedback loopThe circle closes. When hypothyroidism was present at the same time, iron alone produced a weaker response in studies. Less hormone and less iron can thus reinforce each other.
Not every link applies to every person. The chain is a thinking model that I put together from several individual findings. As a whole, it has not been tested in any study.
The first link sounds trivial and is still often overlooked. In 1999, a team led by Krassas in Thessaloniki analyzed the menstrual periods of 171 premenopausal women with hypothyroidism. Of them, 23.4 percent had irregular periods, compared with 8.4 percent in the control group. Periods that were too infrequent and too heavy were the most common. To be fair, the authors add that such disturbances occurred less often than older textbooks described. How heavy periods affect your iron stores is covered in Iron deficiency in women.
In 2017, Miriam Cellini and the team led by Marco Centanni at Sapienza University summarized what is known about the thyrogastric syndrome. The term describes the combination of autoimmune thyroiditis and chronic autoimmune gastritis.
According to the review, Hashimoto's is linked to stomach changes in 10 to 40 percent of those affected. Conversely, about 40 percent of people with autoimmune gastritis also have Hashimoto's thyroiditis. Because the acid-producing cells of the stomach dwindle, iron deficiency anemia can develop, and later also pernicious anemia due to vitamin B12 deficiency. Levothyroxine may then also be absorbed less well.
What this means for you: If you have Hashimoto's and your iron does not rise despite tablets, your stomach is worth asking about. That belongs in a gastroenterological evaluation.
Cellini M et al. Front Endocrinol (Lausanne). 2017;8:92. DOI: 10.3389/fendo.2017.00092The fourth link sits in the thyroid itself. Josef Köhrle of the Institute of Experimental Endocrinology at Charité describes thyroid peroxidase as a heme protein, meaning an enzyme with an iron-containing core. It builds iodine into thyroglobulin, the precursor of the hormones. When iron is missing, the enzyme lacks its centerpiece.
In 1990, a team led by Beard at Pennsylvania State University studied ten women with iron deficiency anemia, eight women with depleted iron stores but no anemia, and twelve healthy women. All of them spent some time lying in cool water so that their temperature regulation could be tested.
The women with anemia had lower T4 and T3 levels and cooled down more. After iron was given, their temperature regulation improved, and their thyroid hormones partly moved closer to the values of the healthy women. The women with depleted stores but no anemia, on the other hand, responded much like the healthy women.
What this means for you: Marked iron deficiency can measurably dampen thyroid function. Whether depleted stores without anemia already do the same was left open by this small study.
Beard JL et al. Am J Clin Nutr. 1990;52(5):813-9. DOI: 10.1093/ajcn/52.5.813Hakan Cinemre and colleagues at Düzce University randomized 51 people with iron deficiency anemia and coexisting subclinical hypothyroidism in a double-blind design. One group received iron only, the other iron plus levothyroxine.
With iron alone, hemoglobin rose by an average of 0.4 g/dL, and with added levothyroxine by 1.9 g/dL. Serum iron and ferritin also rose considerably more in the combination group. A second randomized trial led by Mohammadreza Ravanbod in Bushehr, with 60 people, came to a similar result in 2013: The combination outperformed both single treatments.
What this means for you: If both iron and thyroid are struggling, one may make little progress without the other. Whether subclinical hypothyroidism is treated is a medical decision that depends on the overall picture. More on this in Subclinical hypothyroidism: treat or wait.
Cinemre H et al. J Clin Endocrinol Metab. 2009;94(1):151-6. DOI: 10.1210/jc.2008-1440 · Ravanbod M et al. Am J Med. 2013;126(5):420-4. DOI: 10.1016/j.amjmed.2012.12.009A practical point that often gets lost. In 1992, a team at the University of Calgary led by Campbell had 14 well-controlled people with hypothyroidism take a ferrous sulfate tablet at the same time as their levothyroxine for twelve weeks. TSH rose on average from 1.6 to 5.4 mU/L, and nine of the 14 developed more signs of hypothyroidism again. In the test tube, iron and thyroxine formed a poorly soluble complex.
What this means for you: If you take iron, take it at a different time from your levothyroxine. Agree on the right interval with your doctor. How coffee, breakfast and time of day matter is covered in Taking levothyroxine the right way.
The question is not: Thyroid or iron? It is: How do the two influence each other in you? If you only oil one gear, you may wonder why the gearbox keeps jamming.
