The science behind red-light therapy
Red light therapy at 630 nm and 660 nm, and near-infrared (NIR) light at 810 nm, 830 nm, and 850 nm, have demonstrated several benefits in the context of musculoskeletal injury recovery, skin aging and collagen production, and anti-inflammatory effects.
Musculoskeletal injury and wound healing: Both red (630–660 nm) and NIR (810–850 nm) wavelengths enhance wound healing by promoting fibroblast proliferation, collagen synthesis, and angiogenesis, while reducing inflammation. Specifically, 630 nm red light upregulates COL1A1, COL2A1, and VEGF, and reduces IL-1β, supporting tissue regeneration and anti-inflammatory effects.[1] NIR at 810 nm and 850 nm is particularly effective in accelerating wound closure, enhancing collagen accumulation, and promoting re-epithelialization, likely via mitochondrial cytochrome c oxidase activation.[2-5]
Skin aging and collagen production: Red and NIR light (notably 630, 640, 660, 830, and 850 nm) increase the expression of collagen and elastin genes and proteins in human dermal fibroblasts and skin explants, supporting anti-aging and photorejuvenation effects. 660 nm red light produces a durable increase in ATP and procollagen synthesis, while 850 nm NIR stimulates metabolic activity and procollagen I production, especially under physiologic oxygen conditions.[5-8] These effects are associated with improved skin texture and reduced photoaging.
Anti-inflammatory and systemic effects: Red and NIR light (630–850 nm) generally exert anti-inflammatory effects by modulating cytokine production and reducing oxidative stress, which may contribute to improved recovery from injury and reduced chronic inflammation.[1][9-10]
Mood and other potential benefits: While the literature provided does not directly address mood, NIR wavelengths (particularly 810 nm) have been explored for neural stimulation and neuromodulation, suggesting possible benefits in neuroregeneration and cognitive function, though robust clinical evidence is limited.[11]
In summary, red and NIR light at 630, 660, 810, 830, and 850 nm support wound healing, collagen production, and anti-inflammatory effects, with the most robust evidence for skin and musculoskeletal recovery. Effects are wavelength- and cell-type dependent, and optimal dosing parameters remain an area of ongoing research.[1-10][12]
1.
Kuppa SS, Kang JY, Kim JY, et al.
Lasers in Medical Science. 2025;40(1):171. doi:10.1007/s10103-025-04432-9.
New Research
This study examines the effects of 630 nm red-light laser therapy on wound healing, with a focus on VEGF-mediated angiogenesis and collagen production. The effectiveness of red-light therapy is influenced by critical parameters, including treatment duration and distance, which often lack standardization across protocols. To address this, we conducted cell viability and scratch wound assays using NIH/3T3 cells in-vitro to identify optimal treatment conditions. Treatment durations of 10 s, 30 s, 60 s, and 5 min, along with distances of 3 cm and 5 cm, were evaluated. Following parameter optimization, the wound-healing efficacy of red-light therapy was assessed in-vivo using nude mice. Standardized 4 mm wounds were created using a biopsy punch, and healing was evaluated at 7 and 21-days post-intervention. Histological analysis was performed, and gene and protein expression levels of COL1A1, COL2A1, VEGF, and IL-1β, which are implicated in wound healing, were assessed via RT-PCR, western blotting, and immunohistochemistry. Results demonstrated that red-light laser therapy significantly upregulated collagen and VEGF expression while reducing IL-1β levels at the three-week time point (p < 0.05). Notably, these effects were comparable to hydrogel treatment, which served as a positive control to assess the efficacy of light-emitting diode (LED)-based therapy. These findings indicate that red-light therapy effectively promotes wound healing by enhancing collagen synthesis and VEGF-mediated angiogenesis within the wound bed.
2.
Gupta A, Dai T, Hamblin MR.
Lasers in Medical Science. 2014;29(1):257-65. doi:10.1007/s10103-013-1319-0.
