With changes in the 1980s, even safer now?
The study of hair dyes and cancer has “major public health implications” because the use of hair dye is widespread, Dr. Zhang and colleagues write in their article. They estimate that 50% to 80% of women and 10% of men aged 40 years and older in the United States and Europe use hair dye.
Permanent hair dyes “pose the greatest potential concern,” they stated, adding that these account for approximately 80% of hair dyes used in the United States and Europe and an even higher percentage in Asia.
The International Agency for Research on Cancer classifies occupational exposure to hair dyes as probably carcinogenic, but the carcinogenicity resulting from personal use of hair dyes is not classifiable – thus, there is no warning about at-home usage.
Notably, there was “a huge and very important” change in hair dye ingredients in the 1980s after the Food and Drug Administration warned about some chemicals in permanent hair dyes and the cosmetic industry altered their formulas, lead author Dr. Zhang said.
However, the researchers could not analyze use before and after the changes because not enough women reported first use of permanent hair dye after 1980 (only 1890 of 117,200 participants).
“We could expect that the current ingredients should make it safer,” Dr. Zhang said.
The researchers report that ever-users of permanent hair dyes had no significant increases in risk for solid cancers (n = 20,805; hazard ratio, 0.98, 95% confidence interval, 0.96-1.01) or hematopoietic cancers overall (n = 1,807; HR, 1.00; 95% CI, 0.91-1.10) compared with nonusers.
Additionally, ever-users did not have an increased risk for most specific cancers or cancer-related death (n = 4,860; HR, 0.96; 95% CI, 0.91-1.02).
As noted above, there were some exceptions.
Basal cell carcinoma risk was slightly increased for ever-users (n = 22,560; HR, 1.05; 95% CI, 1.02-1.08). Cumulative dose (a calculation of duration and frequency) was positively associated with risk for ER– breast cancer, PR– breast cancer, ER–/PR– breast cancer, and ovarian cancer, with risk rising in accordance with the total amount of dye.
Notably, at a cumulative dose of ≥200 uses, there was a 20% increase in the relative risk for ER- breast cancer (n = 1521; HR, 1.20; 95% CI, 1.02-1.41; P value for trend, .03). At the same cumulative dose, there was a 28% increase in the relative risk for ER-/PR- breast cancer (n = 1287; HR, 1.28, 95% CI, 1.08-1.52; P value for trend, .006).
In addition, an increased risk for Hodgkin lymphoma was observed, but only for women with naturally dark hair (the calculation was based on 70 women, 24 of whom had dark hair).
In a press statement, senior author Eva Schernhammer, PhD, of Harvard and the Medical University of Vienna, said the results “justify further prospective validation.”
She also explained that there are many variables to consider in this research, including different populations and countries, different susceptibility genotypes, different exposure settings (personal use vs. occupational exposure), and different colors of the permanent hair dyes used (dark dyes vs. light dyes).
Geographic location is a particularly important variable, suggested the study authors.
They pointed out that Europe, but not the United States, banned some individual hair dye ingredients that were considered carcinogenic during both the 1980s and 2000s. One country has even tighter oversight: “The most restrictive regulation of hair dyes exists in Japan, where cosmetic products are considered equivalent to drugs.”
The study was funded by the Centers for Disease Control and Prevention and the National Institute for Occupational Safety and Health. The study authors and Dr. White have disclosed no relevant financial relationships.
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