If your iron does not rise despite supplements, bring three questions to your appointment. Where is the loss coming from? Is the iron being absorbed at all? And is your thyroid adjusted so that the iron has a chance? Possible causes in the gut are described in Iron deficiency from absorption problems.
If iron taken by mouth is poorly absorbed through the stomach, for example in autoimmune gastritis, an iron infusion can be a sensible option. Done well means: indication checked, iron overload ruled out, a modern preparation and monitoring during the infusion. What matters here is covered in A well-done iron infusion.
And now you know why iron and thyroid can slow each other down, and why it is worth looking at both together.
What does the conversion of T4 to T3 have to do with your hair?
Your TSH is good, and your free T4 may even be high. And still, everything feels slowed down, including your hair growth.
T4 is the key blank, T3 the finished key. The fine cutting is done by enzymes called deiodinases. These key cutters sit in many tissues, and according to the Lübeck findings, probably in the hair root as well.
The deiodinases carry selenium in their active center. Köhrle describes a dual role for the selenium-containing proteins: They protect the cells, and through the deiodinases they control when hormone is activated or switched off.
When conversion stalls, there can be plenty of T4 in the blood while little T3 reaches the tissues. Possible brakes include an energy deficit and strict diets, chronic stress, inflammation and missing building blocks. I have described this in detail in When T4 does not become T3: conversion problems and in From T4 to T3: the conversion.
What this means for hair has not been directly studied in humans. It is mechanistically plausible, though. If the hair root makes part of its T3 from T4 itself, it depends on the same building blocks and brakes as other tissues. This step has not been shown for hair so far, and I don't want to make it bigger than it is.
Zinc: a building block in both directions
In 2013, a team led by Min Seong Kil in Seoul measured blood zinc and copper in 312 people with various forms of hair loss and 30 healthy people. Mean zinc was 84.3 µg/dL in hair loss and 97.9 µg/dL in the healthy group. Copper did not differ. Values below 70 µg/dL were especially common in alopecia areata and telogen effluvium.
A team led by Ambooken Betsy at Government Medical College in Calicut, in the Indian state of Kerala, describes a case of hypothyroidism with severe hair loss. The hair loss did not improve with levothyroxine alone, only once zinc was added.
The authors explain this as an interaction. Zinc is needed to make thyroid hormone. Conversely, the body needs thyroid hormone to absorb zinc, so hypothyroidism can lead to zinc deficiency.
What this means for you: A single case is not proof. But it shows why a link that nobody measures can keep the chain open.
Betsy A et al. Int J Trichology. 2013;5(1):40-2. DOI: 10.4103/0974-7753.114714Why the ratio to copper also matters with zinc is explained in Selenium, zinc, iron and vitamin D.
Selenium: when more is not better
With selenium, the situation is particularly instructive. Here, hair loss sits on the other side of the scale.
In 2023, the nutrition panel of the European Food Safety Authority (EFSA) reassessed the tolerable upper intake level for selenium and reviewed the literature systematically for this purpose.
The panel chose hair loss as the critical endpoint, an early and well-documented sign of selenium overdose. From the large SELECT trial, it derived a lowest observed adverse effect level of 330 micrograms per day. It set the tolerable upper intake level for adults at 255 micrograms per day. According to EFSA, this level is exceeded mainly with regular use of high-dose supplements or regular consumption of Brazil nuts.
What this means for you: If you reach for more and more selenium to counter hair loss, you can end up achieving exactly the opposite.
EFSA NDA Panel, Turck D et al. EFSA J. 2023;21(1):e07704. DOI: 10.2903/j.efsa.2023.7704How pronounced this can get is shown by an outbreak in the US that was investigated by the health authority CDC. Jennifer MacFarquhar and colleagues traced it to a liquid dietary supplement that contained 200 times the stated amount of selenium. In total, 201 people in ten states fell ill. Of them, 72 percent reported hair loss, and in 29 percent it lasted 90 days or longer.
This is an extreme case, far beyond usual amounts. But it shows how sensitively the hair root can react to too much. When selenium can make sense in Hashimoto's is covered in Selenium and the thyroid.
Building blocks are not like a staircase where more always takes you higher. Too little can slow things down, too much can do harm. With selenium, of all things, hair loss is the sign the European authority uses to define too much.