Low-level laser (light) therapy (LLLT) promotes wound healing, reduces pain and inflammation, and prevents tissue death. Studies have explored the effects of various radiant exposures on the effect of LLLT; however, studies of wavelength dependency in in vivo models are less common. In the present study, the healing effects of LLLT mediated by different wavelengths of light in the red and near-infrared (NIR) wavelength regions (635, 730, 810, and 980 nm) delivered at constant fluence (4 J/cm(2)) and fluence rate (10 mW/cm(2)) were evaluated in a mouse model of partial-thickness dermal abrasion. Wavelengths of 635 and 810 nm were found to be effective in promoting the healing of dermal abrasions. However, treatment using 730- and 980-nm wavelengths showed no sign of stimulated healing. Healing was maximally augmented in mice treated with an 810-nm wavelength, as evidenced by significant wound area reduction (p < 0.05), enhanced collagen accumulation, and complete re-epithelialization as compared to other wavelengths and non-illuminated controls. Significant acceleration of re-epithelialization and cellular proliferation revealed by immunofluorescence staining for cytokeratin-14 and proliferating cell nuclear antigen (p < 0.05) was evident in the 810-nm wavelength compared with other groups. Photobiomodulation mediated by red (635 nm) and NIR (810 nm) light suggests that the biological response of the wound tissue depends on the wavelength employed. The effectiveness of 810-nm wavelength agrees with previous publications and, together with the partial effectiveness of 635 nm and the ineffectiveness of 730 and 980 nm wavelengths, can be explained by the absorption spectrum of cytochrome c oxidase, the candidate mitochondrial chromophore in LLLT.
3.
Yadav A, Gupta A.
Photodermatology, Photoimmunology & Photomedicine. 2017;33(1):4-13. doi:10.1111/phpp.12282.
The innumerable intricacies associated with chronic wounds have made the development of new painless, noninvasive, biophysical therapeutic interventions as the focus of current biomedical research. Red and near-infrared light-induced photobiomodulation therapy appears to emerge as a promising drug-free approach for promoting wound healing, reduction in inflammation, pain and restoration of function owing to penetration power in conjunction with their ability to positively modulate the biochemical and molecular responses. This review will describe the physical properties of red and near-infrared light and their interaction with skin and highlight their efficacy of wound repair and regeneration. Near-infrared (800-830 nm) was found to be the most effective and widely studied wavelength range followed by red (630-680 nm) and 904 nm superpulsed light exhibiting beneficial photobiomodulatory effects on impaired dermal wound healing.
4.
Topaloglu N, Özdemir M, Çevik ZBY.
Photodermatology, Photoimmunology & Photomedicine. 2021;37(3):253-262. doi:10.1111/phpp.12645.
Background: Photobiomodulation (PBM) depends on the use of non-ionizing light energy to trigger photochemical changes, particularly in light-sensitive mitochondrial structures. It triggers proliferation and the metabolic activity of the cells, primarily by utilizing the energy from the near-infrared to the red wavelength of the light.
Purpose: This in vitro study has analyzed comparatively the most appropriate energy doses and wavelengths to induce PBM on keratinocytes and fibroblasts for the accelerated wound healing process.
Methods: 1, 3, and 5 J/cm energy densities of 655 and 808-nm diode lasers were used to promote cell proliferation and wound healing process. Scratch assay and MTT analysis were performed on keratinocytes and fibroblasts for wound closure and cell proliferation after the triple light applications, respectively.
Results: 655-nm of wavelength was more successful on keratinocytes to induce wound healing and cell proliferation, whereas 808-nm of wavelength was so effective on fibroblasts to heal the wounds totally and it induced cell proliferation almost 3 times compared to the untreated control group.
Conclusion: This study revealed that PBM with 655 and 808 nm of wavelengths was effective to speed up the wound healing process at specific energy densities. In general 808-nm of wavelength was more successful. However, the proper wavelength and the energy density may differ according to the cell type. Thus, every light parameter should be chosen properly to obtain better outcomes during PBM applications.
