What is red light therapy?
Red light therapy refers to the practice of exposing the body to red and/or near-infrared light, with the goal of producing health benefits. There is considerable variation in how red light therapy is performed in practice, with differences in factors like the wavelengths of light used, the power intensity (irradiance) of the light, the duration and frequency of exposure, and the regions of the body irradiated.
What are red light therapy’s main benefits?
Red light therapy can reduce pain in a variety of contexts, especially conditions involving joint pain, including knee osteoarthritis,[1] lower back pain,[2] and neck pain.[3] There is also preliminary evidence that red light therapy can reduce pain in fibromyalgia,[4] tendinopathy,[5] rheumatoid arthritis,[6] and headache,[7] as well as during hip surgery recovery.[8]
Red light therapy has been shown to promote hair regrowth in people with hair loss due to androgenic alopecia, with effects seen in both men and women.[9][10] In these studies, the scalp is directly exposed to red light, usually in the 650 to 660 nm range.
Red light therapy has been found to be beneficial for childhood myopia (nearsightedness), slowing its progression and even preventing its occurrence.[11][12][13] Red light therapy may also be helpful for other eye conditions (e.g., macular degeneration, cataracts), but research is still too limited to be certain of its effectiveness.[14][15][16]
Preliminary evidence suggests red light therapy can improve cognitive function in people with dementia[17] and possibly in healthy people as well.[18]
What are red light therapy’s main drawbacks?
Red light exposure to the eye is risky and can result in damage to the retina.[19] For this reason, red light therapy for eye conditions should only be performed under the guidance of a qualified medical professional.
Eye use excluded, red light therapy appears to be fairly safe, with reported side effects tending to be rare and mild (e.g., itchy skin, acne, and skin tenderness).[9] Red light exposure can also produce a sunburn-like effect if the power intensity and duration of exposure are high enough. Interestingly, individuals with darker skin pigmentation appear more susceptible to this effect (unlike with ultraviolet light exposure, where the opposite is true).[20]
How does red light therapy work?
The mechanism by which red light therapy works is not well-established, although most explanations center on its ability to increase cellular energy generation. More specifically, red and near-infrared light are thought to stimulate the activity of the mitochondrial protein cytochrome c oxidase (CCO), which increases ATP production.[21][22] This increase in ATP synthesis can in turn lead to enhanced tissue repair, changes in gene expression, and the generation of cell signaling molecules, all potentially contributing to the biological effects of red light therapy.[21][23]
What are other names for Red Light Therapy
- Photobiomodulation (PBM)
- Low-Level Laser Therapy (LLLT)
- Infrared-Light Therapy
Dosage information
To discuss the dosages used in red light therapy, some important terms need to be covered:
Power intensity (also called irradiance): The amount of power delivered per square centimeter of body area per second, often expressed as mW/cm2/s (milliwatts per square cm).
Power density: The product of power intensity and duration of exposure, often expressed as J/cm2 (joules per square cm).
Total energy (the “dose”): The product of power density and body area exposed, usually expressed as J (joules).
Red light therapy for eye conditions uses the lowest doses, with most studies using power intensities below 1 mW/cm2 for around 3 minutes per session, corresponding to a power density well below 1 J/cm2. Red light therapy for hair loss typically involves power intensities of around 3–90 mw/cm2 for around 15–20 minutes per session, resulting in a power density of around 1–10 J/cm2. Finally, some research suggests the effective dose for knee osteoarthritis is around 4–8 J per spot for light with a wavelength range of 780–860 nm and around 1–3 J per spot for light with a wavelength of 904 nm.
Frequently asked questions
Red light therapy refers to the practice of exposing the body to red and/or near-infrared light, with the goal of producing health benefits. There is considerable variation in how red light therapy is performed in practice, with differences in factors like the wavelengths of light used, the power intensity (irradiance) of the light, the duration and frequency of exposure, and the regions of the body irradiated.
Red light therapy uses either red light, near-infrared light, or a combination of both. But what exactly is the difference between red light and near-infrared light?
All light travels as a wave of electromagnetic radiation, and the distance between wave peaks is known as the wavelength. The color and type of light are characterized by its wavelength.
Red light has wavelengths in the range of about 620–700 nm, while near-infrared light has wavelengths in the range of about 700–1,400 nm. The defining difference between the two types of light is that red light is visible to the human eye and infrared light is not.
Our bodies are mostly impenetrable to visible light, including red light. However, longer-wavelength light (i.e., closer to near-infrared than red) can more readily penetrate deeper into the body.[24][25][26][27] As a result, red light therapy for topical applications (e.g., hair loss, skin health, eyes) will tend to use red light (since a greater proportion of energy is delivered to skin cells), while red light therapy targeting tissues inside the body (e.g., joints, muscles, brain) will tend to use infrared light.
Much of the light emitted by the sun is in the red and near-infrared spectrum. As a result, sunlight exposure might be able to replicate some of the effects of red light therapy.
It’s estimated that unobscured sunlight delivers around 20–40 mW/cm2 of red and near-infrared light (although the amount varies depending on factors like time of day, time of year, and latitude).[28] This puts sunlight in the range of the power densities used in many red light therapy studies.
That said, there isn’t much direct research looking at whether sunlight actually does replicate the health effects of red light therapy, so whether sun exposure can act as a form of red light therapy remains uncertain.
