Red light therapy is the practice of exposing skin and the tissue beneath it to low-power red light (roughly 600 to 700 nanometres) and near-infrared light (roughly 780 to 1,100 nanometres) from LEDs or low-level lasers, at intensities meant not to heat or burn. Researchers call it photobiomodulation, or PBM; older names are low-level laser therapy (LLLT) and "laser biostimulation". The working idea is that particular wavelengths are absorbed by molecules inside cells and shift how those cells function, rather than acting through warmth.
It matters because the technology has moved from research labs into bathrooms and gyms. Panels, face masks, wands, caps and belts are now sold for home use, often with claims that run well ahead of the studies. This guide sets out where the field came from, the proposed mechanism, what the human evidence cautiously supports, what it does not, and how to use a device safely. It belongs to the evidence-first series collected on the biohacking topic hub.
What is red light therapy?
Red light therapy is the application of specific red and near-infrared wavelengths to the body at low power, usually for a few minutes per area. Most consumer panels and masks use red light at about 630 to 670 nm and near-infrared at about 810 to 850 nm, often combined in one device. Red light is visible; near-infrared is not.
Low power is part of the definition. The aim is a photochemical effect, in which light is absorbed and triggers a change in cell chemistry, not a thermal one. That separates red light therapy from three things it is often confused with. Infrared saunas work mainly by raising body temperature, so their effects come from heat. UV tanning beds expose skin to ultraviolet radiation, which red and near-infrared devices do not emit. Blue-light devices use shorter wavelengths, around 400 to 470 nm, which are absorbed by different molecules and are studied for different purposes.
Where did photobiomodulation come from?
The field traces back to the Hungarian surgeon Endre Mester (1903 to 1984), professor at Semmelweis Medical University in Budapest, who began publishing on low-intensity lasers in 1967, only seven years after the first working laser was built. Mester wanted to know whether laser light might cause cancer. He shaved the backs of mice and exposed one group to a low-power ruby laser, which emits at 694 nm. The irradiated mice did not develop cancer, and, to his surprise, the hair on their shaved patches grew back faster than on the unexposed controls. He called the observation "laser biostimulation".
From 1971 Mester began applying low-intensity lasers to patients with chronic, slow-healing skin wounds, and in 1974 he founded the Laser Research Center at the university, where he worked for the rest of his life.
The vocabulary changed as the hardware did. Once LEDs replaced many lasers, "low-level laser therapy" became "low-level light therapy", and the meaning of "low-level" was always vague. In 2015 Juanita Anders, Raymond Lanzafame and Praveen Arany argued in Photomedicine and Laser Surgery for "photobiomodulation therapy" as the clearer term, and it is now the standard name in the research literature.
How is red light supposed to work in the body?
The leading explanation is that red and near-infrared light is absorbed by cytochrome c oxidase, an enzyme in the mitochondria, the structures that produce most of a cell's usable energy. The hypothesis is closely associated with the biophysicist Tiina Karu, whose experiments in the 1980s and 1990s found that the wavelengths that changed cell behaviour lined up with the light-absorbing bands of this enzyme.
The downstream story runs like this. Absorbed light is thought to alter the enzyme's activity, with reported changes in the production of ATP, the cell's energy currency, in the release of nitric oxide, and in short-lived signalling molecules that switch genes on and off. Researchers have proposed other light-absorbing targets too, including water and light-sensitive ion channels in cell membranes.
The honest summary is that this mechanism is well supported in cell cultures and animal studies, and is still being worked out in people. It does not, on its own, show that any particular device produces a meaningful result in a human body.
Why does the dose matter so much?
The response to red light is dose-dependent and biphasic: too little does nothing, a moderate amount produces an effect, and too much can blunt or reverse it. A 2009 review by Ying-Ying Huang, Michael Hamblin and colleagues in the journal Dose-Response laid out this pattern, often compared to the older Arndt-Schulz rule in pharmacology.
Dose in photobiomodulation has several parts: the wavelength, the irradiance (power per square centimetre reaching the skin), the exposure time, the distance from the emitter and the resulting energy density, usually given in joules per square centimetre. Each can vary enormously between devices. A handheld wand held against the skin, a mask a few millimetres away and a full-body panel used at arm's length deliver very different doses even at the same wavelength, and intensity falls off quickly with distance.
This is why studies are hard to compare and home results hard to predict. It is also why "more is better" is the wrong instinct. Longer or closer sessions than a manufacturer specifies are not supported by the research and raise the risk of heat discomfort or burns from high-output units.
What does the evidence cautiously support?
The best-supported uses are cosmetic and performance-related, and even there the evidence is modest. Three areas stand out.
Skin appearance
The most cited trial is by Alexander Wunsch and Karl Matuschka, published in Photomedicine and Laser Surgery, volume 32, issue 2, in 2014. It included 136 volunteers who received twice-weekly sessions, 30 in total, of either 611 to 650 nm red light or a broader 570 to 850 nm spectrum, or no light at all. The light groups reported better complexion and skin feel, showed reduced roughness on measurement, and had higher collagen density on ultrasound than the controls.
Two caveats matter. The control group received no sham session, so expectation effects cannot be ruled out. And the broader spectrum did no better than red alone, which is a useful counterweight to marketing that presents more wavelengths as automatically better.
Hair
Several sham-controlled trials of home laser combs and caps have reported higher hair counts in measured areas of the scalp than sham devices over a period of months. Specific devices have received FDA 510(k) clearance for narrow labelled uses. Clearance is not approval: it means the regulator accepted that the device is substantially equivalent to one already on the market, and it covers only that device and the use written on its label, not red light in general.
