The influence of cosmetic treatments in the uptake of in vitro cocaine contamination in hair

Abstract Hair analysis is a powerful tool to assess drug use, yet the challenge of external contamination complicates its interpretation. Understanding the influence of cosmetic hair treatments is pivotal as their presence may affect this phenomenon. This study investigated the effects of four cosmetic treatments (bleach, henna, gel, and dry shampoo) on the external in vitro contamination of cocaine and its primary metabolite, benzoylecgonine (BE). Hair samples were divided into four groups: A‐hair treated with cosmetics then contaminated; B‐hair contaminated then subjected to cosmetic treatment; and C‐hair solely contaminated (control group). Negative hair samples ( n = 24) were immersed in a cocaine and BE aqueous solution of 1 μg/mL for 24 h. All hair samples were analyzed by a LC–MSMS procedure successfully validated according to ANSI/ASB Standard 036 guidelines (limit of quantification at 10 pg/mg). Henna in Group A ( n = 13) resulted in the most substantial reduction for cocaine (92%), while bleach in Group B ( n = 15) showed an 80% decrease. For BE, Group A henna ( n = 13) exhibited a 50% reduction, and Group B bleach ( n = 15) demonstrated a 71% decrease, all compared to Group C ( n = 24). The study found no significant differences concerning hair color (black ( n = 3), brown ( n = 10), red ( n = 5) and blond ( n = 6)) or shape (straight ( n = 6), wavy ( n = 16), curly ( n = 1), and coily ( n = 1)). All analysis were performed in triplicate with variations below 20%. These findings emphasize that cosmetic treatments do affect cocaine/BE concentrations in hair when exposed to external contamination, highlighting the importance of considering an individual's cosmetic history prior to interpretation.