Hair Loss: What the Evidence Shows

Hair loss is a biological process with a real clinical literature behind it. This page reports what the trials and meta-analyses actually found — including where the established treatments still outperform the regenerative ones.

Scope of This Review

This page covers androgenetic alopecia — pattern hair loss — which is where almost all of the evidence sits. Other causes of hair loss (alopecia areata, telogen effluvium, scarring alopecias) have different mechanisms, different prognoses and different evidence, and are distinguished rather than merged.

It also keeps two treatment categories strictly apart. Platelet-rich plasma (PRP) has nine randomised controlled trials and several meta-analyses behind it. Cell and exosome therapies have no randomised placebo-controlled trial at all. Evidence generated for one is never used to support the other.

What Kind of Hair Loss?

The single most useful thing before considering any treatment is knowing which condition you have, because the evidence does not transfer between them.

Androgenetic alopecia (pattern hair loss) is progressive, genetically driven miniaturisation of follicles in androgen-sensitive areas. It is by far the most common cause and the only one with a substantial treatment literature. Prevalence rises steeply with age: in a community survey in Maryborough, Australia, mid-frontal hair loss affected 57% of women and 73.5% of men aged 80 and over¹.

Alopecia areata is autoimmune, patchy and can remit spontaneously. Its treatment pathway is immunological and quite separate.

Telogen effluvium is diffuse shedding triggered by illness, surgery, childbirth, nutritional deficiency or medication. It is usually self-limiting and resolves when the trigger is addressed. No trial supports injecting anything into it.

Scarring (cicatricial) alopecias destroy the follicle and replace it with fibrous tissue. These require dermatological diagnosis and anti-inflammatory treatment, and no regenerative approach can recover a follicle that is gone.

If you do not know which you have, that is the first question for a dermatologist — not a treatment decision.

The Biology

The hair growth cycle

Every follicle cycles independently through three phases: anagen, the active growth phase lasting years; catagen, a brief regression phase of a few weeks; and telogen, a resting phase of a few months, after which the old hair sheds and a new anagen begins. At any moment most scalp hairs are in anagen, and shedding of a modest number of hairs daily is normal.

What goes wrong in pattern hair loss

Androgenetic alopecia is a process of follicular miniaturisation, not follicular disappearance — at least at first:

1. In genetically susceptible follicles, dihydrotestosterone binds androgen receptors in dermal papilla cells
2. Each successive cycle has a shorter anagen phase
3. Each cycle therefore produces a thinner, shorter, less pigmented hair
4. Thick terminal hairs become fine vellus hairs
5. In advanced stages, chronic inflammation and fibrosis can destroy the follicle permanently

This is the fact that governs every treatment decision on this page. A miniaturised follicle is alive and retains stem cells in its bulge region — it can potentially be stimulated. A follicle replaced by scar tissue cannot. That is why treatment works better earlier: it is a statement about follicular viability, not about the patient.

The dermal papilla

The dermal papilla is a cluster of specialised mesenchymal cells at the base of the follicle. It controls the timing of anagen entry, regulates growth factor signalling, mediates the follicle's response to androgens, and determines hair thickness and length. Its progressive dysfunction is the proximate cause of miniaturisation, and it is the target of most regenerative approaches.

PRP: What the Evidence Shows

Platelet-rich plasma is the regenerative treatment for hair loss with by far the most published evidence, and that evidence is reasonably good.

The randomised-trial synthesis

A systematic review and meta-analysis restricted to randomised controlled trials — 9 trials, 238 patients — found that PRP increased hair density at both 3 and 6 months, with statistically significant differences compared with placebo. Two of seven studies reported adverse reactions; no serious adverse reactions were found. The authors conclude PRP is an effective and safe treatment for increasing hair density in androgenetic alopecia⁶.

The effect sizes

An earlier meta-analysis of 6 studies and 177 patients quantified the effect:

Both significant. The same analysis also examined percentage change, and found no statistically significant difference — hair number 24.12% (95% CI −12.76 to 60.99, P = .20) and thickness 32.63% (95% CI −16.23 to 81.48, P = .19). Its authors add that the results "should be interpreted with caution as it consists of pooling many small studies"⁵.

That split is worth understanding rather than glossing: the absolute measures reach significance and the percentage measures do not. Hair density per cm ^[2]is the more reliable way to describe this treatment, which is why this page uses it.

The individual trials

A randomised, evaluator-blinded, placebo-controlled half-head study — each patient serving as their own control — treated one side of the scalp with PRP and the other with placebo, three sessions at 30-day intervals. Of 23 patients enrolled, 20 completed. Against baseline, the treated side gained a mean of 33.6 hairs in the target area and 45.9 hairs/cm ^[2]in total density, with microscopy showing increased epidermal thickness and more hair follicles two weeks after the last treatment. No side effects were noted, and patients were followed for two years².

