Are Today's Products Safer? continued...
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."
Cancer-Causing Chemicals in Hair Dye
Perhaps the evidence of most concern comes from the FDA's National Center for Toxicological Research. In a study reported last September in Chemical Research in Toxicology, FDA researcher Robert J. Turesky and colleagues looked for a known carcinogen -- called 4-ABP -- in hair dye products bought off the shelf at U.S. supermarkets and hair salons.
"4-ABP was detected in eight of the 11 hair dyes and found in black, red, and blonde hair dyes but not in brown hair dyes," Turesky and colleagues reported.
Yu notes that none of the off-the-shelf products contained 4-ABP as a regular ingredient. Instead, she says, the products were contaminated with the substance -- probably as a byproduct of the chemical process through which dyes are made.
"We have found the smoking gun," Yu says. "This team of FDA scientists actually have detected a known human carcinogen in samples of products on the shelf being sold every day to consumers."
The good news, Yu says, is that since 4-ABP is not a necessary ingredient of hair dye, manufacturers can take action.
"If it is a contaminant, we can make the product safer," Yu says. "A woman whose mental health is pegged on not having gray hair showing, she doesn't have to choose between so-called 'looking old' and piling cancer risk on herself. Because if that hair dye can be made safer, it should be."
Zheng isn't so optimistic. He says he doesn't think chemicals found in hair dyes are directly responsible for cancer. He suggests that permanent hair dyes -- particularly the darker colors -- cause harmful chemical reactions.
"The major issue is not whether the products' current contents may or may not cause cancer," Zheng says. "The issue is that permanent hair dyes all use an oxidizing process that will create new chemicals that are not in the original dye. The oxidizing process will create compounds that will cause cancer. The concern isn't over the compounds in the products, it is the oxidizing process of permanent hair dyes."