If you take selenium or zinc, write down the exact amounts from all your supplements, including combination products and hair capsules. This list belongs in the discussion of your lab results.
And now you know why conversion can be an invisible link in the chain, and why the amount matters when you top up.
Is alopecia areata a thyroid issue?
There is a moment that feels completely different from diffuse thinning. During a haircut, someone shows you a round, smooth spot on the back of your head. The size of a coin.
Round bald patches are usually a matter for the immune system. Behind them, there is often alopecia areata, patchy hair loss. It is a complex autoimmune disease that leads to hair loss without scarring. And in some people, the immune system takes aim at more than one target, for example the thyroid as well.
In 2023, a team led by Sophia Ly and Arash Mostaghimi at Brigham and Women's Hospital in Boston compiled the comorbidities of alopecia areata from 102 studies. These included 680,823 people with alopecia areata and more than 72 million controls.
Hashimoto's thyroiditis was considerably more common in alopecia areata, with an odds ratio of 4.31. Among the comorbidities with data from several studies, vitamin D deficiency showed the strongest association, with an odds ratio of 10.13.
What this means for you: Alopecia areata and Hashimoto's frequently occur together. An analysis like this says nothing about cause and effect. But it shows what is worth paying attention to.
Ly S et al. Am J Clin Dermatol. 2023;24(6):875-893. DOI: 10.1007/s40257-023-00805-4A meta-analysis of 50 studies led by Solam Lee of Yonsei University came to a similar result in 2019. People with alopecia areata more often had abnormal thyroid values, positive thyroid antibodies and autoimmune thyroid diseases than the general population.
A team from Toronto led by Misaki Kinoshita-Ise took a closer look. In their meta-analysis of 17 studies, the association mainly concerned antibodies against TPO and thyroglobulin, but not diagnosed hyperthyroidism or hypothyroidism. The authors therefore see no reason for routine thyroid screening in people without symptoms. In severe and persistent cases, however, they advise staying alert to a later thyroid risk.
Telogen effluvium
Increased shedding all over the scalp, often in waves and two to three months after a trigger. The scalp looks healthy. Possible links: thyroid, iron, fever, giving birth, surgery.
Female pattern
Hair gradually becomes thinner, especially in the middle of the scalp, and the part looks wider. A hereditary predisposition often plays a role.
Alopecia areata
Round, smooth, bald patches, sometimes appearing suddenly. The immune system is involved. This belongs in a dermatologist's hands.
Mixed forms occur. According to Rebora, telogen effluvium often occurs together with hereditary hair loss.
And vitamin D? In the Cairo study, measured vitamin D in women with telogen effluvium averaged 28.8 nmol/L, compared with 118.2 nmol/L in the control group. In alopecia areata, vitamin D deficiency was the most strongly associated comorbidity in the Boston meta-analysis. Whether a low level is a cause or a consequence remains open. Still, a measurement is easy to get and belongs in the overall picture.
Round bald patches are not a hair care issue, and they are not a sign that you did something wrong. They are a signal from the immune system. That deserves a dermatological evaluation and a look at the whole immune system, including the thyroid. How autoimmunity develops in Hashimoto's is covered in Hashimoto's: causes in the immune system.
If you discover round bald patches, see a dermatologist soon and mention your Hashimoto's diagnosis there. If you have alopecia areata along with symptoms such as fatigue, feeling cold or a racing heart, TSH and thyroid antibodies are a sensible addition.
And now you know why alopecia areata and Hashimoto's can be two expressions of the same tendency of the immune system.
Can levothyroxine itself trigger hair loss?
The diagnosis is made, and you have been taking your tablet for a few weeks. And now, of all times, there is more hair in the sink than before.
According to the prescribing information, levothyroxine only rarely costs hair, and then usually temporarily. Dose and how you take it still belong in the chain.
There is sober information on this from the drug approval documents. The US prescribing information for a levothyroxine product lists hair loss among the adverse reactions. In the patient counseling section, it also says that partial hair loss may rarely occur during the first months of treatment and is usually temporary.
Why this might happen has not been conclusively studied. The hair cycle offers a plausible explanation. When hair roots restart their growth phase after a long lull, new hairs can push out the old, resting ones. Headington described patterns in which resting hairs are shed earlier than usual. For levothyroxine, however, this pathway has not been directly shown.