Furthermore, sunlight is a major source of other wavelengths of light as well, which could enhance or inhibit the effects of red light. For example, while exposure to red and infrared light may reduce signs of skin aging (although the evidence for this is weak), the net effect of getting a lot of sunlight exposure is the promotion of skin aging due to the effect of ultraviolet light.[29][30] With that said, it may be worth noting that most sunscreens block UV light while not blocking much red and infrared light (although a small number of sunscreens block both).[31][32][33]
Ultimately, whether the net effect of sunlight is similar to that of red and near-infrared light can’t be assumed.
Red light therapy can reduce pain in a variety of contexts, especially conditions involving joint pain, including knee osteoarthritis,[1] lower back pain,[2] and neck pain.[3] There is also preliminary evidence that red light therapy can reduce pain in fibromyalgia,[4] tendinopathy,[5] rheumatoid arthritis,[6] and headache,[7] as well as during hip surgery recovery.[8]
Red light therapy has been shown to promote hair regrowth in people with hair loss due to androgenic alopecia, with effects seen in both men and women.[9][10] In these studies, the scalp is directly exposed to red light, usually in the 650 to 660 nm range.
Red light therapy has been found to be beneficial for childhood myopia (nearsightedness), slowing its progression and even preventing its occurrence.[11][12][13] Red light therapy may also be helpful for other eye conditions (e.g., macular degeneration, cataracts), but research is still too limited to be certain of its effectiveness.[14][15][16]
Preliminary evidence suggests red light therapy can improve cognitive function in people with dementia[17] and possibly in healthy people as well.[18]
Preworkout red light therapy might improve exercise performance, but more research is needed. Red light therapy has not been shown to reduce delayed onset muscle soreness (DOMS).
Due to its suspected ability to increase cellular energy production, red light therapy has been investigated as an ergogenic aid, with studies typically exposing the working muscle to light immediately before exercise.
Red light therapy has been shown to slightly increase the number of repetition to failure on eccentric exercises (e.g., bicep curls and knee extensions), although this finding is based in large part on studies involving young male volleyball players performed by a single research group.[34]
Only a couple of long-term studies have looked at whether red light therapy can increase strength and muscle gains when added to regular resistance training. One study in young men found red light therapy before strength training led to greater increases in muscle size and strength,[35] whereas a study in older men found it had no benefit.[36] Finally, one study on older women found red light therapy after strength training did not increase muscle strength (muscle size was not reported).[37]
Red light therapy before exercise has sometimes been found to increase performance on predominantly anaerobic activities (e.g., cycling or running to exhaustion)[38][39][40][41] However, this is not a consistent finding.[42][43][44]
Lastly, red light therapy does not seem to reliably reduce muscle soreness in the days following a workout.[45][46][47][47]
Red light therapy might be beneficial for some aspects of skin health and appearance (e.g., acne, wrinkles), but it's hard to say much with certainty due to limited high-quality research.
Red light therapy is sometimes used as a treatment for acne, possibly by reducing inflammation and sebum production.[48] However, most of the research on this topic is not very high-quality (often lacking appropriate control groups, for example).[49][50][51][52][53]
Some research suggests red light therapy can increase the dermal synthesis of collagen and elastin,[54][55] proteins that help maintain skin elasticity and which tend to decrease during aging. Consistent with this, a few clinical trials suggest red light therapy can indeed reduce the appearance of wrinkles,[56] although only a few studies exist, so more research is needed.
Finally, it’s been suggested that red light exposure may make the skin less susceptible to sunburns. The evidence for this draws largely from a single pilot study involving 15 people. In that study, regularly exposing the skin to red light — specifically a wavelength of 660 nm at an intensity of 60 mW/cm2 for 160 seconds — seemed to result in less erythema (redness) in response to UV exposure (although statistical significance was not examined).[57] Subsequent (unpublished) data from the same researcher indicated that this protective effect was greater with near-infrared light than red light. Ultimately, given the preliminary nature of this data, this finding requires replication. And even if red/near-infrared light does in fact have a sunburn-inhibiting effect, it can’t yet be assumed this translates into a reduction in UV-induced DNA damage, meaning that whether red light therapy reduces the risk of skin cancer is unclear.
Red light exposure to the eye is risky and can result in damage to the retina.[19] For this reason, red light therapy for eye conditions should only be performed under the guidance of a qualified medical professional.
Eye use excluded, red light therapy appears to be fairly safe, with reported side effects tending to be rare and mild (e.g., itchy skin, acne, and skin tenderness).[9] Red light exposure can also produce a sunburn-like effect if the power intensity and duration of exposure are high enough. Interestingly, individuals with darker skin pigmentation appear more susceptible to this effect (unlike with ultraviolet light exposure, where the opposite is true).[20]
The mechanism by which red light therapy works is not well-established, although most explanations center on its ability to increase cellular energy generation. More specifically, red and near-infrared light are thought to stimulate the activity of the mitochondrial protein cytochrome c oxidase (CCO), which increases ATP production.[21][22] This increase in ATP synthesis can in turn lead to enhanced tissue repair, changes in gene expression, and the generation of cell signaling molecules, all potentially contributing to the biological effects of red light therapy.[21][23]
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