PRP, Microneedling and Laser Caps: What the Evidence Actually Supports

Finasteride and minoxidil are the two treatments with regulatory approval behind them. Everything else sold for hair loss sits somewhere on a spectrum from genuinely promising to actively deceptive, and the marketing does not distinguish. This is an attempt to sort them by what the evidence actually supports, including the ones where the honest answer is nothing.

Microneedling

A roller or pen studded with fine needles is passed over the scalp, producing controlled micro-injury. The proposed mechanisms are a wound-healing response that activates follicular stem cells, and improved penetration of anything applied topically afterwards.

A 2025 meta-analysis pooled 12 randomised trials and 631 patients. On hair count, the combination of microneedling and topical minoxidil beat minoxidil alone with a standardised mean difference of 1.32 (95% CI 0.73 to 1.92, P < 0.01). On hair diameter it was 0.34 (0.11 to 0.58), a smaller but more consistent effect with no heterogeneity at all.

The single most important fact about this literature is easy to miss: not one of those 12 trials tested microneedling on its own. Every study compared microneedling plus minoxidil against minoxidil alone. There is essentially no controlled evidence that microneedling by itself grows hair, and the most plausible mechanism requires the drug to be there.

Two further caveats. Heterogeneity on the hair count result was 88 percent, and every included study carried “some concern” for risk of bias, mostly around allocation concealment and the use of patient self-assessment as an outcome. No trial was rated low risk.

On technique, the review found no significant difference between needle depths at or below 1 mm and those above it, no difference between treatment durations, and no difference between roller and electrodynamic devices. Most trials used weekly or fortnightly sessions alongside 5 percent minoxidil twice daily. Adverse events were mild and self-limiting, mostly scalp itching, at 74 events against 59 in the minoxidil-only arms.

Platelet-rich plasma

Blood is drawn, spun in a centrifuge to concentrate the platelets, and the resulting plasma is injected into the scalp. The rationale is that platelet growth factors stimulate follicles.

The headline number is impressive. A meta-analysis of 14 randomised trials and 431 patients found a mean difference of 27.55 hairs per square centimetre (14.04 to 41.06) in favour of PRP.

The number underneath it is the problem. Heterogeneity was 95.99 percent. That is not variation around a common effect; that is trials measuring different things and arriving at incompatible answers. The pooled figure is an average of results that do not belong in the same average.

The reason is that PRP is not a drug with a defined dose. It is a procedure, and the procedure is not standardised.

Note that trials report centrifuge force in two units that cannot be converted into one another without knowing the rotor, which is itself a symptom of how unstandardised this field is.

On hair diameter, the same analysis found a mean difference of 2.02 micrometres with a confidence interval of minus 0.85 to 4.88, which crosses zero. PRP has not been shown to thicken hair. A separate analysis of 9 trials and 238 patients reached the same conclusion, finding improved density but no significant difference in hair count or diameter. A third, much larger review covering 41 trials and 1,877 participants found activated PRP increased density but did not significantly affect thickness, and rated the overall evidence as moderate.

The certainty ratings from the first analysis were low for hair density and very low for hair diameter, with funnel plot asymmetry suggesting publication bias, though a formal test for it was not significant.

The fair summary is that PRP probably does something to density, that nobody can tell you how much because it depends on a protocol your clinic has not standardised either, and that you should ask what centrifugation protocol and activation method they use before paying for a course.

Laser caps, and what “FDA cleared” means

This distinction does more work than any efficacy figure, so take it first.

A drug is FDA approved after trials demonstrate safety and efficacy. A device can be FDA cleared through a 510(k) submission, which requires the manufacturer to show only that the device is substantially equivalent to one already on the market. It does not require a new clinical trial. The American Academy of Dermatology states the position plainly: the requirements for getting FDA cleared are much less stringent than for getting FDA approved.

A concrete example. The iRestore Hair Growth System was cleared in January 2016 under submission K151662. The submission contained no original clinical performance data for the device itself; the applicant relied on published trials of an earlier device it resembled. Between 2000 and 2018, 47 low-level laser devices received 510(k) clearance by this route. The authors who catalogued them concluded that marketed indications have not been adequately explored and that devices currently on the market have the potential to mislead consumers.

The effect itself is real but modest. A meta-analysis of 8 studies comprising 11 double-blind randomised trials found a standardised mean difference of 1.316 (0.993 to 1.639) for hair density against sham. Lower treatment frequency performed better than higher, at 1.555 against 0.949, which is not what an intuitive dose-response would predict.

The quality limits matter. Trials ranged from 40 to 269 subjects, maximum follow-up was 26 weeks, there are no head-to-head comparisons with established treatments, and many studies were manufacturer-sponsored. Most telling: of 32 FDA-cleared home-use devices identified, only four had any published randomised trial behind them at all.

So a laser cap is plausibly worth something, the specific cap you are being sold probably has no trial behind it, and “FDA cleared” on the box tells you nothing about whether it works.

Topical finasteride

The appeal is obvious: the efficacy of finasteride with less systemic exposure. The trial data support about half of that.

A phase III trial in 458 patients found target area hair count rose by an adjusted mean of 20.2 hairs at week 24 against 6.7 with placebo (P < 0.001), an effect similar to oral finasteride. Plasma finasteride concentrations were more than 100 times lower than with the oral drug.

