What are chemical hair straighteners, and what chemicals do they contain?
Chemical hair straighteners — also called relaxers — are products used to permanently or semi-permanently alter the structure of hair, making it straight or less curly. These products tend to be used predominantly by Black or African American women, and use often starts early, including during childhood and adolescence. Commercially available products can contain carcinogens and endocrine-disrupting chemicals, including formaldehyde and formaldehyde releasers, cyclosiloxanes, and various plasticizers such as phthalates [1]. High concentrations of metabolites of phthalates and parabens have been detected in urine samples from women who use chemical hair relaxers, and use has been associated with earlier puberty, infertility, and uterine fibroids [2].
Is there a confirmed link between hair straighteners and breast cancer?
The evidence is suggestive but not definitive. Multiple large prospective studies have found associations between frequent straightener use and breast cancer risk, though results vary by study population and methodology. The NIH Sister Study (n=46,709) found that among all participants, personal straightener use was associated with breast cancer risk (HR = 1.18, 95% CI: 0.99–1.41), with higher risk associated with increased frequency of use (p for trend = 0.02) [3]. A separate analysis from the same cohort found that frequent use of straighteners and relaxers more than 4 times per year, compared with non-use, was associated with a higher incidence of breast cancer (HR = 1.31, 95% CI = 1.05 to 1.63) [4].
What does the research say about dose-response — does using straighteners more often increase risk more?
Yes, multiple studies suggest a dose-response relationship. A 2020 study published in the International Journal of Cancer found that women who used chemical hair straighteners more than six times a year had about a 30% higher risk of developing breast cancer [5]. The Sister Study data also showed that those who used straighteners every five to eight weeks had a 31% higher breast cancer risk compared to non-users [6].
What about adolescent use specifically?
Adolescent exposure appears to be of particular concern. In the Sister Study, frequent hair straightener use during adolescence was associated with an increased risk of premenopausal breast cancer (HR = 2.11, 95% CI: 1.26–3.55), but not postmenopausal breast cancer [7]. This finding suggests that timing of exposure during hormonal development may be a significant factor.
Does applying straighteners to others also carry risk?
There is some evidence that it does, which has implications for hairdressers and stylists. Non-professional application of straighteners to others was non-significantly associated with breast cancer risk (HR = 1.27, 95% CI: 0.99–1.62) in the Sister Study [3]. This finding points to potential risk through skin absorption and inhalation of fumes during the application process.
Are straighteners linked to other cancers beyond breast cancer?
Research increasingly points to broader cancer risks. Use of hair straighteners and chemical relaxers has been associated with increased incidence of breast, ovarian, and uterine cancers in prior studies [4]. More recently, a 2025 study published in the Journal of the National Cancer Institute found that during a median follow-up of 13.1 years, use of hair straighteners and chemical relaxers was associated with a higher incidence of thyroid cancer (HR = 1.71), non-Hodgkin lymphoma (HR = 1.62), and pancreatic cancer (HR = 2.66) [8].
How does formaldehyde in these products contribute to cancer risk?
Formaldehyde is a key concern. When a stylist heats chemical straightening solutions, formaldehyde in the products is released into the air as a gas. The International Agency for Research on Cancer (IARC) identifies formaldehyde as a human carcinogen based on leukemia and nasopharyngeal studies [6]. Hair relaxers also contain endocrine-disrupting chemicals that can be hormonally active and carcinogenic, and several large studies have supported associations between hair relaxer use and breast, uterine, and ovarian cancers [2].
A Focused Look at Black Women and Breast Cancer Risk
Why is hair straightener use especially relevant for Black women?
Black women use these products at substantially higher rates than other groups. Current straightener use varied considerably by race in the Sister Study, with 74.1% of Black women reporting any use compared to just 3.0% of non-Hispanic white women [3]. In the Black Women’s Health Study, 95% of women reported past or current use of hair relaxers [9]. This means that cumulative lifetime chemical exposure through straighteners is far greater in the Black community on average.
What does the research specifically show about breast cancer risk in Black women who use straighteners?
The evidence from multiple cohorts reveals an elevated and concerning pattern. The Black Women’s Health Study, which followed 59,000 self-identified African American women for over 25 years, found that Black women who used hair products containing lye at least seven times a year for 15 or more years had an approximately 30% increased risk of estrogen receptor-positive breast cancer compared with more infrequent users. The researchers described the elevated risk for the heaviest users — approximately 20% of study participants — as concerning [9]. A subsequent analysis of the same cohort published in Carcinogenesis found that for heavy use (15 or more years, at least 7 times per year) of hair relaxers, the multivariable hazard ratio for breast cancer overall was 1.13 (95% CI: 0.96–1.33), a modest but notable association, particularly for ER+ disease in women without a first-degree relative with breast cancer [7].
Are the products marketed to Black women more dangerous?
Research indicates they may be. Products used predominantly by Black women may contain more hormonally-active compounds [3]. A 2016 EWG study of personal care products marketed to Black women found that fewer than one-fourth of those products were “clean” or had fewer potentially hazardous ingredients, compared to products marketed to the general public [10].
Do results vary by the type of relaxer — lye vs. non-lye formulations?
Yes, and the findings are complex. In the Black Women’s Health Study, lye-based relaxers were associated with ER+ breast cancer risk among African American women, while in the Women’s Circle of Health Study, lye formulations were more associated with ER-negative disease. The lack of consistency between studies may be partly due to misclassification of product type, as many participants did not know which type they were using, and use of lye and non-lye products were not mutually exclusive [7].
How does breast cancer mortality compare between Black and white women?
