Chemical Straightening as a Source of Analytical Variability in Hair Testing: A Dual‐Analyte Case Report

Hair analysis is increasingly used in forensic toxicology; however, result interpretation may be influenced by cosmetic hair treatments. Although the effects of bleaching, dyeing, and thermal straightening have already been evaluated, data on permanent chemical hair straightening are scarce, particularly under in vivo conditions. This case report evaluates the impact of an alkaline-based permanent hair straightening procedure on the determination of an endogenous compound, gamma-hydroxybutyrate (GHB), and an exogenous drug, alprazolam, in hair. Hair samples were collected from a 39-year-old woman before and 1 month after undergoing chemical hair straightening based on ammonium thioglycolate. Adjacent hair strands corresponding to identical temporal windows were analyzed. GHB was quantified in 0.5-cm hair segments using a validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) method, whereas alprazolam was analyzed in 2-cm segments using a validated LC-MS/MS method for drugs of abuse and psychoactive pharmaceuticals. All analyzed segments were positive for GHB in both samples. After the straightening procedure, endogenous GHB concentrations showed a pronounced increase compared with pretreatment levels, with fold changes ranging from approximately 6 to 43 in corresponding segments. In contrast, alprazolam concentrations in segments corresponding to the reported period of drug intake decreased by approximately 1.7- to 2-fold following chemical straightening. This case report demonstrates that permanent chemical hair straightening can produce marked and analyte-dependent effects on hair drug concentrations. These findings emphasize the importance of systematic documentation of cosmetic hair treatments and careful interpretation of hair analysis results in forensic casework, particularly when analyte concentrations are low.