PRP and Low-Level Laser Therapy for Hair Loss: What the Evidence Shows

Platelet-rich plasma (PRP) injections and low-level laser therapy (LLLT) are two procedures often considered for pattern hair loss alongside medication. Both have been tested in randomized trials, and both come with real gaps in the evidence. The American Academy of Dermatology (AAD) groups at-home laser devices and PRP among emerging or limited-evidence options, and DermNet describes PRP as under investigation and the benefit of LLLT as unproven. This guide looks at what the trials actually show, what FDA clearance means for laser devices, how treatment is usually scheduled and where the limits are.

Platelet-rich plasma

How PRP is prepared

A 2022 review in Drug Design, Development and Therapy describes the process. A small amount of the patient's own blood, roughly 10 to 60 mL, is drawn into tubes containing an anticoagulant and spun in a centrifuge. This separates the blood into layers, and the platelet-rich middle layer is collected and injected into the scalp. The platelet concentration is typically two to six times the normal level in blood.

There is no standard method. The review notes that commercial kits differ in platelet concentration, white blood cell content and whether an activator is added, and there is no agreement on whether activation helps.

What the trials show

A 2023 meta-analysis in Aesthetic Plastic Surgery pooled 10 randomized trials with 318 participants that compared PRP with saline injections in androgenetic alopecia. Its main findings:

• Hair density: PRP increased density by an average of about 25 hairs per square centimetre compared with saline.
• Hair thickness: no significant difference in hair diameter.
• Who benefited most: trials that enrolled only men showed larger effects than mixed trials, and smaller trials showed larger effects than bigger ones. The authors caution that small studies can overestimate benefit.
• Follow-up: the included trials ran for 3 to 6 months, and none assessed results beyond 12 months.

For women, the 2022 review reports mixed findings. One women-specific meta-analysis found that PRP increased hair diameter but not density, and the review notes that evidence on whether sex affects the response is still debated.

Sessions and scheduling

Protocols vary widely between studies. The 2022 review lists these as common regimens:

• Monthly injections for three to four sessions, the pattern used in most trials
• Sessions every two to three weeks, for example four sessions spaced 15 days apart
• Weekly sessions, used in one trial in women

One proposed protocol uses monthly sessions for three months, then a session every three months for the first year. No standard maintenance schedule has been established.

Side effects and who should avoid it

The review describes side effects as generally mild and temporary: pain during the injections, mild headache, minimal itching, and short-lived redness and swelling at the injection sites. No major complications were reported in the studies it reviewed.

It lists these as reasons not to have PRP:

• Absolute: very low platelet count, platelet function disorders, unstable circulation, sepsis or infection at the treatment site
• Relative: anti-inflammatory painkiller (NSAID) use within 48 hours, recent steroid injections at the site or recent oral steroids, a recent illness or fever, cancer, anaemia, a low platelet count and tobacco use

Regulatory status

The 2022 review explains that both the devices used to separate platelets and the PRP product fall under FDA regulation, and that using PRP for anything other than transfusion is off-label. Off-label use is permitted when a physician uses it as part of medical practice. The review lists oral finasteride for men and topical minoxidil as the FDA-approved hair loss treatments, and PRP is not among them.

Low-level laser therapy

What the devices are

LLLT devices shine low-power red light onto the scalp. A 2021 systematic review in the Journal of Clinical and Aesthetic Dermatology found 32 home-use devices marketed in the US as of January 2020, in four designs: caps, helmets, combs and headbands. Most used laser diodes, and most emitted light between 620 and 678 nm, typically around 650 to 655 nm.

The power involved is low: one device described in an FDA filing uses diodes rated below 5 mW each. Lasers used to resurface skin are a different group of devices.

What FDA clearance means

Home laser devices for hair loss are cleared through the FDA's 510(k) pathway. The clearance letter for one such device (K222477, issued in November 2022) shows how this works:

• Regulation: 21 CFR 890.5500, regulation name "Infrared Lamp", Class II, product code OAP ("Laser, Comb, Hair")
• Basis: the FDA found the device "substantially equivalent" to devices already legally on the market
• Indication: to promote hair growth in men with androgenetic alopecia at Hamilton-Norwood stages IIa to V and women at Ludwig-Savin stages I to II, with Fitzpatrick skin types I to IV, sold over the counter
• Testing submitted: the summary lists non-clinical testing, such as biocompatibility and electrical safety

So "FDA-cleared" means the agency accepted that a device is similar enough to an earlier one. It is a different standard from FDA approval of a drug. The letter also notes that a substantial equivalence determination does not mean the FDA has found the device compliant with every other legal requirement.

What the trials show

The 2021 review pooled seven double-blind, sham-controlled trials with 607 participants. Devices increased hair density more than sham devices, with similar effects in men and women. Devices using only laser diodes showed a larger effect than those combining lasers with LEDs.

Sessions

Most devices in the review were used three to four times a week, with sessions lasting from 90 seconds to 36 minutes, a median of 30 minutes. One device was used daily.

Side effects

Reported side effects were generally mild, including tingling, hives, headache, dry skin, itching and scalp tenderness. Some trials reported none.

How the two compare

The limits of the evidence

For PRP, the meta-analysis found substantial variation between trials, linked to small sample sizes, sex, hair loss stage and differing preparation methods, and too few trials in women. The 2022 review adds that many studies were small, uncontrolled or non-randomized, and that some found PRP ineffective. For LLLT, the 2021 review notes short follow-up, small trials, varied wavelengths and power, no head-to-head device comparisons and data limited to mild to moderate hair loss.

Because the laser trials covered only mild to moderate hair loss, results in more advanced hair loss are unknown. Both treatments are worth discussing with a dermatologist alongside the FDA-approved options, oral finasteride for men and topical minoxidil.