Red light and near-infrared light (roughly 600-900 nm) are absorbed by cytochrome oxidase in mitochondria. That step hands electrons to oxygen. Absorption can raise ATP and free the enzyme from inhibitory nitric oxide.

Practical use: red or near-IR lamps on skin and tissue for inflammation, recovery, and local energy. See Mitochondria.

Mechanism

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Cytochrome c oxidase is the thyroid-sensitive, oxygen-reacting bottleneck of respiration. Inhibitors include nitric oxide, carbon monoxide, estrogen, PUFA, serotonin, excess iron, radiation, and endotoxin. Red light reactivates the enzyme in the same literature line used for endotoxin and estrogen mitochondrial damage.[1]

After UV or other radiation injury, red light can quench ongoing free-radical production in tissue. See Radiation, Inflammation. Pre-treating human skin fibroblasts with non-coherent near-infrared radiation (700-2000 nm), without any measurable temperature rise, protected the cells against subsequent solar UV toxicity; the protection lasted at least 24 hours and did not depend on new cell division or new protein synthesis.[2]

Resting energy expenditure

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In a randomized crossover trial, women with obesity who received a short (12 min) whole-torso photobiomodulation session (red 633-660 nm plus NIR 850-940 nm) showed an acute rise in resting energy expenditure versus pre-exposure (~+9%), without a change in respiratory exchange ratio; the sham condition did not produce that pattern, and normal-weight women showed a smaller effect.[3] That supports an acute metabolic-rate effect of red/NIR light in a stressed metabolic phenotype; it is not a substitute for thyroid, diet, or PUFA reduction.

Gut microbiome

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Photobiomodulation applied to the abdomen shifted gut microbiome composition in mice, a result the same research group later reported confirming in humans, likely through effects on metabolism and circadian signaling rather than direct contact with gut bacteria.[4]

Fatty liver

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In a 12-week randomized trial in 60 obese older adults (65-75) with confirmed non-alcoholic fatty liver disease, adding twice-weekly 660 nm laser (30 min, applied over the abdomen) to a Mediterranean diet outperformed the same diet alone on every measure tracked. Waist circumference fell about 15 cm in the laser group versus about 6-7 cm on diet alone (men: 109.1 to 94.0 cm vs 109.7 to 103.0 cm; women: 99.1 to 84.6 cm vs 100.7 to 93.9 cm); BMI, liver enzymes (AST, ALT, ALP), and the full lipid panel (lower total cholesterol, LDL, triglycerides; higher HDL) all improved more in the laser group, and both groups' baseline values had been matched by randomization.[5] The diet in both arms already accounts for much of the effect, red light added an additional, statistically significant benefit on top of it rather than acting alone. See Fatty liver disease for the PUFA/endotoxin mechanism this fits into.

Cognition and Alzheimer's disease

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In a randomized, double-blind, placebo-controlled trial of 93 older adults (age 50 and up) with mild cognitive impairment, 60 days of transcranial photobiomodulation improved cognition on the Montreal Cognitive Assessment more than placebo (delta +3.20 vs +1.97, p=0.0301) and raised serum BDNF (delta +821.94 vs +359.41, p=0.0046). The cognitive gain held at a 150-day follow-up. Depression, anxiety, resilience scores, and the neurodegeneration markers NSE and S100B did not differ between groups.[6]

In cell models of Alzheimer's disease (APP/PS1 primary neurons and SH-SY5Y cells expressing human APPswe), photobiomodulation raised cytochrome oxidase activity, ATP, and cAMP, activating PKA and SIRT1. SIRT1 activation increased ADAM10 and lowered BACE1, shifting amyloid precursor protein processing away from the amyloidogenic pathway and reducing amyloid-beta production.[7]

Myopia

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In a single-center, single-masked randomized controlled trial of 224 children (ages 6-12) with myopia, 6 months of repeated low-level red light therapy (650 nm, 3 min, twice daily, at least 4 hours apart) outperformed single-vision spectacles on both structural outcomes tracked. Median axial length shortened by 0.06 mm in the treated group versus lengthening 0.14 mm in the control group; subfoveal choroidal thickness increased 15 µm in the treated group versus decreasing 7 µm in controls (both p<0.001). Axial shortening occurred in 63.74% of treated children versus 2.27% of controls.[8]

Scalp irritation and pruritus

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In a randomized, double-blind, sham-controlled trial of 81 adults with androgenetic alopecia, daily 10-minute home use of a dual-wavelength (620 nm and 660 nm) LED device for 16 weeks outperformed a matched sham device on scalp symptoms. All active-treatment subjects (100%) reported "never" or "rarely" having burning or stinging, versus 66.6% on sham (p=0.007). Itching was "never" or "rarely" present in 77.8% of the active arm versus 44% on sham, and irritation in 83.4% versus 55.5% on sham; those two differences did not reach statistical significance (p=0.2 and p=0.07). Study authors, funded by the device's maker, attribute the effect to 620 nm light raising local nitric oxide release and 660 nm light raising ATP production while lowering inflammatory cytokines.[9]

Ocular red light and reproductive hormones

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In male donkeys during the non-breeding season, 6 hours daily of red LED light directed at a single eye raised plasma testosterone, LH, FSH, AMH, and Activin A while lowering melatonin, restarting reproductive-axis activity without any change to diet or housing; red light outperformed blue and white light in the same trial.[10] This is animal data, not a human trial, but it fits the pattern of light entering through the eye acting on the hypothalamic-pituitary-gonadal axis via melatonin suppression rather than only through direct skin/tissue absorption.

