mythbuster graphic The incidence of certain cancers has increased sharply over the past 50 years, and the quest to find out the reason for this disturbing trend been a long and complicated one. No one knows yet what causes most cancers, although some risk factors have been identified. You may have heard about a possible link between hair dye and certain kinds of cancer. Studies on the association between hair dyes and cancer have generated mixed results.

Some studies examining the claim that hair dyes increase the risk of certain types of cancer have found a link. In the 1970s, researchers at the National Cancer Institute discovered that rats fed large doses of hair dye ingredients (including substances found in coal tars, which are used for dark-colored dyes) were more likely to develop cancer than rats left unexposed to these substances. The FDA responded by requiring a warning label to be placed on dyes containing certain substances, and many manufacturers stopped using these ingredients. However, some scientists fear that replacement compounds may have similar chemical structures and cause comparable reactions in the body.

The American Journal of Epidemiology recently published a study suggesting that people who frequently used permanent, dark-colored hair dyes before 1980 (which is when the ingredients changed and coal tar was removed) were at a slightly elevated risk for developing non-Hodgkin’s lymphoma, a relatively common cancer of the lymph nodes. Although the removal of certain coal tar ingredients may have reduced the risk of cancer, it still may be too early to determine the long term health effects of this product change.