Effect of cosmetic hair treatment and natural hair colour on hair testosterone concentrations

Purpose Testosterone analysis in hair allows for retrospective evaluation of endogenous testosterone concentrations, but studies devoted to investigating confounders in hair testosterone analysis have hitherto been scarce. The current study examined the stability of testosterone concentrations between two hair samples collected three months apart and investigated two potential confounding factors: natural hair colour and cosmetic hair treatments. Methods Testosterone was analysed with an in-house radioimmunoassay with a limit of detection adequate for the purpose. Results The testosterone concentrations from the two samplings, at baseline and three months later, had an intra-individual correlation of moderate strength (rho = 0.378, p<0.001, n = 146). Hair treatment, such as colouring or bleaching, seemed to increase testosterone concentrations (p = 0.051, n = 191, and in a paired analysis in a subset of the cohort p = 0.005, n = 24), while no effect of natural colour in untreated hair (p = 0.133) could be detected. Conclusion The current results suggest that cosmetic hair treatments need to be considered in hair testosterone analyses and demonstrate the utility of a radioimmunoassay to reliably measure testosterone concentrations in small hair samples in women.