Chemicals of Concern in Chemical Hair Straightening Products: A Scoping Review

Chemical hair straighteners may contribute to adverse health outcomes, particularly among women of color, due to their higher use of these products. However, there is limited research on which chemical ingredients and contaminants may be the most putative agents. We conducted a scoping review to summarize the existing exposure assessment literature on chemicals of concern in two popular types of chemical hair straighteners (chemical relaxers and keratin treatments) and provide recommendations for future research.

Twenty-one studies and reports used one or more of the following methods to identify chemicals of concern: product testing, ingredient label analysis, biomonitoring, and air monitoring. Multiple chemicals were characterized in these products including formaldehyde, formaldehyde releasing preservatives (FRPs), volatile organic compounds, fragrance ingredients, metals, and endocrine-disrupting chemicals (EDCs) (e.g., phthalates, phenols, and parabens). Chemical composition varied by product type, with keratin treatments more frequently containing formaldehyde or FRPs and relaxers containing EDCs and fragrance ingredients. In addition to assessing potential exposures for consumers, several studies highlighted the potential for higher exposures in salon workers. Multiple chemicals of concern, including endocrine active and carcinogenic chemicals, were identified in these products, and composition varied by product type. Future research should use new approaches, such as exposomics, to understand the full extent of environmental exposures among consumers and salon workers. Community-informed interventions are also imperative for reducing chemical exposures of concern and related health outcomes.