5.
Mignon C, Uzunbajakava NE, Castellano-Pellicena I, Botchkareva NV, Tobin DJ.
Lasers in Surgery and Medicine. 2018;50(8):859-882. doi:10.1002/lsm.22823.
Background Objectives: The past decade has witnessed a rapid expansion of photobiomodulation (PBM), demonstrating encouraging results for the treatment of cutaneous disorders. Confidence in this approach, however, is impaired not only by a lack of understanding of the light-triggered molecular cascades but also by the significant inconsistency in published experimental outcomes, design of the studies and applied optical parameters. This study aimed at characterizing the response of human dermal fibroblast subpopulations to visible and near-infrared (NIR) light in an attempt to identify the optical treatment parameters with high potential to address deficits in aging skin and non-healing chronic wounds.
Materials And Methods: Primary human reticular and papillary dermal fibroblasts (DF) were isolated from the surplus of post-surgery human facial skin. An in-house developed LED-based device was used to irradiate cell cultures using six discrete wavelengths (450, 490, 550, 590, 650, and 850 nm). Light dose-response at a standard oxygen concentration (20%) at all six wavelengths was evaluated in terms of cell metabolic activity. This was followed by an analysis of the transcriptome and procollagen I production at a protein level, where cells were cultured in conditions closer to in vivo at 2% environmental oxygen and 2% serum. Furthermore, the production of reactive oxygen species (ROS) was accessed using real-time fluorescence confocal microscopy imaging. Here, production of ROS in the presence or absence of antioxidants, as well as the cellular localization of ROS, was evaluated.
Results: In terms of metabolic activity, consecutive irradiation with short-wavelength light (⇐530 nm) exerted an inhibitory effect on DF, while longer wavelengths (>=590 nm) had essentially a neutral effect. Cell behavior following treatment with 450 nm was biphasic with two distinct states: inhibitory at low- to mid- dose levels (<=30 J/cm ), and cytotoxic at higher dose levels (>30 J/cm ). Cell response to blue light was accompanied by a dose-dependent release of ROS that was localized in the perinuclear area close to mitochondria, which was attenuated by an antioxidant. Overall, reticular DFs exhibited a greater sensitivity to light treatment at the level of gene expression than did papillary DFs, with more genes significantly up- or down- regulated. At the intra-cellular signaling pathway level, the up- or down- regulation of vital pathways was observed only for reticular DF, after treatment with 30 J/cm of blue light. At the cellular level, short visible wavelengths exerted a greater inhibitory effect on reticular DF. Several genes involved in the TGF-β signaling pathway were also affected. In addition, procollagen I production was inhibited. By contrast, 850 nm near-infrared (NIR) light (20 J/cm ) exerted a stimulatory metabolic effect in these cells, with no detectable intracellular ROS formation. Here too, reticular DF were more responsive than papillary DF. This stimulatory effect was only observed under in vivo-like low oxygen conditions, corresponding to normal dermal tissue oxygen levels (approximately 2%).
Conclusion: This study highlights a differential impact of light on human skin cells with upregulation of metabolic activity with NIR light, and inhibition of pro-collagen production and proliferation in response to blue light. These findings open-up new avenues for developing therapies for different cutaneous conditions (e.g., treatment of keloids and fibrosis) or differential therapy at distinct stages of wound healing. Lasers Surg. Med. 50:859-882, 2018. © 2018 Wiley Periodicals, Inc.
6.
Li WH, Seo I, Kim B, et al.
International Journal of Cosmetic Science. 2021;43(3):311-320. doi:10.1111/ics.12698.
Objective: Light therapy has attracted medical interests as a safe, alternative treatment for photo-ageing and photo-damaged skin. Recent research suggested the therapeutic activity of red and infrared (IR) lights may be effective at much lower energy levels than those used clinically. This study was to evaluate the efficacy of low-level red plus near IR light emitting diode (LED) combination on collagen and elastin and ATP production.
