The active ingredient in most dandruff shampoos, coal tar has been a known to cause cancer since the 18th century in industrial workers. But although the hazards of industrial coal are well-established, the dangers of pharmaceutical coal tar are under dispute. Makers of dandruff shampoos found the levels of carcinogens were below the risk level set forth in Proposition 65, meaning they would not have to label their product. Proving that pharmaceutical coal tar is a danger is the major obstacle in the case, and Gottesfeld told the San Fransisco Bay Guardian that he worries a ruling in favor of the companies would undermine the very foundation of Proposition 65.
"When a company is forced to label the product or make the product safer, nine times out of ten it opts to make the product safer," says Gottesfeld. As a result of Proposition 65, Preparation H no longer contains mercury, and calcium supplements no longer contain lead.