Ingredients of Trichological Shampoos with Alleged Beneficial Effects on Hair—What Is Really Known About Their Efficacy? A Scoping Review of an Area with More Unknowns than Knowns

Numerous ingredients in trichological shampoos are advertised as “active against hair loss”; however, the body of evidence behind such claims seems very limited or, in many cases, nonexistent. The aim of this study was to compile an inventory of substances advertised by shampoo manufacturers as “active” against hair loss and systematically review available evidence from clinical trials that would corroborate such claims. We screened declared compositions of trichological shampoos for ingredients advertised as active against hair loss or promoting hair growth. The second step was a systematic review of clinical trials of these substances used topically in the treatment of hair loss. A query in PubMed, Scopus, and Web of Science followed PRISMA and PICO guidelines with the strength of evidence assessed according to GRADE guidelines. We identified 43 trichological shampoos in which 112 individual ingredients were advertised as “active”. Of these, 36 ingredients were indicated as “active” in at least two shampoos and were subject to further study. In the search for evidence, 103,639 articles were screened for relevant information. Ultimately, we identified 29 clinical trials that tested 16 of the 36 ingredients for efficacy against hair loss. Only four ingredients were tested individually: adenosine (four trials; highest strength of evidence: moderate), caffeine (four trials; moderate), placental protein (two trials; low), and melatonin (one trial; moderate). Another 12 ingredients of interest were only tested as parts of complex preparations: Achillea millefolium extract, arginine, biotin, hydrolyzed wheat protein, hydrolyzed soy protein, Panax ginseng, panthenol, piroctone olamine, Prunus amygdalus dulcis, Rosmarinus officinalis, Serenoa serrulata, and Urtica dioica. Such a study design made it impossible to attribute the observed effects to any specific ingredient. No clinical trials of efficacy could be found for the remaining 20 (55.6%) substances repeatedly cited as “active”. At the present stage, scientific evidence for efficacy against hair loss is available only for caffeine, adenosine, placental proteins, and melatonin, but the overall strength of evidence is low. Moreover, a substantial majority of topical ingredients promoted as “active against hair loss” were never actually tested in clinical trials to verify such claims. While unsubstantiated claims of supposed beneficial properties often refer to alleged scientific evidence, there are major gaps to be filled in the field of non-prescription treatments for hair loss.