High-throughput screening for cancer-relevant chemicals in hair relaxer products sold in Kenya

Introduction: Hair relaxer use is associated with increased risks of several hormone-related cancers, including uterine, ovarian, and breast cancer. Given the high prevalence of relaxer use among Black women and women of African ancestry, unequal exposure to toxicants in these products might contribute to observed disparities in cancer incidence and mortality. Although recent regulatory efforts have targeted specific chemicals such as formaldehyde and formaldehyde releasers, hair relaxers may contain additional unregulated chemicals and chemical mixtures of concern. Comprehensive data on the chemical composition of these products remain limited. Methods: As part of a larger investigation, we identified commonly used hair relaxers among women in two counties in Kenya (Embu and Nakuru) and purchased 19 products (11 cream relaxers and 8 multi-component relaxer kits) from local retailers and beauty shops between May and July 2024. Non-targeted two-dimensional gas chromatography-high-resolution mass spectrometry (GCxGC-HRMS) was used to identify and semi-quantify semi-volatile compounds in sample extracts. Inductively coupled plasma-mass spectrometry (ICP-MS) and atomic absorption spectroscopy were employed to screen for heavy metals and mercury, respectively. The Highlight™ machine learning system and a search of the National Institute of Standards and Technology library facilitated data processing and suspect screening. Tentatively identified chemicals were cross-referenced with authoritative hazard databases, including the European Union's Cosmetics Regulation (EC) No 1223/2009 lists of prohibited (Annex II) and restricted (Annex III) chemicals, which align with the Kenya Bureau of Standards cosmetic regulations. Results: We detected 353 individual features across all samples and identified 83 chemicals with medium-to-high identity confidence, including multiple known or suspected carcinogens. Over 50% of samples contained at least one chemical appearing on an established hazard list. Notably, lead and radioactive uranium-both banned in EU cosmetics-were detected in nearly 10% of the samples. Conclusions: This study provides the first high-throughput chemical characterization of commercially available hair relaxers commonly used by Black women and women of African ancestry in Kenya. The detection of numerous carcinogenic and restricted substances highlights an urgent need for strengthened regulatory oversight, policy action, and evidence-based interventions to reduce exposure to hazardous chemicals in hair and personal care products, emphasizing the importance of evidence-based policies and interventions to eliminate hazardous exposures and advance equitable cancer prevention globally.