A randomised, double-blind, half-head study in 25 patients with three treatments a month apart found, at six months against baseline: hair density 179.9 ± 62.7, terminal hair density 165.8 ± 56.8, anagen hairs 67.6 ± 13.1 and telogen hairs 32.4 ± 13.1. Its authors conclude PRP "showed a positive effect" and could be regarded as an adjuvant therapy for androgenetic alopecia³ — adjuvant being their word, and a fair description of where it sits. Clinical and histomorphometric evaluation of activated PRP in pattern hair loss reported comparable findings⁴.

In women

PRP has been studied specifically in female hair loss. A systematic review and meta-analysis of 21 studies and 628 participants, restricted to randomised trials, found PRP significantly enhanced hair density and thickness, with a significant reduction in the number of hairs removed on pull testing. Adverse effects were mild and transient, with no difference in pain or discomfort versus control (RR 1.01, 95% CI 0.87–1.18). The authors note that effects vary with dose, injection interval and ethnicity, and call for tailored protocols⁷.

This matters because female pattern hair loss typically involves diffuse miniaturisation with follicles preserved — the situation in which a follicle-stimulating approach has something to work with.

How PRP Compares With the Established Treatments

This is the part most discussions of PRP skip, and it changes the picture.

Approximately equivalent to finasteride and minoxidil

A network meta-analysis of the six most common non-surgical treatments — dutasteride 0.5 mg, finasteride 1 mg, low-level laser therapy, minoxidil 2%, minoxidil 5% and PRP — screened 78 studies and analysed 22. Its finding: PRP, finasteride 1 mg in men and women, minoxidil 5%, minoxidil 2% and dutasteride in men are approximately equivalent in mean change in hair count following treatment. Low-level laser therapy ranked as the superior treatment⁸.

That equivalence is a genuinely strong result for PRP and it deserves stating plainly: an injected autologous preparation performs comparably to the two drugs that have decades of regulatory approval behind them.

The same analysis is equally clear about certainty. The quality of evidence for PRP versus placebo was rated very low; minoxidil 2% versus 5% was rated high. Minoxidil 5% and 2% reported the most drug-related adverse events (n = 45 and n = 23 respectively)⁸.

Where PRP ranks against minoxidil directly

A Bayesian network meta-analysis of 27 trials and 1,110 patients compared 5% minoxidil, PRP and microneedling — alone and in combination — for change in total hair density at 24 weeks. Ranked by probability of inducing improvement:

5% minoxidil plus microneedling was significantly better than PRP monotherapy (MD = 16 hairs/cm ^[2]) and microneedling monotherapy (MD = 17 hairs/cm ^[2])⁹.

Two conclusions follow, and both are uncomfortable for a regenerative-medicine page. Minoxidil monotherapy outranks PRP monotherapy. And PRP combined with microneedling ranked last of the six — below either component on its own.

Finasteride, represented accurately

Finasteride is frequently described as carrying a meaningful risk of sexual side effects. A network meta-analysis and benefit-risk assessment of finasteride and dutasteride, undertaken specifically in light of post-marketing reports of persistent sexual dysfunction, found that the active interventions "were not significantly different from placebo in eliciting sexual dysfunction", and were not significantly different from each other in efficacy. The authors state that the analysis "reiterate[s] the efficacy and safety of 5α-reductase inhibitors for the treatment of AGA"¹⁰.

Individual patients do report side effects and those experiences are real; what the pooled randomised data do not show is a rate distinguishable from placebo.

For women, low-dose oral minoxidil combined with spironolactone has been studied in female pattern hair loss and is an option worth raising with a dermatologist¹¹.

What this means

PRP is a legitimate treatment with randomised evidence behind it, performing comparably to the drugs. It is not a replacement for them, and the best available ranking places minoxidil monotherapy above it. Anyone presenting PRP as superior to established therapy is ahead of the data.

Cell and Exosome Therapy: A Much Thinner Base

This section is deliberately separate, because the evidence is not comparable to PRP's and combining them would misrepresent both.

There is no randomised placebo-controlled trial of cell or exosome therapy for hair loss.

Cell therapy. A study of 40 patients — 20 with alopecia areata and 20 with androgenetic alopecia, all treatment-resistant cases — gave a single session of either autologous bone-marrow mononuclear cells or autologous follicular stem cells. At six months there was significant improvement confirmed by immunostaining and digital dermoscopy, with mean improvement across groups rated "very good" and no serious adverse events. There was no significant difference between the two methods in either type of alopecia, and there was no placebo or untreated control arm — so the improvement is a within-group change¹².