Exercise performance and recovery
Small trials and meta-analyses, including a 2015 systematic review led by Ernesto Leal-Junior in Lasers in Medical Science, suggest that light applied to muscles before exercise may modestly support performance measures, such as repetitions or time to exhaustion, and some recovery markers. Results are mixed and study quality varies, so this remains a promising area rather than a settled one.
What the evidence does not support
The evidence does not support most of the broader claims made for consumer red light devices. There is no good evidence for general fat-loss or weight-loss claims, and "detox" claims have no clear biological meaning to test. Claims that home panels improve sleep or mood rest on thin evidence; for sleep in particular, the better-established habits remain a regular schedule, morning daylight and dim evenings, covered in the site's guide to the science of sleep.
Above all, nothing in the current literature supports using a home device to address any disease. Clinical photobiomodulation in specialist settings is a separate research area with its own protocols, and its results do not transfer to a consumer mask or panel. Any device described as "FDA-approved" for red light wellness deserves suspicion, since that is not how these products are regulated.
Is red light therapy safe?
Used as directed, red light therapy is generally low-risk for healthy adults, but a few precautions are non-negotiable, starting with the eyes.
Never look directly into the emitters. Near-infrared light is invisible, so the eye does not register its brightness and the blink reflex offers no protection. With high-output panels, wear the goggles supplied with the device. In July 2019 a major skincare brand voluntarily recalled its LED face mask sold for blemish-prone skin, citing a theoretical risk of eye injury for people with certain eye conditions or those taking medication that increases light sensitivity.
Check with a clinician before starting if you take photosensitising medication, have an eye or skin condition, have an unexplained or changing skin lesion, or are pregnant. High-power units can cause heat discomfort and burns, so follow the manufacturer's timing and distance guidance and stop if the skin becomes hot or irritated.
Finally, be a sceptical buyer. Many consumer "wellness" devices have no FDA clearance at all. Ask what wavelength and what irradiance a device actually delivers at the distance it is meant to be used, and whether those figures were measured independently.
Billy Carson's reading
Billy Carson has not published a dedicated talk, video or post on red light therapy or photobiomodulation, and this article does not attribute any position on the subject to him. What his wider work does show is how a practice like this fits. In the site's pillar on biohacking for beginners, his approach is framed as consciousness-first: sleep, movement, food timing and breath are maintenance for the body, and the reason to look after them is to have more energy and clarity for inner work rather than to chase a number on a device.
Read that way, red light belongs in the optional tier of biohacking, after the fundamentals and with the same evidence-first scrutiny the site applies to every tool. The same balance runs through the guides to grounding and earthing and to breathwork and the Wim Hof Method: describe the practice, report what the studies show, and set out the limits plainly.
Watch, read and go deeper
For the habits that come before any device, start with the biohacking for beginners guide, which sets sleep, light, movement, breath and fasting alongside the evidence for each. The site's earlier overview of how technology entered the biohacking movement gives the wider context for wearables and light devices. For daylight, darkness and rest, continue with the science of sleep. Every evidence-focused guide on the subject is collected on the biohacking topic hub.
Frequently asked questions
Does red light therapy actually work?
The cell and animal research shows that red and near-infrared light can change how cells behave, and some human trials report modest cosmetic and exercise-related effects. The human evidence is still limited, many studies are small or lack a sham control, and results depend heavily on dose. It is reasonable to describe red light therapy as promising for a few narrow uses and unproven for most of what is marketed.
What wavelengths are used in red light therapy?
Most research and most consumer devices use red light between about 630 and 670 nm and near-infrared light between about 810 and 850 nm. Wavelength is only one part of the dose; irradiance, time and distance matter as much.
How often do people use red light therapy?
Study protocols vary widely; the 2014 Wunsch and Matuschka skin trial, for example, used two sessions a week for a total of 30. There is no established home dose, because devices differ so much in output. Following the manufacturer's timing and distance guidance is the sensible default, and longer sessions are not better.
Is red light therapy the same as an infrared sauna?
No. An infrared sauna works by heating the body, so its effects come from raised temperature. Red light therapy uses low-power light at specific wavelengths and is designed not to heat tissue, with any effect thought to come from light absorption inside cells.
Is red light therapy safe for the eyes?
Not if you look into the emitters. Near-infrared light is invisible, so the blink reflex does not protect the eyes, and high-output panels should be used with the supplied goggles. Anyone with an eye condition or taking light-sensitising medication should consult a clinician before using any light device.
Sources and further reading
- Endre Mester and colleagues, early papers on laser biostimulation in mice and in slow-healing skin wounds (1967 to 1971).
- Tiina Karu, "Primary and secondary mechanisms of action of visible to near-IR radiation on cells," Journal of Photochemistry and Photobiology B: Biology (1999).
- Ying-Ying Huang, Aaron Chen, James Carroll and Michael Hamblin, "Biphasic dose response in low level light therapy," Dose-Response (2009).
- Juanita Anders, Raymond Lanzafame and Praveen Arany, "Low-level light/laser therapy versus photobiomodulation therapy," Photomedicine and Laser Surgery (2015).
- Michael Hamblin, "Photobiomodulation or low-level laser therapy," Journal of Biophotonics (2016).
- Alexander Wunsch and Karl Matuschka, controlled trial of red and near-infrared light on skin roughness and intradermal collagen density, Photomedicine and Laser Surgery 32(2) (2014).
- Ernesto Leal-Junior and colleagues, systematic review and meta-analysis of phototherapy and exercise performance and recovery, Lasers in Medical Science (2015).
This article is for general information. Anyone considering red light therapy, particularly with a medical condition, a skin or eye concern, photosensitising medication or a pregnancy, should consult a clinician first.
These statements have not been evaluated by the Food and Drug Administration. This content is for information only and is not medical advice.
