…women who used permanent hair dyes at least once a month experienced a 2.1-fold risk of bladder cancer relative to non-users… We estimate that 19% of bladder cancers in women in Los Angeles County, California, may be attributed to permanent hair-dye use. (Gago-Dominguez et al. 2001)
The use of hair color products appears to increase the risk of non-Hodgkin’s lymphona… If these results represent a causal association, use of hair coloring products would account for 35% of non-Hodgkin’s lymphoma cases in exposed women and 20% in all women. (Zahm et al. 1992)
Many dye products contain ingredients called “coal tar dyes” that are specifically exempt from federal authority over adulterated products that can harm health. These include dyes made by Clairol, Revlon, L’Oreal, and others. Coal tar hair dyes are one of the few products for which FDA has issued consumer advice on the benefits of reducing use, in this case as a way to potentially “reduce the risk of cancer” (FDA 1993).
Coal tars and coal tar pitches are known human carcinogens (IARC 1987). The specific components of coal tar used in hair dyes — aromatic amines — have been shown to mutate DNA (IARC 1993), and to cause cancer in animals (Sontag 1981). An increasing number of studies of humans link long-time hair dye use with cancer, including bladder cancer, non-Hodgkin’s lymphoma, and multiple myeloma. Ingredients that fall under FDA’s definition of “coal tar dyes” can now be derived from either petroleum or coal tar, but studies have not been done to determine if these differences in manufacturing influence the dyes’ potency with respect to cancer.
Much of the evidence linking hair dyes with bladder cancer comes from studies of hairdressers. In seven of 10 populations studied (from the US, Norway, Sweden, Finland, Denmark, Japan), scientists found elevated incidence of bladder cancer among hairdressers, barbers, beauticians and cosmetologists exposed to hair dyes — 40 percent higher, on average, than population-wide risks. Hair dye exposure was also linked to bladder cancer in seven of 12 case-control studies focused specifically on occupational history among bladder cancer victims (Gago-Dominguez et al. 2001).
In 1993 the International Agency for Research on Cancer found that “occupation as a hairdresser or barber entails exposures that are probably carcinogenic” (IARC 1993), and a recent study by scientists from the University of Southern California’s School of Medicine shows that hairdressers and barbers with more than 10 years on the job face a five-fold increase in bladder cancer risk compared to people not exposed to hair dye (Gago-Dominguez et al. 2001).
Is cancer a risk outside the beauty industry, for consumers who dye their hair? In 1982 the National Bladder Cancer Study failed to find a relationship between hair dye use and bladder cancer risk among 3,000 bladder cancer victims. While this study has provided some assurance of low risks from hair dye exposure among people outside the beauty industry, a growing number of more sensitive, focused studies are heightening concerns that long-time or frequent hair dye use does, in fact, substantially increase cancer risks. These findings have been catalyzed by more sophisticated research techniques that include the collection of detailed information on the type of hair dye used, and the inclusion of factors that account for an individual’s genetic susceptibility to cancer.
In 2001 researchers from the University of Southern California’s (USC) School of Medicine found that women using permanent hair dye at least once a month more than double their risk of bladder cancer (Gago-Dominguez et al. 2001). Earlier studies had failed to segregate the use of permanent dye from semi-permanent and temporary dyes; the USC study showed this may be a critical distinction. The authors estimate that “19% of bladder cancers in women in Los Angeles County, California, may be attributed to permanent hair-dye use” (Gago-Dominguez et al. 2001). This study is to date the largest and most scientifically rigorous on permanent hair dye and bladder cancer incidence.
USC researchers also found that women who are genetically vulerable to bladder cancer (so-called “slow acetylators” who are exposed to some carcinogens for longer periods of time) more than quadruple their risk of bladder cancer with long-time or frequent use of permanent hair dye (Gago-Dominguez et al. 2001). These associations see further confirmation in a study performed by researchers at Dartmouth Medical School that also found links between permanent hair dye use and bladder cancer (Andrew et al. 2004).
New studies have identified the particular chemicals in hair dye thought to be linked to bladder cancer as aromatic amines, chemicals derived from coal tar but best known as potent bladder carcinogens in cigarette smoke (Yu et al. 2002). Association of permanent hair dyes with non-Hodgkin’s lymphoma, mutiple myeloma, colorectal adenocarcinoma, lung and upper aerodigestive tract cancers has been studied but associations have been both positive and negative, or only preliminarily studied (Czene et al. 2003; Skov and Lynge 1994; Zahm et al. 1992; Brown et al. 1992; Grodstein et al. 1994; Herrinton et al. 1994; Holly et al. 1998; Robinson and Walker 1999). Among the stronger findings from these studies are those from the National Cancer Institute, where researchers found that 20 percent of all cases of non-Hodgkin’s lymphoma may be linked to hair dye use (Zahm et al. 1992).
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