A second pathway is better understood: too much hormone. If the dose is higher than needed, this creates hyperthyroidism from the outside. And as described above, hyperthyroidism can itself promote hair loss.
Levothyroxine should not be stopped, reduced or increased on your own because of hair loss. Untreated hypothyroidism is itself a known trigger of diffuse hair loss. If you notice increased shedding in the first months, talk to your doctor about it. Then it can be checked whether the dose is right and whether other links in the chain are missing.
Hair loss in the first months of treatment can be part of a rebuilding process and does not have to be a setback. Whether that is the case for you is not decided by hope, but by a conversation with your doctor and a look at your values.
Write down when you started levothyroxine and when the dose was last changed. Put this date next to the start of your hair loss. If there are a few weeks to months in between, that is an important clue for the conversation. If symptoms persist despite good values, you can find more possible reasons in Symptoms despite levothyroxine.
And now you know why the tablet itself only rarely costs hair, and why its dose and the way you take it still belong in the chain.
What role does stress play for your hair and thyroid?
An exam, a breakup, caring for a relative, a year spent running nonstop. Many people tell me that their hair loss began during a time that was already too much.
Stress can tug at the hair root through the nervous system and the immune system. This is where the fourth lens of KPNI comes in: the nervous system.
Eva Peters and her psychoneuroimmunology team at Charité Berlin and the University of Giessen followed female medical students through their final exams. Eighteen women were facing the exam, and 15 served as a comparison group. Measurements were taken at three time points, twelve weeks apart.
In the exam group, perceived stress rose, and the balance of the immune system's messenger substances shifted toward a TH1 response. At the same time, hair parameters in the trichogram changed. The changes stayed within the physiological range, and at the time of the exam, the groups did not differ significantly.
What this means for you: Severe stress can temporarily slow hair growth through the immune system. It does not have to be dramatic. But it can be an additional link in a chain that is already under tension.
Peters EMJ et al. PLoS One. 2017;12(4):e0175904. DOI: 10.1371/journal.pone.0175904A group led by Ya-Chieh Hsu at Harvard University studied in mice how stress affects the stem cells of hair follicles.
Under chronic stress, the stress hormone corticosterone, the counterpart of human cortisol, kept the stem cells at rest for longer. The follicles stayed in a prolonged resting phase. The pathway ran through a signal called GAS6 in the dermal papilla, the control center at the base of the hair.
What this means for you: This reveals a possible mechanism. Whether it happens the same way in humans has not been shown.
Choi S et al. Nature. 2021;592(7854):428-432. DOI: 10.1038/s41586-021-03417-2Stress also affects the thyroid itself. High cortisol levels can shift the conversion of T4 into T3, as described in When T4 does not become T3. So the hair root and the thyroid listen to the same stress signal.
Stress is not an accusation. Nobody has earned their hair loss through the wrong kind of thinking. Stress is a biological signal that reaches the hair root, the immune system and the thyroid at the same time.
Taking it seriously does not mean treating the mind instead of the body. It means seeing both together.
A realistic start is one fixed island of recovery per day that is not up for negotiation. Ten minutes without a screen, a walk, a calm breathing rhythm. Small enough that you can stick to it every day.
And now you know why the same phase that exhausts you can also tug at your hair and your thyroid.
What concrete steps can you take now?
Maybe all of this feels like a lot. Hormone, iron, conversion, immune system, stress. The good news: You don't have to tackle everything at once.
This is not about vanity. It is about looking in the mirror in the morning and recognizing yourself. Strong hair is not a luxury. It can be a sign that the chain behind it is holding again.
Here are three steps you can start on right away.
A timeline instead of guesswork
Write down when your hair loss began and what happened in the three to four months before: fever, giving birth, surgery, a diet, new medications, dose changes, heavy bleeding, stressful periods. Also note whether the hair is falling out all over, at the part or in round patches. Photos of your part in the same light make changes comparable.
Read your labs as a chain
Ask for TSH, free T4, free T3 and thyroid antibodies from the same blood draw. Add ferritin, transferrin saturation, CRP and a blood count. Depending on your situation, vitamin D, zinc and vitamin B12 can be useful. If you take biotin, mention it before the blood draw.
Separate iron and hormone in time
Don't take iron together with levothyroxine. Agree on the interval with your doctor. If your stores don't rise despite supplements, ask why: bleeding, stomach, gut, or a thyroid that is not yet properly adjusted.
