Use of Chemical Hair Straighteners and Menstrual Disturbances

Background: Use of chemical hair straighteners (“relaxers”) is associated with higher risks of hormonally mediated conditions. We hypothesized users of relaxers would have a higher prevalence of abnormal uterine bleeding (AUB) and dysmenorrhea. Materials and Methods: We analyzed baseline data from Pregnancy Study Online, an internet-based preconception cohort study of North American pregnancy planners. We included 14,366 participants aged 21–39 years who enrolled during 2014–2024 and reported on their typical menstrual cycle characteristics when not using hormones. We collected data on history of use, age at first use, frequency per year, duration of use, and number of burns. We defined AUB as cycle length <24 or >38 days, flow ≥ 7 days, irregular cycles, and/or heavy flow (>30 pads/tampons per menses). We defined dysmenorrhea as severe cramps requiring medication and bed rest. We used modified Poisson regression models to estimate prevalence ratios (PRs) and 95% confidence intervals (CIs) for the associations of relaxer use with AUB and dysmenorrhea, adjusted for potential confounders. Results: Overall, 2% of participants were current users and 10% were former users of relaxers. The frequencies of AUB and dysmenorrhea were 31% and 8%, respectively. PRs for current (versus never) relaxer use were 1.16 (95% CI: 1.00–1.33) for AUB and 1.30 (95% CI: 0.94–1.80) for dysmenorrhea. Participants who reported ever experiencing burns (versus never use) had a higher prevalence of dysmenorrhea (1–4 burns: PR = 1.42, 95% CI: 1.04–1.93; ≥5 burns: PR = 1.46, 95% CI: 1.00–2.13). Conclusion: Relaxer use was associated with a higher prevalence of menstrual disturbances.