Industry Says Hair Dye Safe
In a letter to WebMD, the Cosmetic, Toiletry, and Fragrance Association points to a 2000 review of the scientific literature on hair dyes and cancer by Johns Hopkins researchers. That study found the evidence linking hair dyes to cancer to be inconclusive. It called for further research using improved methods.
The CTFA statement also points to two large epidemiologic studies that found no link between hair dyes and cancer.
"The safety of hair dyes is supported by the overwhelming wealth of scientific research, including several well-designed studies conducted by prestigious institutions such as the American Cancer Society and Harvard University," the CTFA notes. "These large epidemiology studies include more than 570,000 and 120,000 women respectively, and showed no elevated health risk for women using hair dyes."
"The hair color industry reaffirms its confidence in the safety of hair dyes."
Zheng and colleagues, however, note that two other large epidemiological studies reached different conclusions. They suggest that all of these studies were limited by methodological problems that may have underestimated exposure to hair dye.
Zheng says the cosmetic industry has been very helpful in providing information helpful to researchers.
Are Today's Products Safer?
Zheng's team found no increased non-Hodgkin's lymphoma risk in women who began coloring their hair after 1980. That raises a serious question. In 1979, the hair care industry drastically changed the formulation of most hair dyes to remove known cancer-causing agents.
Does that mean hair dyes made after 1980 are safe? Or is it just that not enough people have used the new products long enough to get cancer? Zheng says it's impossible to tell from his study.
The strongest evidence linking hair dyes to cancer comes from Mimi C. Yu, PhD, professor of preventive medicine at the University of Southern California's Keck School of Medicine. Yu's team showed that the more hair dye a person uses, the higher that person's risk of bladder cancer.
Yu says that scientists don't like to base recommendations on just a few studies.
"Is it time to alarm women? The evidence is starting to build up. The hair dye products as they exist out there may not be entirely safe," Yu tells WebMD. "Definitely more work needs to be done. But the evidence has built up to the point that the scientific community should take note. There should be more work done because we may have a not-so-safe consumer product out there."