When you should see a doctor soon
- Round, bald patches or hair loss on your eyebrows, eyelashes or body. This should be evaluated by a dermatologist.
- A red, scaly, painful or scarring scalp. Causes other than telogen effluvium are possible here.
- Hair loss with a racing heart, tremor, inner restlessness and weight loss. This can point to hyperthyroidism, including a levothyroxine dose that is too high.
- Hair loss with marked fatigue, sensitivity to cold and weight gain. This can point to hypothyroidism.
- Very heavy or new bleeding, including blood in the stool. The cause of the iron loss needs to be found, not just the stores refilled.
- Hair loss after starting a new medication or after a dose change. Please don't stop anything on your own. Talk to your doctor instead.
Giving birth is a known trigger of telogen effluvium. The thyroid can also change during this time. During pregnancy and breastfeeding, separate rules apply to thyroid and iron. This calls for close medical care.
Well established
Both an underactive and an overactive thyroid can promote diffuse hair loss. Ferritin and thyroid values belong in the evaluation. Hashimoto's occurs more often in alopecia areata. Iron can interfere with the absorption of levothyroxine. Very high amounts of selenium can trigger hair loss.
Mechanistically plausible
Thyroid hormones directly influence the hair root, as shown in organ cultures. The hair root can probably convert T4 into T3 itself. Iron deficiency may dampen hormone production via thyroid peroxidase. In the animal model, stress prolonged the resting phase.
Open
Which ferritin level is optimal for hair. Whether refilling iron stores without anemia changes hair loss. Whether impaired conversion costs hair in humans. Whether low vitamin D is a cause or a consequence.
Clinical observation
In my consultations, I see again and again that in hair loss with a treated thyroid, the iron stores are often the gap. This is experience, not a study result.
Shampoo cares for the hair that has already grown. The root needs something else: hormone, iron, building blocks and rest. That is not an argument against hair care. It is an argument for knowing the order of things.
And now you know why it is worth reading your hair not as a hair care problem, but as a message from your roots.
Frequently asked questions about hair loss and the thyroid
Can an underactive thyroid cause hair loss?
Yes, an underactive thyroid is considered a known cause of diffuse hair loss. In lab experiments on human hair follicles, T4 prolonged the growth phase, and T3 and T4 reduced cell death in the hair matrix. So when hormone is lacking, the hair root may switch to the resting phase earlier. In a clinic analysis of 500 women with telogen effluvium, 150 had hypothyroidism, and their hair loss was the most severe. The shedding often becomes visible only weeks to months after the disorder begins.
Can an overactive thyroid also lead to hair loss?
Yes. Both a deficiency and an excess of thyroid hormone can disrupt the hair cycle and promote telogen effluvium. In the same analysis of 500 women, 102 had hyperthyroidism. A levothyroxine dose that is too high can also create hyperthyroidism from the outside. A racing heart, tremor, inner restlessness and weight loss are reasons for a prompt medical check.
Why is my hair falling out even though my thyroid is well controlled?
Because hair hangs on several threads. Other possible links include low iron stores, a delayed reaction to an earlier trigger, alopecia areata as an autoimmune disease, stress or hereditary thinning. In Hashimoto's, autoimmune gastritis occurs more often, and it can impair iron absorption. And iron taken together with levothyroxine can interfere with the absorption of the hormone. A TSH within the target range is therefore a prerequisite, but not the whole answer.
How long does it take for hair to grow back?
Patience is part of it. According to one review, telogen effluvium usually subsides within three to six months once the trigger is gone or treated. It then takes additional time until regrowing hair reaches visible length. According to the same paper, chronic telogen effluvium can take three to ten years to improve on its own. If there is no improvement at all after six months, it is worth taking a second look at the other links in the chain.
Which blood tests make sense for hair loss and the thyroid?
For diffuse hair loss without an obvious cause, one review recommends ferritin as well as T3, T4 and TSH, plus a blood count and urinalysis. With Hashimoto's or a suspicion of it, thyroid antibodies are added. Because ferritin can rise with inflammation, transferrin saturation and CRP are useful for interpretation. Depending on the situation, vitamin D, zinc and vitamin B12 can be useful. If you take biotin, mention it before your blood draw, because it can distort some thyroid tests.
