Now, a European consumer watchdog group is blasting federal government regulators for failing to warn consumers that long-term use of hair dyes may increase the risk of bladder cancer.
"The more frequently a woman dyes her hair, and the longer she claims she's been using hair dyes, the higher the risk," says Dr. Mimi Yu, UCLA study author.
According to the UCLA study, permanent hair dye contains aromatic amines, chemical compounds related to ammonia which bond the color to the hair. When hair is dyed, trace amounts of these agents sink into the scalp and enter the blood vessels.
Some researchers believe the darker the shade, the more the amines and the greater the risk that these chemicals could cause a problem. That's what's making headlines right now, but keep in mind that an earlier study by the American Cancer Society followed hundreds of thousands of people since 1982 looking for bladder cancer. And those reserachers decided that the dye theory is dead wrong.
"The American Cancer Society study prospectively looked at these 600,000 people and found no increase in death, in mortality, from bladder cancer due to the use of hair dyes," says Dr. David Rosenthal, former president of the American Cancer Society.
For what it's worth, the UCLA study showed no link between cancer and all-natural dyes like Henna.