Identifying Chemicals of Health Concern in Hair Extensions Using Suspect Screening and Nontargeted Analysis

Chemical exposures from hair extensions pose a growing public health concern due to their poorly characterized composition and limited regulatory oversight. Extensions are commonly made of human hair, other natural fibers, or synthetic fibers that may be treated with dyes, flame retardants, waterproofing agents, pesticides, antimicrobials, and conditioning agents with hazardous properties. Hair extension use may contribute to exposure and health disparities. We used nontargeted analysis (NTA) to understand the chemical composition of 44 hair samples. We performed suspect screening and NTA using two-dimensional gas chromatography-high-resolution mass spectrometry. We used the Highlight machine-learning platform to annotate detected chemical features by comparing their mass spectra to those of the National Institute of Standards and Technology library. We detected 933 chemical signatures, with 5,275 total detections across all samples. We confirmed and tentatively identified 169 chemicals then classified their potential hazard using structure (e.g., organohalogens) and presence on public chemical lists. Nearly 10% of samples contained hazardous organotin compounds, including some above 0.4% (w/w) tin. Four organotin structures were confirmed with reference standards, and seven structures were solved de novo. The remaining structures are tentatively annotated but unambiguously contain tin or tin and halogens based on the unique isotope patterns and mass defects. Forty-eight chemicals confirmed and tentatively identified in hair extensions were on a hazard list including California's Proposition 65. To our knowledge, this is the most comprehensive testing of hair extensions publicly reported. Follow-up research to understand exposures and policies to increase disclosure and reduce hazards will reduce health risks.