Jan. 26, 2004 -- Long-term use of permanent hair dye -- in dark colors -- doubles a person's risk of certain blood cancers, new research shows.
Earlier studies have linked permanent hair dyes to bladder cancer as well as to the group of diseases known as non-Hodgkin's lymphoma. Non-Hodgkin's lymphoma rates are up all over the world. Nobody knows why, says Yale researcher Tongzhang Zheng, ScD.
Zheng suspected that hair dyes might play a role. Use of hair dye is increasing. And the products -- especially the permanent types in dark colors -- may expose users to dangerous chemicals. So Zheng led a research team that analyzed hair dye use in 601 women with non-Hodgkin's lymphoma and in 717 similar women without cancer.
The results: An increased risk of non-Hodgkin's lymphoma was observed for women who reported the use of hair coloring products before 1980. Women who used dark-colored permanent hair-coloring products for more than 25 years doubled their risk of non-Hodgkin's lymphoma. The risk was nearly the same for women who used more than 200 applications of these products. No increased risk was seen in women who used semi-permanent dyes or temporary rinses.
So should women stop using permanent hair dyes?
"Hair coloring is a personal decision for all kinds of reasons," Zheng tells WebMD. "But if I am the person, if semi-permanent or temporary dyes could serve my issue, I would do it. Because these contain much less of the ingredients linked to cancer."
Zheng's report appears in the Jan. 15 issue of the American Journal of Epidemiology.
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."
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."