Red Light Therapy Research Analysis

Q: How are red and near-infrared light different?

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.

Q: Can sun exposure function as a form of red light therapy?

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.

Q: Is red light therapy beneficial for exercise performance and recovery?

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).

Q: Is red light therapy beneficial for skin health and appearance?

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.

Morgan Pfiffner

Red Light Therapy

•Last Updated: October 24, 2023

Red light therapy refers to the practice of exposing the body to light in the red and near-infrared (NIR) spectrum with the goal of producing health benefits. Red light therapy can be beneficial for hair loss, joint pain, and childhood myopia.

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Red Light Therapy is most often used for

Morgan Pfiffner, MS

Nick Milazzo, MSc, MPH

Last Updated:October 24, 2023

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Frequently asked questions
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References

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.

How are red and near-infrared light different?

Can sun exposure function as a form of red light therapy?

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]

Is red light therapy beneficial for exercise performance and recovery?

Is red light therapy beneficial for skin health and appearance?

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?

Note that Red Light Therapy is also known as:

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.