Exosomes — mechanism. Laboratory and animal work has shown that exosomes derived from dermal papilla spheroids, enriched in miR-218-5p, up-regulate β-catenin and drive follicles from telogen into anagen more effectively than dermal papilla cells or minoxidil in those models¹³. This is preclinical: it establishes a plausible mechanism, not a clinical effect.

Exosomes — first human data. A prospective, open-label study treated 16 men aged 36–45 with mild-to-moderate androgenetic alopecia using a topical exosome preparation applied after microneedling. At 12 months, mean hair density had increased by 35 ± 6.5 hairs/cm ^[2]from baselines of 75–95 hairs/cm ^[2]; 80% reported noticeable improvement and 87% reported satisfaction. Side effects were mild scalp tenderness and irritation, resolving within 48 hours¹⁴.

That is real human data and it is encouraging. It is also 16 patients, with no control group, combined with microneedling — an intervention that has its own effect on hair density⁹. It cannot be compared with the PRP evidence above, and should not be.

Making a Decision

Get the diagnosis first. Pattern hair loss, alopecia areata, telogen effluvium and scarring alopecia look different under trichoscopy and have entirely different answers. Blood work for iron, thyroid function and vitamin D is reasonable where diffuse shedding suggests a systemic trigger — correcting a documented deficiency is worthwhile, and supplementing in its absence is not.

Start with what is best established. Topical minoxidil and, for men, oral finasteride have the largest and most certain evidence base⁸ ¹⁰. If the goal is maximum density gain, the combination that ranked highest was 5% minoxidil with microneedling⁹.

PRP is a reasonable addition, not a replacement. Its randomised evidence is real⁵ ⁶ ⁷, its own trial authors describe it as adjuvant³, and it performs comparably to the drugs rather than better than them⁸.

Cell and exosome therapy are investigational. If they are offered to you, ask what randomised evidence exists for the specific preparation. Currently the answer is none.

Timing is about the follicle. Miniaturised follicles can be stimulated; scarred ones cannot. Trichoscopy can establish which you have.

Questions worth asking any provider: What is my diagnosis, and how was it made? What is the evidence for this specific treatment in this specific condition? How will density be measured, and against what baseline? What proportion of your patients see no change?

What Sterling-Certified Partner Clinics Offer

For transparency, separately from the evidence above: partner clinics provide PRP scalp treatment, scalp microneedling, trichoscopic assessment and diagnostic blood panels. Session structure, preparation method, pricing and adjunct services are commercial and clinical arrangements determined at the clinic. They are not findings from the literature and are not presented here as evidence of effect.

Any treatment plan is a matter for a qualified clinician who has examined your scalp and established a diagnosis.

Frequently Asked Questions

Does PRP actually work for hair loss?

For androgenetic alopecia, yes — with real limits. A meta-analysis of 9 randomised trials found significantly increased hair density versus placebo at 3 and 6 months⁶, and pooled hair count improved by 17.90 hairs/cm ^[2](95% CI 5.84–29.95)⁵. What it does not do is outperform minoxidil⁹.

Is PRP better than minoxidil or finasteride?

No. Network meta-analysis places PRP approximately equivalent to finasteride 1 mg and minoxidil 5% in mean hair-count change⁸, and a ranking analysis of 27 trials put minoxidil monotherapy above PRP monotherapy⁹.

Does PRP work for women?

Yes — this is one of the better-evidenced questions here. A meta-analysis of 21 randomised studies in 628 women found significant improvement in hair density and thickness, with adverse effects no different from control (RR 1.01, 95% CI 0.87–1.18)⁷.

Will PRP work if I am completely bald on top?

Unlikely. PRP acts on follicles that still exist in miniaturised form. Where scarring has replaced the follicle there is nothing to stimulate. Trichoscopy can distinguish the two.

What about exosomes — I have seen a lot about them?

The mechanism work is genuine and preclinical¹³. The human data currently amount to one open-label study of 16 men, with no control group and combined with microneedling¹⁴. That is a starting point, not an evidence base.

Is finasteride as risky as people say?

The pooled randomised data do not show a rate of sexual dysfunction distinguishable from placebo¹⁰. Individual reports exist and should be discussed with a prescriber, but the trial evidence does not support treating it as a common outcome.

How many PRP sessions, and how often?

Published trials used three sessions at roughly one-month intervals² ³. Maintenance intervals have not been established by trial evidence, and any schedule beyond the trial protocols is a clinical judgement rather than a research finding.

Can PRP be combined with minoxidil?

The combination has been studied. In the ranking analysis, 5% minoxidil plus PRP (SUCRA 64.7%) outperformed minoxidil alone (53.9%)⁹, so the combination appears additive. Notably, PRP plus microneedling ranked lowest of the six interventions assessed.