Hair Smoothing Products Contain Harmful Substances for Health
Chemical hair straightening products, widely used by women and particularly by women of color, contain substances that are concerning for health. These products, whether they are relaxers or keratin treatments like Brazilian blowouts, are often associated with an increased risk of fertility issues, uterine fibroids, and certain hormone-related cancers, such as those of the breast, uterus, or ovaries.
Relaxers work by breaking the disulfide bonds in hair using hydroxides, while keratin treatments smooth hair by hydrolyzing keratin to form an impermeable film. Both types of products can contain dangerous chemical substances, either intentionally added or present as contaminants. Among these are formaldehyde, formaldehyde-releasing preservatives, volatile organic compounds, fragrance ingredients, heavy metals like lead, and endocrine disruptors such as phthalates, phenols, and parabens.
Keratin treatments often contain formaldehyde or preservatives that release it, even when labels indicate the absence of this substance. Studies have revealed that products labeled as formaldehyde-free still contained it, with concentrations reaching up to 11.5%. Relaxers, on the other hand, are often rich in endocrine disruptors and fragrance ingredients. Analyses also show that relaxers intended for children can contain high levels of substances that are regulated or banned in other regions of the world.
Exposure to these products is not limited to users. Hair salon professionals, often women of color of childbearing age, are particularly exposed. They inhale the fumes released during treatments, especially when heat is applied, and absorb the products through skin contact. Studies show that hairstylists have higher levels of phthalate metabolites and other chemicals in their urine after a day at work.
The use of these products is rooted in a complex social and historical context. Eurocentric beauty standards and hair discrimination have led many women, particularly Black women, to adopt straightening practices from childhood. These practices, often passed down through generations, respond to strong societal pressures.
Current research highlights the need to study chemical exposures related to these products more thoroughly. Traditional methods, such as label analysis or targeted testing, are insufficient to capture the full complexity of the chemical mixtures present. More modern approaches, such as exposomics, could help better understand the extent of environmental exposures for both consumers and professionals. Additionally, community-informed interventions are essential to reduce exposures and the resulting health disparities.
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About This Study
DOI: https://doi.org/10.1007/s40572-026-00544-8
Title: Chemicals of Concern in Chemical Hair Straightening Products: A Scoping Review
Journal: Current Environmental Health Reports
Publisher: Springer Science and Business Media LLC
Authors: Emily Weaver; Marissa Chan; Lariah Edwards; Ami R Zota