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."
Some Women at Higher Risk
The cancer-causing chemicals linked to hair dye are members of a class of chemicals known as aromatic amines. The human body is able to detoxify these compounds. But because of their genetic makeup, some people can't detoxify the compounds. Those people, Yu last year reported in the journal Carcinogenesis, are the ones most at risk from hair dyes.
Zheng, too, is looking for genetic factors that increase a hair-dye user's risk of non-Hodgkin's lymphoma.
But Yu warns that this doesn't mean hair dyes don't pose a general risk.
"I would be hesitant to put women into two baskets -- so many genes are involved," Yu says. "I would say our study suggests the risks are stronger [for women lacking working detox genes], but I wouldn't say women who think they are not deficient could just assume that they are not at risk."