Coal tar hair dye ingredients are known to cause allergic reactions in some people, FDA's Lambert says. Synthetic organic chemicals, including hair dyes and other color additives, were originally manufactured from coal tar, but today manufacturers primarily use materials derived from petroleum. The use of the term "coal tar" continues because historically that language has been incorporated into the law and regulations.

The law does not require that coal tar hair dyes be approved by the FDA, as is required for other uses of color additives.

In addition, the law does not allow the FDA to take action against coal tar hair dyes that are shown to be harmful, if the product is labeled with the prescribed caution statement indicating that the product may cause irritation in certain individuals, that a patch test for skin sensitivity should be done, and that the product must not be used for dyeing the eyelashes or eyebrows.

The patch test involves putting a dab of hair dye behind the ear or inside the elbow, leaving it there for two days, and looking for itching, burning, redness, or other reactions.

"The problem is that people can become sensitized — that is, develop an allergy — to these ingredients," Lambert says.

"They may do the patch test once, and then use the product for 10 years" before having an allergic reaction. "But you're supposed to do the patch test every time," he says, even in salons.

And what about ending up with something other than the exact shade of strawberry blonde on the shelf? "Don't think the color on the box is the color you'll get," says Freier, the cosmetology instructor. "There are so many variables, like what chemicals are already in your hair and what your natural color is, that go into how your hair will turn out."

When using all hair chemicals, it's critical to keep them away from children to prevent ingestion and other accidents, and to follow product directions carefully. It sounds basic, but some people don't do it, says FDA's Halper. "If it says leave on hair for five minutes, seven minutes doesn't make it better," he says. "In fact, it could do damage."

Adapted from the January-February, 2001 issue of FDA Consumer.