A Health Crisis Rooted in Discrimination
In October 2022, the National Institutes of Health (NIH) published a landmark study in the Journal of the National Cancer Institute that drew a direct line between chemical hair straightening treatments and cancer risk. The study, drawing on data from the Sister Study — a prospective cohort of nearly 34,000 women — found that women who used chemical hair straighteners more than four times per year were approximately 2.5 times more likely to develop uterine cancer compared to non-users.
This finding is significant not only for public health but for the understanding of hair discrimination. Chemical straightening is not a neutral consumer choice. For millions of women with textured hair, it is a response to workplace grooming standards, social pressure, and institutional norms that penalise natural hair. The health costs of chemical straightening are, in a meaningful sense, costs imposed by discrimination.
What Chemical Straighteners Contain
Chemical hair straightening treatments work by breaking and reforming the disulfide bonds that maintain hair’s natural curl structure. The chemicals used to accomplish this bond restructuring include:
Formaldehyde and formaldehyde-releasing agents. Many “keratin treatments” and “Brazilian blowouts” contain formaldehyde or chemicals that release formaldehyde when heated. Formaldehyde is classified as a known human carcinogen by the International Agency for Research on Cancer (IARC). Exposure occurs through inhalation during salon application and through scalp absorption.
Lye-based relaxers (sodium hydroxide). Traditional relaxers use sodium hydroxide at high concentrations (pH 12–14) to break disulfide bonds. These products cause chemical burns to the scalp with improper application and permanently alter hair structure.
No-lye relaxers (calcium hydroxide with guanidine carbonate). Marketed as gentler alternatives, these products still operate at high pH levels and carry risks of scalp irritation and hair damage.
Cyclosiloxanes and parabens. Many straightening products contain endocrine-disrupting chemicals that may affect hormonal balance with repeated exposure.
Phthalates. Used as fragrance carriers and plasticisers in many hair products, phthalates are known endocrine disruptors with documented effects on reproductive health.
The NIH Study: Key Findings
The NIH Sister Study analysis, led by Dr. Alexandra White, produced several critical findings:
Dose-response relationship. The risk of uterine cancer increased with frequency of use. Women using straighteners more than four times per year had a hazard ratio of approximately 2.55 compared to non-users. Less frequent users also showed elevated risk, though the relationship was strongest at higher usage levels.
Racial disparity. While the chemical effect is not race-specific (the same chemicals affect all users), the study noted that Black women were disproportionately represented among frequent users — approximately 60% of participants who reported using straighteners were Black. This disparity is not biological but social: Black women use chemical straighteners at higher rates because of greater conformity pressure from workplace and social norms.
Mechanism. The researchers hypothesised that endocrine-disrupting chemicals in straightening products are absorbed through the scalp — which has higher absorption rates than other skin, especially when chemical burns or irritation are present — and affect the uterine tissue over time. The uterus is particularly sensitive to hormonal disruption.
Other health outcomes. While the headline finding concerned uterine cancer, the researchers noted associations between chemical straightener use and other hormone-sensitive conditions, though these findings require further investigation.
Beyond Cancer: Additional Health Risks
The NIH uterine cancer finding is the most serious but not the only health concern associated with chemical straightening:
Scalp damage. Chemical relaxers frequently cause scalp irritation, chemical burns, and permanent follicle damage. Studies report that 40–60% of relaxer users experience some degree of scalp irritation with each application.
Traction alopecia. Chemical processing weakens hair, making it more susceptible to breakage from tension. When combined with tight styling (weaves, braids, ponytails), chemically treated hair is at elevated risk for traction alopecia — a form of hair loss that can become permanent if follicles are irreversibly damaged.
Respiratory exposure. Salon workers who apply chemical straightening treatments face chronic inhalation exposure to formaldehyde and other volatile compounds. Occupational health studies have documented elevated rates of respiratory symptoms, eye irritation, and headaches among salon professionals who perform these treatments regularly.
Hair shaft damage. Chemical straightening permanently alters hair structure, reducing tensile strength, increasing porosity, and making hair more vulnerable to environmental damage. This structural damage cannot be reversed — it persists until the treated hair grows out.
The Discrimination Connection
The critical context for understanding these health risks is the discrimination that drives their use.
The Dove CROWN Coalition’s 2023 study found that 66% of Black women changed their hair for job interviews. Research on the psychology of hair conformity estimates that 80% of Black women have felt the need to change their natural hair for workplace acceptance. The economic cost of conformity — including spending on chemical treatments — is substantial.
When workplace grooming policies, hiring bias, and social norms create environments where natural textured hair is penalised, individuals are placed in an impossible position: accept professional and social consequences for wearing natural hair, or expose themselves to documented health risks by chemically altering it.
This is not an individual health decision. It is a structural health burden imposed by discriminatory systems. The NIH’s findings transform hair discrimination from a matter of dignity and economics into a matter of public health.
Regulatory Response
In the wake of the NIH study, regulatory attention has increased:
The US Food and Drug Administration (FDA) proposed banning formaldehyde in hair straightening products in 2023. The EU’s Cosmetics Regulation already restricts formaldehyde in cosmetic products but has not specifically addressed the formaldehyde-releasing agents common in straightening treatments.
However, regulation of chemical composition alone does not address the underlying problem: the discriminatory social structures that drive demand for straightening treatments. As long as natural textured hair is penalised in workplaces and schools, individuals will seek ways to alter their hair — and the market will provide products to meet that demand, with or without formaldehyde.
CROWN’s Position
CROWN’s approach to the health risks of chemical straightening operates on two levels:
Evidence. The CROWN Hair Commons captures chemical treatment history as a core data dimension. The CROWN Diagnostic’s NIR spectroscopy detects chemical residue — providing objective evidence of treatment history that can be correlated with CDI discrimination data. This evidence base will quantify the relationship between discrimination pressure and chemical treatment use at the European population level for the first time.
Root cause. By building the infrastructure to combat hair discrimination — through research, legislation, and cultural change — CROWN addresses the root cause that drives chemical straightener use. When natural hair is protected by law, accepted in workplaces and schools, and valued in culture, the pressure to chemically alter natural texture diminishes — and with it, the associated health risks.
The health risks of chemical straightening are not merely a hair care concern. They are a consequence of discrimination — measurable, documentable, and preventable. Preventing them requires the same infrastructure CROWN is building across all dimensions of its mission.