Methods: Human dermal fibroblasts or skin tissues were irradiated daily by red (640 nm) plus near IR (830 nm) LED lights combination at 0.5 mW/cm for 10 minutes (0.3 J/cm ). qPCR, ELISAs or histology were used to determine the gene and protein expressions. Fluorescent measurement was used to assess crosslinks of collagen and elastic fibres. ATP production was evaluated by ATP assay.
Results: Treatment of human fibroblast cell cultures with low-level red plus near IR lights combination was found to significantly increase LOXL1, ELN and COL1A1 and COL3A1 gene expressions as well as the synthesis of the procollagen type I and elastin proteins. Treating human skin explants with low-level red plus near IR lights combination similarly induced significant increases in the same gene expressions, type III collagen and elastic fibre formation and crosslinks. ATP production was increased in human dermal fibroblasts after red plus near IR lights combination treatment.
Conclusion: Low-level red plus near IR lights combination stimulated the production of collagen and elastin production associated with anti-ageing benefits. These findings suggest that low-level red plus near IR LED light combination may provide an effective treatment opportunity for people with photo-aged skin.
7.
Kim SK, You HR, Kim SH, et al.
Clinical and Experimental Dermatology. 2016;41(7):798-805. doi:10.1111/ced.12902.
Background: Red-coloured light-emitting diodes (LEDs) can improve skin photorejuvenation and regeneration by increasing cellular metabolic activity.
Aim: To evaluate the effectiveness of visible LEDs with specific wavelengths for skin photorejuvenation in vitro and in vivo.
Methods: Normal human dermal fibroblasts (HDFs) from neonatal foreskin were cultured and irradiated in vitro by LEDs at different wavelengths (410-850 nm) and doses (0-10 J/cm(2) ). In vivo experiments were performed on the skin of hairless mice. Expression of collagen (COL) and matrix metalloproteinases (MMPs) was evaluated by semi-quantitative reverse transcription PCR (semi-qRT-PCR), western blotting and a procollagen type I C-peptide enzyme immunoassay (EIA). Haematoxylin and eosin and Masson trichrome stains were performed to evaluate histological changes.
Results: In HDFs, COL I was upregulated and MMP-1 was downregulated in response to LED irradiation at 595 ± 2 and 630 ± 8 nm. In the EIA, a peak result was achieved at a dose of 5 J/cm(2) with LED at 595 ± 2 nm. In vivo, COL I synthesis was upregulated in a dose-dependent manner to both 595 and 630 nm LED irradiation, and this effect was prolonged to 21 days after a single irradiation with a dose of 100 J/cm(2) . These histological changes were consistent with the results of semi-qRT-PCR and western blots.
Conclusion: Specific LED treatment with 595 ± 2 and 630 ± 8 nm irradiation was able to modulate COL and MMPs in skin, with the effects persisting for at least 21 days after irradiation. These findings suggest that yellow and red LEDs might be useful tools for skin photorejuvenation.
8.
Photobiomodulation Response From 660 nm Is Different and More Durable Than That From 980 nm.
Fuchs C, Schenk MS, Pham L, et al.
Lasers in Surgery and Medicine. 2021;53(9):1279-1293. doi:10.1002/lsm.23419.
Background And Objectives: Photobiomodulation (PBM) therapy uses light at various wavelengths to stimulate wound healing, grow hair, relieve pain, and more-but there is no consensus about optimal wavelengths or dosimetry. PBM therapy works through putative, wavelength-dependent mechanisms including direct stimulation of mitochondrial respiration, and/or activation of transmembrane signaling channels by changes in water activity. A common wavelength used in the visible red spectrum is ~660 nm, whereas recently ~980 nm is being explored and both have been proposed to work via different mechanisms. We aimed to gain more insight into identifying treatment parameters and the putative mechanisms involved.
