Researcher Mimi C. Yu.

Even after adjusting for cigarette smoking (a known risk factor in bladder cancer), women who use permanent dyes at least once a month for one year or longer have twice the risk of bladder cancer as non-users, according to the study in an upcoming February issue of the International Journal of Cancer (already published on line). Monthly or more frequent users of 15 or more years have three times that risk.

The increase in bladder cancer risk also was observed in people who are exposed to hair dyes at work, such as barbers and hairdressers.

The research team, part of the USC/Norris Comprehensive Cancer Center, conducted the epidemiological study with 1,514 bladder cancer patients in Los Angeles, comparing them to another 1,514 people who lived in the same neighborhoods. They interviewed participants about health, lifestyle habits and occupations.

“Our bladder cancer study is the first to examine personal hair-dye use with the three major categories of dyes – permanent, semi-permanent and temporary dyes,” said Manuela Gago-Dominguez, researcher in preventive medicine and lead author of the study.

Researchers said the association with increased cancer risk was found only with permanent dyes, not semi-permanent or temporary hair color, which rinses out and fades after a series of shampoos.

“Our study is the first to demonstrate a frequency- and duration-dependent association between personal use of permanent hair dyes and bladder cancer risk,” said Mimi C. Yu, professor of preventive medicine and one of the study’s authors. “Our novel observations are provocative and carry enormous public-health implications. One should bear in mind, however, that these findings require confirmation before such exposure can be regarded as causal factors in bladder-cancer development.”

Bladder cancer currently accounts for 6 percent of all new cancer cases in men and 2 percent of all new cancer cases in women.

The American Cancer Society estimates that 53,200 Americans were diagnosed with the cancer and 12,200 Americans died from it in 2000.

Besides cigarette smoking, researchers say that exposure to arylamines – a family of chemicals – is a known risk factor for the disease.

Arylamines in hair dye have been found to cause cancer in laboratory animals, according to previous studies, and small amounts of these substances are absorbed through the skin during normal use. The body later expels the chemicals through urine, passing through the bladder.

Around the world, millions of people use hair dyes. More than one in three women over age 18 and one in 10 men over age 40 throughout Europe, North America and Japan use some type of hair coloring, the researchers reported, and permanent dyes account for about three-quarters of the global use.

In the USC study, researchers looked not only at those who used dye on their own tresses, but also those who used it as part of their job. The team found that those in the study who had worked as hairdressers or barbers for 10 years or longer faced a risk of bladder cancer five times greater than the general population.

Overall, those who had ever worked as a hairdresser or barber for at least one year experienced a 50 percent greater risk of such cancer.

About 2 million people work as hairdressers and barbers in North America and Europe alone, the researchers said.