BACKGROUND The number of articles evaluating the efficacy of platelet-rich plasma (PRP) in androgenetic alopecia (AGA) and alopecia areata (AA) has increased exponentially during the last years. This systematic review and meta-analysis is aimed at evaluating the benefit of PRP in the treatment of alopecia. MATERIAL AND METHODS We searched MEDLINE (through PUBMED), Embase, and CENTRAL for relevant data. Treatment
effect was described by mean difference (MD) and risk difference with 95% confidence intervals (CI). The GRADE system was used to assess the certainty of the body of evidence. RESULTS We found 27 controlled trials (1,117 subjects) that met our inclusion criteria: 18 trials (713 subjects) in patients with AGA, and 9 (404 subjects) in patients with AA. Eleven studies had a split head design. There was heterogeneity in types of PRP (e.g., activated and non-activated) and administration schedules. PRP was compared to saline injections (18 studies), local steroid injections (4 studies) and other comparators (5 studies). Most commonly reported outcomes were hair density and hair regrowth. It was not possible to pool all outcome data because of heterogeneity in reporting, and because reporting was often limited to a single study. Compared to saline injections, PRP injections increased hair density over a medium-term follow-up (MD, 25.6 hairs/cm(2); 95 % CI: 2.62-48.57), but the evidence was rated as low quality due to inconsistency and risk of bias. In individuals with AA, it is unclear whether PRP injection compared with triamcinolone injection increase the rate of subjects with hair regrowth (very-low quality of evidence due to inconsistency, imprecision, and risk of bias). There were no serious adverse events related to PRP injection or control treatments. CONCLUSIONS There is limited evidence showing benefit of PRP for treatment of alopecia, and most of this evidence is of low quality.