Study Design/materials And Methods: Fluence-response curves were measured in cultured keratinocytes and fibroblasts exposed to 660 or 980 nm from LED sources. Metabolic activity was assessed using the MTT assay for reductases. ATP production, a major event triggered by PBM therapy, was assessed using a luminescence assay. To measure the role of mitochondria, we used an ELISA to measure COX-1 and SDH-A protein levels. The respective contributions of cytochrome c oxidase and ATP synthase to the PBM effects were gauged using specific inhibitors.
Results: Keratinocytes and fibroblasts responded differently to exposures at 660 nm (red) and 980 nm (NIR). Although 980 nm required much lower fluence for cell stimulation, the resulting increase in ATP levels was short-term, whereas 660 nm stimulation elevated ATP levels for at least 24 hours. COX-1 protein levels were increased following 660 nm treatment but were unaffected by 980 nm. In fibroblasts, SDH-A levels were affected by both wavelengths, whereas in keratinocytes only 660 nm light impacted SDH-A levels. Inhibition of ATP synthase nearly completely abolished the effects of both wavelengths on ATP synthesis. Interestingly, inhibiting cytochrome c oxidase did not prevent the rise in ATP levels in response to PBM treatment.
Conclusion: To the best of our knowledge, this is the first demonstration of differing kinetics in response to PBM therapy at red versus NIR wavelength. We also found cell-type-specific differences in PBM therapy response to the two wavelengths studied. These findings confirm that different response pathways are involved after 660 and 980 nm exposures and suggest that 660 nm causes a more durable response. © 2021 Wiley Periodicals LLC.
9.
The Effect of Red-to-Near-Infrared (R/Nir) Irradiation on Inflammatory Processes.
Walski T, Dąbrowska K, Drohomirecka A, et al.
International Journal of Radiation Biology. 2019;95(9):1326-1336. doi:10.1080/09553002.2019.1625464.
Near-infrared (NIR) and red-to-near-infrared (R/NIR) radiation are increasingly applied for therapeutic use. R/NIR-employing therapies aim to stimulate healing, prevent tissue necrosis, increase mitochondrial function, and improve blood flow and tissue oxygenation. The wide range of applications of this radiation raises questions concerning the effects of R/NIR on the immune system. In this review, we discuss the potential effects of exposure to R/NIR light on immune cells in the context of physical parameters of light. The effects that R/NIR may induce in immune cells typically involve the production of reactive oxygen species (ROS), nitrogen oxide (NO), or interleukins. Production of ROS after exposure to R/NIR can either be inhibited or to some extent increased, which suggests that detailed conditions of experiments, such as the spectrum of radiation, irradiance, exposure time, determine the outcome of the treatment. However, a wide range of immune cell studies have demonstrated that exposure to R/NIR most often has an anti-inflammatory effect. Finally, photobiomodulation molecular mechanism with particular attention to the role of interfacial water structure changes for cell physiology and regulation of the inflammatory process was described. Optimization of light parameters allows R/NIR to act as an anti-inflammatory agent in a wide range of medical applications.
10.
Photobiomodulation CME Part I: Overview and Mechanism of Action.
Maghfour J, Ozog DM, Mineroff J, et al.
Journal of the American Academy of Dermatology. 2024;91(5):793-802. doi:10.1016/j.jaad.2023.10.073.
New Research
Photobiomodulation (PBM), previously known as low-level laser light therapy, represents a noninvasive form of phototherapy that utilizes wavelengths in the red light (RL, 620-700 nm) portion of the visible light (VL, 400-700 nm) spectrum and the near-infrared (NIR, 700-1440 nm) spectrum. PBM is a promising and increasingly used therapy for the treatment of various dermatologic and nondermatologic conditions. Photons from RL and NIR are absorbed by endogenous photoreceptors including mitochondrial cytochrome C oxidase (COX). Activation of COX leads to the following changes: modulation of mitochondrial adenosine triphosphate (ATP), generation of reactive oxygen species (ROS), and alterations in intracellular calcium levels. The associated modulation of ATP, ROS and calcium levels promotes the activation of various signaling pathways (eg, insulin-like growth factors, phosphoinositide 3-kinase pathways), which contribute to downstream effects on cellular proliferation, migration, and differentiation. Effective PBM therapy is dependent on treatment parameters (eg, fluence, treatment duration and output power). PBM is generally well-tolerated and safe with erythema being the most common and self-limiting adverse cutaneous effect.