Here is the caveat that gets left out. Serum DHT still fell by 34.5 percent with the topical formulation, against 55.6 percent with oral. Topical finasteride is not a zero-systemic-effect drug. It suppresses circulating DHT by roughly two thirds of what the tablet does. Systemic androgen effects are reduced, not abolished, and anyone choosing topical specifically to avoid sexual side effects should understand that they are lowering the exposure, not eliminating it.

There is no FDA-approved topical finasteride product in the United States. In April 2025 the FDA issued an alert about compounded topical finasteride, noting it had received 32 adverse event reports between 2019 and 2024, including erectile dysfunction, anxiety, suicidal ideation, brain fog, depression and decreased libido, alongside local irritation. Compounded products are not FDA approved, meaning their safety, effectiveness and quality have not been evaluated before marketing. In Europe the position differs: a finasteride cutaneous spray solution is nationally authorised in several member states including Germany, Italy and Portugal.

Ketoconazole, rosemary oil, saw palmetto

Ketoconazole shampoo has a better reputation than its evidence. A systematic review found seven studies in total, of which two were animal studies and five were human, covering 318 participants between them. The human studies reported increased hair shaft diameter and improvement on photographic assessment. The reviewers’ own conclusion was that ketoconazole is a promising adjunctive therapy and that randomised controlled trials are needed, which is the polite way of saying none exists. It is cheap, safe and plausible, and the entire case for it rests on surrogate measures in a few hundred people.

Rosemary oil rests on a single 2015 trial of 100 men, randomised 50 per arm, comparing rosemary oil against 2 percent minoxidil over six months. Four things about it are usually omitted. There was no placebo arm, so the fact that both groups improved from baseline at six months cannot be attributed to either treatment. The comparator was 2 percent minoxidil, the weaker concentration, not the 5 percent standard for men. Neither group showed any significant change at three months. And scalp itching was significantly more common in the rosemary group. “No different from minoxidil” in a two-arm trial of this size means the study failed to detect a difference, which is not the same as showing there is none. It has never been replicated.

Saw palmetto has five randomised trials and two cohorts behind it, at doses from 100 to 320 mg, with reported improvements including a 27 percent increase in total hair count and stabilisation in 52 percent of patients. It was well tolerated with no serious adverse events. The reviewers state that robust high-quality data are lacking and call specifically for trials examining the sole contribution of saw palmetto, which is the tell: it is nearly always studied inside multi-ingredient products, so its individual effect is unestablished.

Biotin and collagen

Biotin is in almost every hair supplement on the shelf, and it does nothing for hair in people who are not deficient in it.

A review of the literature found 18 reported cases in which biotin supplementation improved hair or nails, and in every one of them the patient had an underlying pathology causing the problem: biotin deficiency, biotinidase deficiency, brittle nail syndrome, or a similar condition. The conclusion was that there is a lack of sufficient evidence for supplementation in healthy individuals. A more recent systematic review of 10 human studies found that biotin monotherapy did not show consistent benefit on objective hair growth outcomes. The AAD’s guidance is that you should only take biotin, iron or zinc when a blood test shows a deficiency, and that supplementing normal levels can be harmful.

There is a specific hazard worth knowing. High-dose biotin interferes with laboratory immunoassays, and the FDA has continued to receive reports of biotin interference causing falsely low troponin results. Troponin is the blood test used to diagnose a heart attack. A man taking a high-dose hair supplement who arrives at an emergency department with chest pain can get a reassuring number that is wrong. Tell any clinician taking your blood that you take biotin, and stop it before planned testing.

Marine collagen has never been tested on its own for hair. The one controlled study available gave 83 subjects a product containing hydrolysed fish collagen alongside taurine, cysteine, methionine, iron and selenium, on top of drug treatment, and compared it against drug treatment with no tablet at all. There was no placebo. The outcome was a seven-point global assessment score rather than a hair count. It is not possible to attribute anything in that result to the collagen.

Exosomes and stem cells

This is the newest and most expensive category, and the regulatory position is unambiguous.

There are no FDA-approved exosome products. The agency’s position is that exosomes used to treat conditions in humans are regulated as drugs and biological products, which means they require premarket approval. That matters because it closes the loophole laser caps use: an exosome injection cannot be cleared as a device.

The FDA issued a public safety alert in 2019 after reports of serious adverse events in patients given products marketed as containing exosomes, stating that clinics offering them deceive patients with unsubstantiated claims and put them at risk. Its continuing position is that such products have not been reviewed or verified for quality, safety, purity or potency. The adjacent unapproved stem cell market has produced documented harm: the CDC investigated bacterial infections, including E. coli and Enterococcus faecalis, in patients given umbilical cord blood products that were recalled in 2018.

The clinical literature is thin. A systematic review of exosomes for hair regeneration found 11 clinical studies covering 298 participants, of which only two were randomised. Reported hair density increases ranged from 9.5 to 35 hairs per square centimetre, but risk of bias in the non-randomised studies was rated predominantly serious, owing to absent control groups and retrospective designs.

A clinic charging four figures for an exosome course is selling an unapproved biological product on the strength of two randomised trials. That is the whole picture.

This article is for information only and is not medical advice. Tell any clinician taking your blood that you take a biotin supplement. Talk to a qualified health professional about your own situation.