Hair dyes linked to cancer

Healthfacts, August, 1992

First, the press kit arrives from the hair products industry, containing letters from "top scientists" at major medical centers. Each offers a detailed critique of a new study showing that hair dyes are associated with an increased risk of non-Hodgkin's lymphoma, a cancer of the lymph tissues. The study's findings were characterized in the industry's press release as "incorrect and needlessly alarmist."

The study that so alarmed the hair dye manufacturers arrived several days later in the July issue of the American Journal of Public Health. Shelia Hoar Zahm, Sc.D., and colleagues at the National Cancer Institute questioned 426 people with blood cancers (leukemias and lymphomas) about their use of hair dyes, and compared their responses with those of 1,432 people of similar ages who do not have cancer. The people with cancer had been diagnosed between 1983 and 1986.

All participants were asked about their use of permanent hair dyes, semipermanent dyes that wash out after several shampoos, and products that gradually color the hair. Where deaths had occurred, a relative was questioned about the hair dye usage of the deceased.

Dr. Zahm and her colleagues found that the rate of nonHodgkin's lymphoma was 50% higher among hair dye users, as compared to nonusers. (Nonusers have a 1% rate and users have a 1.5% rate of this type of cancer.) The rate is even higher (a two- to fourfold increase) in those who had used permanent hair dyes, particularly the dark colors--black, brown, brunette, and red.

Not a Definitive Study

In a telephone interview, Dr. Zahm was asked about the industry criticisms leveled at her study. "This is not a definitive study, by any means, but it is consistent with some reports in the medical literature already. It's biologically plausible, given what we know about the compounds in dyes," she replied, referring to animal studies conducted decades ago, which showed that coal tar-based hair dyes contain components that cause cancer.

The experts chosen by the hair products industry to review the new study raised numerous questions, specifically about its conclusion and the validity of the participants' recall regarding hair dye usage.

"It comes down to the public's right to know," said Dr. Zahm. "Do you wait until something is absolutely nailed down? Or do you let people know there's a moderate increased risk? The tobacco industry is still waiting for the definitive study about smoking and lung cancer."

Asked why the study was confined to people who had the relatively uncommon blood cancers, Dr. Zahm explained that this was part of a much larger study of people exposed to agriculture-related substances in the Midwest. "We asked the questions relating to all known risk factors for these cancers," she said. "We added the hair dye questions because of a 1988 study, which found an association between lymphoma and hair-coloring product use in men."

Dr. Zahm laughed when asked whether she had ever experienced such intense industry criticism of her other research efforts. "Oh sure, I published a study in 1986 showing a link between the herbicide 2,4-D [dichlorophenoxyacetic acid] and non-Hodgkin's lymphoma. This is a common weed killer people use on lawns as well as in agriculture," she explained.

"The industry group, called the 2,4-D Industry Task Force, operated in a similar way to the hair products industry," said Dr. Zahm, referring to the press kit filled with refutations sent to media around the country. "Several studies since mine have supported the finding," she said. "So it stood the test of time ."

FDA's Reaction

One may wonder how the FDA, charged with protecting the public from unsafe products, will react to Dr. Zahm's hair dye study. In a telephone interview, the FDA's John Bailey, Ph.D., explained that experts at his agency believe it was a well-conducted study. "But our scientists say the connection [between hair dyes and cancer] is not strong enough for us to issue a recommendation that consumers should abandon the use of hair dyes."

Warning Obscured

The coal tar-based hair dyes constitute the majority of hair dyes on the market, according to the FDA. A list of the coal tar dye's active ingredients must be included with the product, said Dr. Bailey, who is the acting director of the FDA's division of colors and cosmetics. But they are identified by their various chemical names, such as pphenylenediamiene. A consumer would have to be a chemist to pick out the coal tar dyes.

Dr. Bailey offered an easier method. "There's a reverse way to ascertain pretty conclusively whether or not you are dealing with a coal tar hair dye," he said, advising consumers to look for this caution statement:

"This product contains ingredients which may cause skin irritation in certain individuals. A preliminary test according to company directions should first be made. This product should not be used for dyeing the eyelashes or the eyebrows. To do so might cause blindness."

What would it take to produce more definitive action from the FDA regarding the safety of coal tar dyes? "In order to resolve this, we need more research that goes after the issue directly," replied Dr. Bailey. "The inclusion of questions regarding hair dye use in this [Dr. Zahm's] study was an add-on. [Her findings] raise an eyebrow, but they are not sufficient for a regulatory action."