11.
Biological Effects and Medical Applications of Infrared Radiation.
Tsai SR, Hamblin MR.
Journal of Photochemistry and Photobiology. B, Biology. 2017;170:197-207. doi:10.1016/j.jphotobiol.2017.04.014.
Infrared (IR) radiation is electromagnetic radiation with wavelengths between 760nm and 100,000nm. Low-level light therapy (LLLT) or photobiomodulation (PBM) therapy generally employs light at red and near-infrared wavelengths (600-100nm) to modulate biological activity. Many factors, conditions, and parameters influence the therapeutic effects of IR, including fluence, irradiance, treatment timing and repetition, pulsing, and wavelength. Increasing evidence suggests that IR can carry out photostimulation and photobiomodulation effects particularly benefiting neural stimulation, wound healing, and cancer treatment. Nerve cells respond particularly well to IR, which has been proposed for a range of neurostimulation and neuromodulation applications, and recent progress in neural stimulation and regeneration are discussed in this review. The applications of IR therapy have moved on rapidly in recent years. For example, IR therapy has been developed that does not actually require an external power source, such as IR-emitting materials, and garments that can be powered by body heat alone. Another area of interest is the possible involvement of solar IR radiation in photoaging or photorejuvenation as opposites sides of the coin, and whether sunscreens should protect against solar IR? A better understanding of new developments and biological implications of IR could help us to improve therapeutic effectiveness or develop new methods of PBM using IR wavelengths.
12.
van der Vloet L, Ducarne Z, Heeren RMA, Berends AC, Vandenbosch M.
Journal of Biotechnology. 2024;396:53-61. doi:10.1016/j.jbiotec.2024.10.009.
New Research
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Core mechanism & dosing
Photobiomodulation CME Part I: Overview and Mechanism of Action. J Am Acad Dermatol. 2024.
PubMed • Journal pageBiphasic Dose Response in Low-Level Light Therapy (LLLT). Dose-Response. 2011.
PubMed • Publisher/DOI
Skin / collagen & cell studies
Low-level red + near-IR lights increase collagen & elastin (in vitro). Int J Cosmetic Sci. 2021.
PubMed • Publisher/DOIDifferential response of human dermal fibroblasts to visible & NIR light. Lasers Surg Med. 2018.
PubMed • Publisher/DOISkin photorejuvenation: yellow vs red LEDs (in vitro & in vivo). Clin Exp Dermatol. 2016.
PubMed • Publisher/DOI
Wound/tissue repair (preclinical wavelength comparison)
Effect of red & NIR wavelengths on healing of dermal abrasion in mice (635/810 vs 730/980 nm). Lasers Med Sci. 2014.
PubMed • Free full text (PMC)
Circulation & nitric-oxide signalling
Red light–activated vasodilation via NO precursor (in vivo). Frontiers in Physiology. 2022.
Free full text • PMCPhotobiomodulation and nitric-oxide signalling (review). Nitric Oxide. 2023.
PubMed
Immune/inflammation
The effect of red-to-near-infrared irradiation on inflammatory processes (review). Int J Radiat Biol. 2019.
PubMed • Publisher/DOI
Sport, recovery & performance
LLLT/PBM for acute tissue injury or sport performance (narrative review). Sports (MDPI). 2024.
Free full text • PMCPBM & exercise-induced oxidative stress (systematic review & meta-analysis). Antioxidants (MDPI). 2022.
Free full textPBM and running performance (meta-analysis). Int J Exercise Sci. 2024.
Free full text (PMC)Acute dose–response of PBM on 5-km running (LEDs; RCT). J Pain Res. 2024.
PubMed
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