About 33 million women use hair dyes to temporarily or permanently change their hair color. Most dyes marketed for use by women are known as coal tar hair dyes because initially coal tar was the only commercially practical source of material needed to synthesize the colors used in them. Most coal tar hair dyes contain colors derived from petroleum rather than coal tar. Because a color chemically identical to the petroleum-derived color could be derived from coal tar, the Food and Drug Administration (FDA) classifies petroleum-derived colors as coal tar colors and regulates hair dyes containing them accordingly. Coal tar hair dyes whose labeling contains a prescribed statutory warning concerning possible skin irritation and blindness are exempt from Federal Food, Drug, and Cosmetic Act provisions concerning adulteration, but they are not exempt from misbranding provisions of the act.