Hair Straightening Products Are Associated with Increased Uterine Cancer Risk
Based on the first and only epidemiologic study examining this relationship, frequent use of hair straightening products (more than 4 times per year) is associated with a 2.5-fold increased risk of uterine cancer, while hair perming products show no significant association. 1
Evidence from the Sister Study
The Sister Study, a large prospective cohort of 33,947 women aged 35-74 years followed for an average of 10.9 years, provides the strongest evidence on this topic:
- Ever use of straightening products was associated with an 80% increased risk of uterine cancer (HR = 1.80,95% CI = 1.12 to 2.88) 1
- Frequent use (>4 times in the past 12 months) showed an even stronger association with a 2.55-fold increased risk (HR = 2.55,95% CI = 1.46 to 4.45) 1
- Hair dyes and permanents/body waves showed no association with uterine cancer risk 1
Biological Plausibility
Hair straightening products may contain hazardous chemicals with endocrine-disrupting and carcinogenic properties that can be absorbed systemically through the scalp 1. This is particularly concerning for uterine cancer, which is predominantly hormone-sensitive (>70% are type I endometrial cancers) 2.
Clinical Implications by Product Type
Straightening/Relaxer Products
- Avoid frequent use (limit to ≤4 applications per year if use is necessary) 1
- Consider alternative hair styling methods that do not involve chemical straightening 1
- Women using these products frequently should be counseled about the potential increased risk 1
Perming/Body Wave Products
- No increased risk demonstrated in the available evidence 1
- These products appear safe from a uterine cancer risk perspective based on current data 1
Hair Dyes
- No association with uterine cancer risk identified 1
- Can be used without concern for uterine cancer risk specifically 1
Important Caveats
This is the first epidemiologic study to examine the relationship between hair straightening products and uterine cancer, so replication in other populations is needed 1. However, the study's prospective design, large sample size, racially diverse cohort, and dose-response relationship (stronger association with more frequent use) provide robust evidence 1.
The specific chemicals driving this association have not yet been identified, warranting further research 1. Women should be informed that while the relative risk increase is substantial (2.5-fold for frequent use), uterine cancer remains relatively uncommon in the general population, with approximately 27 cases per 100,000 women annually 3.
Screening Recommendations
Women who frequently use hair straightening products should be counseled to report any abnormal vaginal bleeding promptly, as this is the primary symptom of uterine cancer 3. This includes bleeding between periods, after sex, or any unexpected bleeding after menopause 3.