Contradicting longstanding research, Harvard scientists have determined that hair dye does not cause cancer.

Scientists at the Medical School and the School of Public Health surveyed 99,000 women over 19 years and found no link between hair dye and cancer. Their results were published last Wednesday in the Journal of the American Cancer Institute.

"It is a very good study and has to be taken quite seriously," said Dr. Noel S. Welss, professor of epidemiology at the University of Washington in Seattle.

The common belief that hair dye caused cancer was based on a finding in 1975 by Dr. Bruce G. Ames, director of environmental health at the University of California at Berkeley. Ames observed that hair dye caused mutations in bacteria.

The results prompted companies to replace the mutagens in their hair dye products with safer alternative chemicals, Ames said.

"We know hair dye seeps through the scalp into the blood, which could cause blood cancers--leukemia or lymphomass," said Dr. Francine Grodstein, co-author of the study and a teaching fellow in epidemiology at the School of Public Health.

But according to Harvard epidemiologists, the presence of mutagens in hair dye doesn't necessarily prove the dye is significant in causing cancer.

Leona D. Samson, professor of toxicology at the School of Public Health, said "valid numbers" attributing cancer to a particular substance could only be obtained by studying sufficiently large populations.

"The epidemiologists can compare this [cancer] risk with, say, the risk of smoking," Ames said.

The Harvard study used data derived from a larger ongoing survey of 120,000 nurses from 11 states who answer questions every two years. Of the nurses who used hair dye from 1976 until 1982, none showed an increased risk for cancer.

The study only considered interviews conducted before the subjects developed cancer because victims tend to distort the reasons for their illness when they fall sick.

"A sick person who smoked one cigarette 10 years ago may say they are a smoker, whereas a healthy person will skip the question," Grodstein said.

Bleached blondes may take comfort in the study, but for those dying their hair black, the scientific results are less encouraging. A separate study published in February by the American Cancer Society found a 6 percent increase in cancer in those who had used black dye for a long period of time.