Photoreceptor aging

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In adults aged 28-72, brief daily exposure to 670 nm red light improved rod-mediated dark-adapted (night) vision and blue-cone contrast sensitivity specifically in participants over 40, consistent with mitochondrial decline in photoreceptors driving age-related vision loss; the red (protan) axis improved but not significantly, and the effect was strongest with lower irradiance (8 mW/cm2) rather than higher.[11]

Caveats

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Peat cautioned against assuming isolated red light is automatically safe just because it is used therapeutically. His concern was single-wavelength ("pure") red light specifically, not full-spectrum sources such as incandescent lamps or sunlight.

There isn't enough skepticism about what pure red lights are doing, but there is data showing it can make cancer grow, where the incandescent or sunlight type of absorption and resonance, no one has ever seen those effects from a full spectrum.

— Ray Peat

[12]

Practice

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Distance and time set dose. Skin should warm without burning. Eyes need care with bright LEDs. Morning and post-injury use appear in practical bioenergetic notes. Pair with whole-body supports: thyroid, sugar oxidation, lower PUFA. See Thyroid, CO2, PUFA, Activities.

See also

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References

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  1. ↑ "Ray Peat, PhD on Endotoxin"
  2. ↑ Menezes S, Coulomb B, Lebreton C, Dubertret L. "Non-coherent near infrared radiation protects normal human dermal fibroblasts from solar ultraviolet toxicity," J Invest Dermatol. 1998;111(4):629-33. doi:10.1046/j.1523-1747.1998.00338.x. PMID 9764844.
  3. ↑ De Nardi M, et al. "Photobiomodulation Acutely Augments Resting Metabolism in Women with Obesity," Nutrients. 2025;17(21):3357. PMC12608151.
  4. ↑ Ann Liebert, Brian Bicknell, Daniel M Johnstone, Luke C Gordon, Hosen Kiat, Michael R Hamblin, "'Photobiomics': Can Light, Including Photobiomodulation, Alter the Microbiome?" Photobiomodulation, Photomedicine, and Laser Surgery 37, no. 11 (2019), https://pubmed.ncbi.nlm.nih.gov/31596658/
  5. ↑ Nagy EN, Ibrahim FM, Jouda AA, Elsayed MM. "The Effect of Laser Therapy Along With Mediterranean Diet Versus Mediterranean Diet Only on Older Adults With Non-alcoholic Fatty Liver Disease: A Randomized Clinical Trial," J Lasers Med Sci. 2021;12:e39. doi:10.34172/jlms.2021.39.
  6. ↑ de Oliveira BH, Lins EF, Kunde NF, Salgado ASI, Martins LM, Bobinski F, Vieira WF, Cassano P, Quialheiro A, Martins DF. "Transcranial photobiomodulation increases cognition and serum BDNF levels in adults over 50 years: A randomized, double-blind, placebo-controlled trial," J Photochem Photobiol B. 2024;260:113041. doi:10.1016/j.jphotobiol.2024.113041. PMID 39423445.
  7. ↑ Zhang Z, Shen Q, Wu X, Zhang D, Xing D. "Activation of PKA/SIRT1 signaling pathway by photobiomodulation therapy reduces Aβ levels in Alzheimer's disease models," Aging Cell. 2020;19(1):e13054. doi:10.1111/acel.13054. PMC6974721.
  8. ↑ Jiang Y, Zhu Z, Tan X, et al. "Effect of Repeated Low-Level Red-Light Therapy for Myopia Control in Children: A Multicenter Randomized Controlled Trial," Ophthalmology and Therapy. 2022;11(6):1971-1987. doi:10.1007/s40123-022-00585-w. PMC9587157. PMID 36208391.
  9. ↑ Nestor MS, Berman B, Sinclair R, Medendorp N, Womble M, Stasko N. "Clinical Efficacy of an At-Home, 620 and 660 nm Red Light Treatment on Scalp Pruritus and Irritation," presented Jan. 21, 2020; reported in Petronelli M. "Red-light treatment proven successful for scalp pruritus, irritation," Dermatology Times. April 28, 2020.
  10. ↑ "Effect of Monochromatic Red, Blue, and White Light on Reproductive Hormones of Male Donkeys During the Non-Breeding Season." PMID 41681471.
  11. ↑ Shinhmar H, Grewal MK, Sivaprasad S, Hogg CR, Chong V, Neveu MM, Jeffery G. "Optically Improved Mitochondrial Function Redeems Aged Human Visual Decline," J Gerontol A Biol Sci Med Sci. 2020;75(9):e49-e52. doi:10.1093/gerona/glaa155. PMID 32596723.
  12. ↑ Ray Peat, Generative Energy #78, "CO2 | Art and Science | Supply Shortages | Killer Austerity | Authoritarianism," interview with Danny Roddy, January 28, 2022, 56:11.