Red Light Therapy Effects: What Red and Infrared Light Can Do in Your Cells

In 2018, Michael R. Hamblin of the Wellman Center for Photomedicine at Massachusetts General Hospital in Boston summarised the state of mechanism research. He describes cytochrome c oxidase as the most important light receptor and the release of nitric oxide as a hypothesis. Particularly interesting: in healthy and in stressed cells, PBM can have seemingly opposite effects. For you, this means: light never meets a neutral cell, but a cell in a particular state.

In 2020, Brendan J. Quirk and Harry T. Whelan of the Medical College of Wisconsin examined the evidence for exactly this mechanism. Their sober conclusion: reliable proof of a light-triggered effect at cytochrome c oxidase has not yet been provided. They suspect that the release of nitric oxide itself could be the core of photobiomodulation. For you, this means: the mitochondria model is plausible, but not as well established as it sounds on packaging.

In 2017, Hamblin compiled evidence that dampening inflammation is among the most reproducible effects of photobiomodulation, above all in cell and animal models. He also describes how PBM can upregulate antioxidant protective systems. At the same time, he stresses the pronounced dependence on the dose. For you, this means: the most plausible benefit lies where tissue is irritated or overloaded, not in a healthy, rested cell.

In 2011, Ying-Ying Huang and colleagues from Hamblin's research group summarised that the biphasic dose response has been shown both in cell experiments and in animal experiments. They suspect that many negative studies are due to poorly chosen dose parameters. Reactive oxygen species could be two-faced here: a signal in small amounts, damage in large amounts. For you, this means: a study without an effect often says more about the dose than about the light.

In 2011, Sulbha K. Sharma and colleagues irradiated nerve cells from mouse brains with near-infrared light at five different doses. At low doses, calcium, ATP and the mitochondrial membrane potential rose, and at high doses they fell again. Reactive oxygen species showed a second, larger rise at the highest dose. This is a cell experiment on animal cells, but it illustrates the principle very clearly.

In 2017, Caerwyn Ash and colleagues of the University of Wales Trinity Saint David in Swansea used a multi-layered skin model to calculate how light of different wavelengths penetrates tissue. Penetration depth increased with wavelength, and the greatest calculated depth was 5,378 micrometres. A light spot of ten millimetres reached 73 to 88 percent of the energy density of an infinitely wide beam at a depth of one to three millimetres. For you, this means: light gets deeper than just the outer layer of skin, but not into every organ.

In 2017, Yuguang Wang and colleagues compared two near-infrared wavelengths on human stem cells from fat tissue. 810 nanometres appeared to work mainly via cytochrome c oxidase. 980 nanometres, by contrast, worked via heat-sensitive calcium channels, presumably because water absorbed the light, and the optimal dose was 10 to 100 times lower. For you, this means: near-infrared is not simply near-infrared, and the boundary with heat is fluid.

In 2017, Adriane Aver Vanin and Ernesto Cesar Pinto Leal-Junior of the Universidade Nove de Julho in São Paulo and their team analysed 39 studies with 861 participants. In the meta-analysis, time to exhaustion, number of repetitions and strength values showed a certain advantage for light therapy. However, the quality of the evidence ranged only from very low to moderate, and the protocols differed greatly. For you, this means: there is a signal, but it stands on shaky legs.

In 2024, Bo-Ming Li and colleagues of Nanjing Normal University analysed 34 randomised trials on light before training. Endurance improved with a standardised effect size of 0.31, strength recovery with 0.24, and the muscle damage marker CK fell by an average of 77.56 units. The benefit appeared in untrained people and in athletes, but not in physically active recreational exercisers. For you, this means: whether red light does anything for you can depend strongly on where you currently stand.

In 2023, Lívia Oliveira Bezerra and colleagues summarised 16 studies with 340 healthy people. Recovery from fatigue improved with light therapy. They found no increase in strength or functional performance. For you, this means: red light is no substitute for the training that makes you stronger.

