Red Light Therapy for Hair Growth: What the Trials Left Out

Red light therapy for hair growth can add a modest amount of hair in female pattern hair loss, after four to six months of regular sessions. The catch is who it was tested on: small, industry-funded trials that left out the deepest skin tones and counted hair on clipped scalp.

If your part has been getting wider and a laser cap keeps showing up in your feed, you've probably seen the before-and-after photos and the price. Before you buy one, it helps to know whether the women in the trials look anything like you.

Does Red Light Therapy Work for Hair Growth?

For pattern hair loss, there's a measurable effect in trials, but it's small and women don't always notice it. For other kinds of hair loss, the evidence is too thin to say.

The devices shine red light, from lasers or LEDs, onto the scalp. The medical name is low-level laser therapy. The 2014 study most often quoted ran four trials of a laser comb, randomizing 141 women and 128 men with pattern hair loss.

After 26 weeks, women using a 9-beam comb gained about 20 hairs per square centimeter, against about 3 with a sham comb. A 12-beam model gave almost the same result. In the 9-beam trial, women rated their hair as better. In the 12-beam trial, the difference in their own ratings wasn't significant.

A smaller trial tested a helmet with red lasers and LEDs in 42 women who finished the study. After 16 weeks, hair counts rose 48% in the active group and 11% with a sham helmet.

A Cochrane review of female pattern hair loss treatments pooled two laser comb trials with 141 women. Hair counts went up compared with sham, but according to the participants, the laser comb was not more effective than the fake device. The reviewers rated the hair count evidence as low quality.

Who Was Studied in the Red Light Hair Trials?

Women with lighter skin types, mostly white where race was reported, aged 18 to 61, with early to moderate pattern thinning. Here is what the two main trials in women looked like.

• Laser comb trials (2014): only Fitzpatrick skin types 1 to 4 were allowed, and 94.7% of participants were white. Hair at the 1 inch (25 mm) test square was clipped and the spot tattooed so it could be found again. The device maker partly funded the study and supplied the devices, and some authors received fees from it.
• Helmet trial (2014): again skin types 1 to 4 only, ages 18 to 60. Hair at the test site was trimmed to about 1/8 inch (3 mm) and had to be free of gel or spray. It was funded by the helmet's maker, and two authors reported consulting fees and ownership interests in the company.

Fitzpatrick types 5 and 6, the deepest brown and black skin tones, weren't included in either trial. So these trials can't tell you whether the results hold for darker skin.

The hair was counted on short, clipped scalp, too. Neither trial measured growth under long, dense or coily hair, braids or locs. Whether as much light reaches the scalp through them is unknown.

Industry money doesn't make a result wrong. It does mean the strongest numbers come from companies with a stake in them, and that's worth weighing against the price.

What Does FDA Cleared Mean for a Hair Laser?

It means the FDA accepted that the device is as safe and effective as a similar one already on the market. It doesn't necessarily mean the device was tested in its own clinical trial.

A device described as cleared has usually gone through a 510(k) submission, which compares a new device with an existing "predicate" device. The FDA says the supporting data can include clinical data and non-clinical bench testing. Premarket approval (PMA) is a separate route.

So "FDA cleared" on a cap tells you it is substantially equivalent to a device already legally on the market. It doesn't tell you how much hair it grew, or in whom. When the 2014 trials ran, the comb was FDA-cleared for men's hair loss only. The authors note the FDA had screened it for safety, not efficacy.

How Long Does Red Light Therapy Take to Work for Hair?

Plan on at least four to six months of steady use before you judge it. That's the length of the trials, and it adds up to a lot of sessions.

The laser comb trials asked for three sessions a week for 26 weeks. That's 78 sessions of 11 minutes (9-beam) or 8 minutes (12-beam) for the two combs tested in women. The helmet trial asked for 60 sessions of 25 minutes over 16 weeks, or 25 hours under the device.

The trials stopped there, so they can't say what happens after you stop. Mayo Clinic notes that a few small studies show improved hair density, and that more studies are needed to show long-term effects. Treat any device as something you'd use for as long as you want the result.

Is Red Light Therapy Better Than Minoxidil for Women?

Not on the current evidence. Minoxidil has been tested in far more women, and the women using it were more likely to see a difference themselves.

• How many women were studied: the Cochrane review had two laser comb trials with 141 participants. For minoxidil hair counts, it had eight trials with 1,242.
• Change in hair count: about 17 more hairs per square centimeter than sham for the laser comb, and about 13 more than placebo for minoxidil. Both were rated low quality.
• Did women notice? With the laser comb, not clearly more than with sham. With minoxidil, 157 of 593 women reported moderate to marked regrowth, against 77 of 555 on placebo.
• Time: Mayo Clinic says minoxidil takes at least six months, and you keep using it to keep the benefit.

The hair counts look similar, but the laser figure rests on a much smaller group. The American Academy of Dermatology says that not everyone who used a laser saw regrowth. It adds that minoxidil tends to work better alongside another treatment. Ask a dermatologist whether light therapy is a sensible second one for you.

What slows female pattern hair loss covers minoxidil and the prescription options in more detail.

Is Red Light Therapy Safe for Your Scalp and Eyes?

In the trials, side effects were mild and uncommon. Your eyes are the part to protect.

The laser comb trials reported no serious side effects. Dry skin affected 5.1% of users, and itching 2.5%. A few had scalp tenderness, irritation or a warm feeling. The helmet trial reported no side effects.

Cleveland Clinic advises you to shield your eyes for protection with home devices, and says misuse could damage unprotected skin or eyes. It also says the long-term safety of red light devices isn't yet known. What the specs on at-home red light devices mean explains irradiance and FDA labels in more depth.

When to See a Doctor Before Buying a Device

See a doctor first if your hair loss is sudden, patchy, painful or not the slow widening of a part. The trials only tested pattern hair loss, so a device can't help if that isn't what you have.

Mayo Clinic says to see a doctor for sudden or patchy hair loss, or more hair than usual coming out when you comb or wash. It adds that a receding hairline, especially in older women, can be frontal fibrosing alopecia, and that early treatment might help avoid significant permanent hair loss.

Thinning at the crown can also be central centrifugal cicatricial alopecia (CCCA). The AAD says it often affects middle-aged Black women, and it can itch, burn, sting or feel tender. Some people feel nothing at all. CCCA destroys follicles and scar tissue grows over them, so the AAD advises a dermatologist at the first sign of hair loss.

Not sure what's behind your thinning? Start with the main causes of hair loss in women or how to tell shedding from hair loss.

Frequently Asked Questions

Can You Use Red Light Therapy and Minoxidil Together?

Possibly. The AAD says minoxidil tends to work better with another hair loss treatment, though it doesn't name light therapy specifically. Ask a dermatologist before combining them.

Does Red Light Therapy Work Through Braids or Locs?

Nobody knows yet. The trials counted hair on clipped or trimmed scalp, not under braids, locs or dense natural hair. If your thinning is at the edges, why edges thin covers causes a light device won't fix.

How Long Before You See Results From a Laser Cap?

The trials ran for 16 to 26 weeks, with sessions every other day or three times a week. Give it about six months of regular use before you decide.