Cozy Butter · Free tool · Skin and hair
Light masks and caps come with a lot of colours and a lot of claims. Tap each colour to see what it was actually tested for and what the studies found, check what a device label should tell you, and work out the dose a device gives.
Every figure on this page was checked against the original study, the FDA, or the American Academy of Dermatology.
"Some evidence" means several small controlled trials pointing the same way. None of these colours has the large, independent trials that would make it a sure thing.
Hair is where light therapy has its best research, but only for one kind of hair loss. Pick the one that sounds like you.
This is the slow, genetic thinning at the crown, hairline or part, called androgenetic alopecia. Caps and helmets around 650 to 660 nm were tested against fake devices in several trials. In one small trial, men using a 655 nm helmet every other day for 16 weeks saw hair counts rise by about 67%, compared with about 28% on a placebo helmet. A matching trial in women found about 48%, compared with 11%. Men, women. Four trials of a laser comb used over 26 weeks also beat a sham comb. Source. A 2024 review of 38 studies, almost all in pattern hair loss, found a benefit over placebo, with results varying a lot from study to study. Source.
It helps some people, modestly, with months of steady use. It does not cure pattern hair loss.
Losing a lot of weight can push many hairs into their resting phase at once, a type of shedding called telogen effluvium. The American Academy of Dermatology lists losing 20 pounds or more as a trigger. It usually shows up a few months after the change. As your body adjusts the shedding stops, and hair tends to regain its normal fullness within 6 to 9 months. If the cause keeps going, shedding can last longer. Source. In people who had weight-loss surgery, hair loss was more common in those with low zinc, low folate or low stored iron (ferritin). That does not prove these cause it, but they are worth checking with your clinician, along with getting enough protein. Source. If shedding lasts longer than 6 to 9 months, or you see bald patches, see a doctor. The protein calculator can help with a daily target.
The dose is power multiplied by time. Find the power on the device label in mW/cm², enter how long a session lasts, and see how it compares with the trials.
Dose per session
The laser comb hair trials (Jimenez 2014) did not state their dose this way.
Treat the label number with some care. It is usually measured by the seller, and how far the lights sit from your skin changes how much reaches it. Huang, 2009, explains why more light is not always better. Source. Trial doses: Avci, 2013.
Open the listing for a mask or cap you are looking at, and tick what it actually shows.
Light masks and caps go through the FDA’s 510(k) process. The company shows its device is as safe and effective as one already on the market, and the FDA “clears” it. That is a comparison with an existing device, and some of these clearances were granted without any new clinical testing. Source. “Approved” is a stricter route that requires scientific evidence the device is safe and effective for its use, and light masks do not go through it. Source.
The FDA does not approve dietary supplements before they are sold. The company is responsible for their safety and claims. Source. So a cleared device has had a check before sale, which is more than a supplement gets, and it may never have been tested in people.
A real clearance has a number that starts with K. Search it in the FDA 510(k) database and check that the model and the lights listed (colours and nm) match the one you are buying. The clearance is often in the factory’s name, not the brand’s. “FDA registered” is not the same as cleared, and a device sold as “FDA approved” is a warning sign.
Most light masks sold online, cheap and expensive, are made in China, often by the same factory that holds the FDA clearance. We found no published evidence that cheaper devices use dangerous materials. The useful questions are whether the listing states its wavelengths and power, and whether its clearance checks out.
Check with your clinician before you start if you take a medicine that makes you sensitive to light or have an eye condition. Stop and ask if you notice eye discomfort, burning, or new dark patches on your skin.