What Is Red Light Therapy and How Does It Work?

Red light therapy is the use of low-power red and near-infrared light, usually from LEDs and sometimes from lasers, shone on the skin for a few minutes at a time. Its medical name is photobiomodulation. It works through the light itself, not through heat, and it contains no ultraviolet. The leading explanation for how it works is that the light is absorbed inside the mitochondria, the parts of a cell that produce its energy, and that this changes how the cell behaves for a while afterwards. The better-tested uses are fine lines, mild to moderate acne when red is paired with blue light, and some kinds of pain treated with clinic lasers. Results build over weeks of repeated sessions, and dermatologists say the details of how it works are not yet fully understood. This article explains the names, where the idea came from, what the light does in the body, and what red light therapy is often confused with.

What is red light therapy?

It is a treatment that shines red light, near-infrared light or both on the body at low power. The American Academy of Dermatology describes it as non-invasive and gives photobiomodulation as its other name.

The AAD's page is a good short overview. Red light is the visible part, roughly 620 to 700 nm. Near-infrared, from about 800 nm upwards, cannot be seen. The devices range from masks, wands and panels at home to beds in gyms and lasers in clinics. UCLA Health. The same therapy has been sold under several names, which is a large part of the confusion.

The Cleveland Clinic lists most of these as other names for red light therapy. Cleveland Clinic. Cold laser therapy vs red light therapy explains what separates a laser from an LED.

What does red light therapy do?

In trials it has softened fine lines, calmed inflamed acne when used with blue light, and eased some neck and knee pain. The strength of the evidence differs a great deal from one use to the next.

Examples of the trials behind those rows: a split-face trial of 76 people for wrinkles, a Lancet analysis of 16 neck pain trials, and the mucositis guideline. Lee 2007, Chow 2009, Zadik 2019. Red light therapy has not been shown to cause weight loss or remove cellulite; the Cleveland Clinic says there is no scientific evidence for either. Red light therapy benefits gives the numbers for each use, and does red light therapy work looks at the placebo question.

How does red light therapy work?

The leading explanation is that red and near-infrared light is absorbed by an enzyme in the mitochondria, the cell makes energy more efficiently for a while, and signals follow that change what the cell does. It is a working theory built mostly on cell and animal studies.

1. Absorption. The reviews name an enzyme in the mitochondria, cytochrome c oxidase, as one of the most important absorbers of this light.
2. More cell energy. A rise in ATP, the molecule cells use as fuel, is one of the most frequent findings in laboratory studies.
3. Signals. A brief burst of reactive oxygen species, a release of nitric oxide and changes in calcium follow. These are thought to switch on genes, including ones involved in making collagen and in calming inflammation.
4. Blood flow. Nitric oxide widens blood vessels, which may explain the increased circulation seen in treated tissue.

Sources: de Freitas and Hamblin 2016, Hamblin 2017, Chung 2012. The reviews themselves call the nitric oxide step a hypothesis, and researchers are still debating which molecules absorb the light, especially above 1000 nm, where water in the cell has been proposed as the absorber. The AAD puts it in one sentence: "We still do not fully understand the effects of red light on the skin."

One point is built into the definition. The effect is a response to the light and not to heat, which is how the US National Library of Medicine defines low-level light therapy. NLM.

Why red and near-infrared, and not other colours?

Because those wavelengths travel furthest into tissue. Blood and the skin pigment melanin absorb light shorter than about 600 nm, and water absorbs light much longer than 1100 nm.

Between the two lies what researchers call the optical window, roughly 600 to 1100 nm, where light is absorbed least on its way in. Huang 2009. A dermatology review of LED devices gives these depths.

Source: Opel 2015. Treat these as rough guides: depth changes with the power of the device, skin tone and the part of the body. In practice red suits the skin itself and near-infrared reaches the tissue beneath it. 660 nm vs 850 nm covers the practical choice, and LED light therapy colours covers the other colours.

What is photobiomodulation?

It is the scientific name for red light therapy, agreed by researchers in 2015. It means using light to change how cells work, without heat.

The editorial that proposed the name defined it as light therapy using lasers, LEDs or broadband light in the visible and infrared range, acting through a non-thermal process. Anders 2015. Two reasons were given for dropping "low-level laser therapy": nobody could say what "low" meant, and LEDs had turned out to work too, so "laser" no longer fitted. The US National Library of Medicine added the term to its index for the 2016 edition. If a clinic offers photobiomodulation and a gym offers red light therapy, they are describing the same kind of light.