While Black women have a 4% lower incidence rate of breast cancer than white women overall, they have a 40% higher breast cancer death rate, according to the American Cancer Society [11]. Black women are more likely than white women to develop highly aggressive breast cancers with higher mortality rates, though researchers do not fully understand why. Chemical exposure through hair care products has been proposed as one contributing factor [9].
Has any research found no link between hair relaxers and breast cancer in Black women?
Yes, and this is why the scientific picture remains complex. An earlier analysis of the Black Women’s Health Study, published in 2007, found no association: researchers followed 48,167 Black women and found no increases in breast cancer risk associated with any categories of duration of hair relaxer use, frequency of use, age at first use, number of burns, or type of relaxer used [12]. However, this earlier study had a shorter follow-up period and captured a different era of product formulations than more recent work, and subsequent research has found more nuanced associations particularly for heavy, long-term users.
What do regulatory agencies say?
The FDA has proposed a ban on the use of formaldehyde in hair-straightening and smoothing products [5]. The IARC classifies occupational exposure to hair straightener chemicals — as experienced by hairdressers — as probably carcinogenic to humans, though personal use at home remains harder to classify due to lower and more variable exposure levels [6].
What should I do if I use chemical hair straighteners?
Current evidence does not support a blanket recommendation to stop, but it does support greater caution — particularly for heavy, frequent, long-term users. The minimal association between hair relaxers and breast cancer risk for moderate users is generally reassuring, but the elevated risk for the heaviest users is concerning, and researchers have called for urgent action to address racial disparities in breast cancer [9]. If you have concerns about your risk, speaking with a healthcare provider — especially if you are a heavy user, began using these products in childhood or adolescence, or have a family history of breast cancer — is a reasonable and advisable step.
Bibliography
[1] Schedin, Traci, Isabel Scarinci, and Miriam Mutambudzi. “Use of Hair Straighteners and Chemical Relaxers and Incidence of Non-Reproductive Cancers.” JNCI: Journal of the National Cancer Institute, 2025. https://doi.org/10.1093/jnci/djaf280.
[2] Bertrand, Kimberly A., et al. “Hair Relaxer Use and Risk of Uterine Cancer in the Black Women’s Health Study.” Environmental Research 238 (2023). https://doi.org/10.1016/j.envres.2023.117113.
[3] Eberle, Claire E., Dale P. Sandler, Kyla W. Taylor, and Alexandra J. White. “Hair Dye and Chemical Straightener Use and Breast Cancer Risk in a Large US Population of Black and White Women.” International Journal of Cancer 147, no. 2 (2020): 383–391. https://doi.org/10.1002/ijc.32738.
[4] Schedin, Traci, Isabel Scarinci, and Miriam Mutambudzi. “Use of Hair Straighteners and Chemical Relaxers and Incidence of Non-Reproductive Cancers.” JNCI: Journal of the National Cancer Institute (published online September 30, 2025). https://academic.oup.com/jnci/advance-article-abstract/doi/10.1093/jnci/djaf280/8267970.
[5] Southern Cancer Center. “Hair Products & Your Cancer Risk.” August 6, 2024. https://www.southerncancercenter.com/hair-products-your-cancer-risk/.
[6] Cleveland Clinic. “Can Hair Dye Increase Cancer Risk?” October 25, 2023. https://health.clevelandclinic.org/hair-dye-and-breast-cancer-risk.
[7] Coogan, Patricia F., Lynn Rosenberg, Julie R. Palmer, Yvette C. Cozier, Yulanda M. Lenzy, and Kimberly A. Bertrand. “Hair Product Use and Breast Cancer Incidence in the Black Women’s Health Study.” Carcinogenesis 42, no. 7 (2021): 924–930. https://doi.org/10.1093/carcin/bgab041.
[8] Schedin, Traci, Isabel Scarinci, and Miriam Mutambudzi. “Use of Hair Straighteners and Chemical Relaxers and Incidence of Non-Reproductive Cancers.” JNCI: Journal of the National Cancer Institute (published online September 30, 2025). https://academic.oup.com/jnci/advance-article-abstract/doi/10.1093/jnci/djaf280/8267970.
[9] Bertrand, Kimberly A., et al. “25-Year Study of Black Women Links Frequent Use of Lye-Based Hair Relaxers to Higher Risk of Breast Cancer.” Reported via PBS NewsHour / The Conversation, July 14, 2021. https://www.pbs.org/newshour/health/25-year-long-study-of-black-women-links-frequent-use-of-lye-based-hair-relaxers-to-a-higher-risk-of-breast-cancer.
[10] Environmental Working Group. “Study Links Hair Dye and Chemical Straighteners to Breast Cancer, With Risk From Dye Highest for Black Women.” https://www.ewg.org/news-insights/news/study-links-hair-dye-and-chemical-straighteners-breast-cancer-risk-dye-highest.
[11] American Cancer Society. “Breast Cancer Facts & Figures 2024–2025.” https://www.cancer.org/content/dam/cancer-org/research/cancer-facts-and-statistics/breast-cancer-facts-and-figures/2024/breast-cancer-facts-and-figures-2024.pdf.
[12] Rosenberg, Lynn, Deborah A. Boggs, Lucile L. Adams-Campbell, and Julie R. Palmer. “Hair Relaxers Not Associated with Breast Cancer Risk: Evidence from the Black Women’s Health Study.” Cancer Epidemiology, Biomarkers & Prevention 16, no. 5 (2007): 1035–1037. https://doi.org/10.1158/1055-9965.EPI-07-0116.