Which ferritin level matters for hair loss?
There is no clearly proven target value for hair, and the studies contradict each other. In a study from Cairo, the ferritin cutoffs for hair loss were 27.5 and 29.4 µg/L, which is above the classic deficiency threshold of 15 µg/L. A study from Duke University, by contrast, found iron deficiency no more often in women with hair loss than in women without it. In my practice, for hair loss with a thyroid connection, I aim for a considerably higher ferritin, often above 100 µg/L. This is a clinical position, not a guideline recommendation.
Why doesn't my ferritin rise despite iron tablets?
There are several possible reasons. In Hashimoto's, autoimmune gastritis occurs more often, a condition in which the stomach produces less acid and absorbs iron less well. Ongoing losses, for example from heavy periods, can exceed intake. With coexisting subclinical hypothyroidism, hemoglobin and ferritin rose considerably more with iron plus levothyroxine than with iron alone in two randomized trials. Which of these applies to you is something for a medical evaluation.
Can I take iron and levothyroxine at the same time?
Better not. In a study of 14 people, TSH rose on average from 1.6 to 5.4 mU/L when they took ferrous sulfate together with their levothyroxine for twelve weeks. Nine of them developed more signs of hypothyroidism again. Iron binds thyroxine and can thereby reduce its absorption. Agree on the right time interval with your doctor.
Can levothyroxine itself trigger hair loss?
Rarely, and usually temporarily. The US prescribing information for a levothyroxine product lists hair loss among the adverse reactions and mentions rare, partial hair loss in the first months of treatment that is usually temporary. A dose that is too high can also cost hair by causing hyperthyroidism. That is why levothyroxine should not be stopped or changed on your own. If you notice hair loss after starting treatment or after a dose change, talk to your doctor.
Does selenium do anything for hair loss in Hashimoto's?
I have not found robust studies showing that selenium changes hair loss in Hashimoto's. Selenium is a building block of the enzymes that convert T4 into T3. At the same time, hair loss is precisely the sign that EFSA used in 2023 to set the tolerable upper intake level of 255 micrograms per day for adults. In an outbreak caused by a product containing 200 times the stated amount of selenium, 72 percent of those affected reported hair loss. So more selenium is not automatically better for your hair.
Are Hashimoto's and alopecia areata connected?
Yes, the two frequently occur together. In a meta-analysis of 102 studies, the odds ratio for Hashimoto's in people with alopecia areata was 4.31. Another meta-analysis mainly found thyroid antibodies more often, but not diagnosed hyperthyroidism or hypothyroidism more often. Round, bald patches belong in a dermatological evaluation, and if you have Hashimoto's, it is worth mentioning it there.
Does vitamin D play a role in hair loss?
There are clear associations, but no established cause. In a study from Cairo, measured vitamin D in women with telogen effluvium averaged 28.8 nmol/L, compared with 118.2 nmol/L in the control group. In alopecia areata, vitamin D deficiency was especially common in a large meta-analysis. Whether a low level is a cause or a consequence remains open. A measurement is easy to get and belongs in the overall picture.
What role does zinc play in hair loss and the thyroid?
Zinc and the thyroid influence each other. Zinc is needed to make thyroid hormone, and thyroid hormone is important for zinc absorption. In a Korean study, mean zinc was 84.3 µg/dL in people with hair loss and 97.9 µg/dL in healthy people. A case report describes hair loss in hypothyroidism that improved only after zinc was added. Zinc should be measured and discussed with a doctor before you take it long term.
Can stress make hair loss worse?
That is plausible and partly supported by evidence. In a Charité pilot study, exam stress in female medical students shifted the immune response and temporarily slowed hair growth, although within the physiological range. In the mouse model, the stress hormone corticosterone kept hair follicles in the resting phase for longer. Stress can also influence the conversion of T4 into T3. This makes it a possible additional link in the chain.
Where the topic continues
Iron deficiency and hair loss
Which ferritin level counts for your hair and how long regrowth takes.
Ferritin above 100 as a target
The debate about the target value, calmly put into context.
Iron deficiency from absorption problems
When celiac disease, H. pylori and others hold back your iron.
Iron infusion or iron tablets
When which route can make sense.
Thyroid and female hormones
How your cycle, hormones and thyroid interact.
Hashimoto's: causes in the immune system
Why the immune system attacks the thyroid.
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