Where did red light therapy come from?

From a laser experiment on mice in Budapest in 1967, and from LED research funded by NASA in the 1990s.

Endre Mester, at Semmelweis University, was studying a low-powered ruby laser (694 nm) and cancer in mice. The laser did not do what he was testing for, but the shaved hair grew back faster on the treated animals, and wound healing became one of the first uses his group studied. Huang 2009, Chung 2012. For the next few decades the field used lasers.

LEDs arrived through plant science. A company working with NASA built LED units for growing plants, one of which grew potatoes on the space shuttle in 1995. Scientists working under the lights noticed that scrapes on their hands seemed to heal faster, and NASA then funded medical research on the LEDs by the neurologist Harry Whelan from 1995 to 2003. NASA's own account adds that the agency did not end up using the technology in space. NASA Spinoff. What the LED work did do was make large, affordable light sources possible, and with them home devices.

How is the dose measured?

By two numbers: irradiance, which is how much light lands on each square centimetre of skin, and fluence, which is irradiance multiplied by time.

• Irradiance is given in mW/cm². Some makers quote W/m² instead; 10 W/m² is 1 mW/cm².
• Fluence, the dose, is given in J/cm². Multiply mW/cm² by the seconds and divide by 1,000. A device giving 20 mW/cm² for 10 minutes delivers 12 J/cm².
• More is not better. In cell and animal experiments, too little light does nothing and too much stops helping, a pattern researchers call the biphasic dose response. It is assumed to apply to people as well. Huang 2009.

There is no single agreed dose. Harvard Health notes that scientists have not yet pinned down how long a session should last. Harvard Health. That is why the practical rule is to follow the timer and limits of the device you have. Red light therapy at home works through the arithmetic.

What is red light therapy not?

It is not ultraviolet, not a tanning bed, not a sauna and not a laser that resurfaces skin. Each of those works in a different way.

Sources: Mayo Clinic on saunas, Mayo Clinic on light boxes, Johns Hopkins Medicine. More on each: red light beds and sunbeds, red light therapy vs SAD lamps, blue light therapy and red light and cancer.

What does a session involve?

A few minutes in front of or under the light, on bare skin, repeated several times a week.

The AAD says it is not a one-off treatment and that results take time. The Cleveland Clinic describes clinic courses of one to three sessions a week for weeks or months, and Harvard Health says home devices need to be used several times a week for four to six months. Sessions in trials were short: in one sham-controlled trial of a home mask they lasted nine minutes, five times a week. Do red light masks work has the details, how often to use red light therapy covers frequency, and how long it takes to work covers timelines.

Is red light therapy safe?

Used as directed it appears to be safe in the short term, according to the AAD and the Cleveland Clinic. Nobody has followed home users for many years.

• Reported side effects are mild: temporary pain or irritated skin.
• Eyes. Use the eye protection the device's directions call for. Do you need goggles explains when.
• Avoid it, or ask a doctor first, if you take medication that makes you sensitive to light or have a light-sensitive condition. The AAD also advises people with darker skin tones to speak to a dermatologist first, because darker skin is more sensitive to visible light.

Is red light therapy safe goes through the side effects and who should not use it.

Where do Kivorla devices fit?

Both are home devices that use red and near-infrared light, with blue as a separate option. Both state their wavelengths and their output.

The 4-Wavelength Red Light Therapy Mask runs 665 nm red with 850 and 1064 nm near-infrared in one mode and 460 nm blue with 850 nm in the other, at 50 to 103 mW/cm², with a timer of 5, 10 or 15 minutes. The 9-Spectrum Red Light Therapy Panel has nine wavelengths from 480 to 1060 nm, each dimmable, and delivers at least 1567 W/m² at six inches, with a timer of 1 to 30 minutes and goggles in the box. Neither has been through its own clinical trial; the studies above tell you what this kind of light can do.

Read the precautions before ordering, since returns are accepted within 30 days, less a 10% restocking fee if the device is unopened with its seals intact, or 20% if it is opened but undamaged and complete. Standard shipping to the US, UK and Germany is free.

Kivorla devices are general wellness devices, not medical devices. If you have a medical condition, speak to your doctor before using a light device.