In 2025, Murilo S. Canez and colleagues of the Federal University of Pelotas compared light, pneumatic compression and electrical muscle stimulation. Light before exertion reduced muscle soreness by 12.27 points on the respective scale. However, they rated the certainty of this evidence as low. For you, this means: among the devices tested, light performed best, without the data being particularly strong.

In 2026, Hongxiu Chen and colleagues of Khon Kaen University in Thailand examined whether light increases the strength gains of older people in resistance training. Compared with a sham treatment, the difference, with an effect size of 0.26, was not statistically significant. A small effect could not be ruled out, however. For you, this means: the dumbbell remains the main stimulus, and light is at most a footnote.

In 2019, Yehuda Zadik and the mucositis study group of the professional societies MASCC and ISOO evaluated the body of evidence for a guideline. They recommend PBM for preventing oral mucositis in stem cell transplantation and in radiotherapy of the head and neck region, with or without chemotherapy. For the treatment of mucositis that is already present, however, the evidence was insufficient. Important: the recommendation only applies if all parameters of a tested protocol are followed exactly.

In 2024, Bin Shen and colleagues of Shaoxing People's Hospital summarised 14 randomised trials with 869 people with head and neck cancer. Severe mucositis occurred less often up to the end of treatment, with a relative risk of 0.45. Pain from the inflammation of the lining of the mouth was also lower. For you, this means: under strictly controlled conditions, light can noticeably support a very burdened tissue.

In 2019, Martin Bjørn Stausholm and colleagues of the University of Bergen evaluated 22 placebo-controlled studies. At the end of therapy, pain was 14.23 millimetres lower on a 100-millimetre scale than with placebo, and 18.71 millimetres lower at the recommended doses. No side effects were reported. The authors themselves stress that laser therapy has not so far been recommended in major osteoarthritis guidelines.

In 2024, Sofia Oliveira and colleagues of the University of Minho arrived at a similar effect on pain at rest with ten studies. However, all studies had an unclear to high risk of bias, and the certainty of the evidence was very low. The authors therefore advise using PBM not on its own, but at most as a complement to other recommended therapies. For you, this means: movement and strengthening remain the basis, and light could complement them.

Alexander Wunsch and Karsten Matuschka from Heidelberg treated 113 people twice a week with red light or a broad red-infrared spectrum and compared them with 23 control subjects. After 30 sessions, skin appearance, skin roughness and collagen density measured by ultrasound improved, and blinded evaluation of photos confirmed this. The broad spectrum brought no advantage over pure red light. For you, this means: an encouraging result, but a single study, not a guarantee of skin that looks ten years younger.

In 2021, Christin Henein and David Steel reviewed the studies available at the time for the Cochrane Collaboration. They found only two small randomised trials. For vision after twelve months, there was no meaningful difference compared with sham or no treatment, with low certainty of evidence. For you, this means: at that point it remained open whether PBM can slow progression.

In 2026, Glenn J. Jaffe and colleagues reported the 24-month data from the LIGHTSITE III trial. After 21 months, visual acuity in the light group was on average 6.2 letters higher, and an advanced form, geographic atrophy, occurred less often: in 6.8 versus 24.0 percent. Several of the authors, however, work for the manufacturer of the device used. For you, this means: an interesting signal that needs independent confirmation and belongs exclusively in the hands of an ophthalmologist.

In 2026, Lisa A. Ostrin and Alexander W. Schill of the University of Houston College of Optometry measured the light output of four red light devices for treating short-sightedness in children. With a dilated pupil, two laser devices reached the Group 1 safety limit after just 2.8 and 1.4 seconds, with a recommended treatment time of 180 seconds. An LED device with diffuse light stayed far below this. For you, this means: the problem is not red light as such, but power, focusing and looking directly into the source.

In 2018, Hamblin and two co-authors with company affiliations described how some animal studies suggest an unfavourable influence on tumours, while others suggest a favourable one. Their conclusion: PBM could be of benefit in cancer patients and should be investigated further. That is deliberately cautious wording. For you, this means: light does not belong on the skin over known or unclear tumours and conspicuous skin areas without consulting an oncologist.