An analysis of nearly four decades' worth of research on health and hair dyes suggests that today's coloring agents pose only a nominal, if any, risk of cancer.
Hair dye risks have been long linked to a family of chemicals called aromatic amines, which are carcinogenic. But a team of Spanish and Canadian scientists, which pooled results from 80 studies, found that certain cancer-causing compounds are no longer used, lowering health risks.
"In the 1970s, dye makers were using more toxic chemicals, such as 2,4-diaminotoluene and 2,4-diaminoanisole, which are no longer used," said Mahyar Etminan, an epidemiologist at Royal Victoria Hospital in Quebec, whose work helped deem the dyes safer than previously believed.
"Hair dye is something a lot of people are using, and if dye caused cancer, this would be a significant public health concern," Etminan said.
While his findings offer a degree of reassurance, he acknowledged that additional research is needed.
In today's Journal of the American Medical Association, Etminan and Dr. Bahi Takkouche of the University of Santiago de Compostela in Spain reported that in North America and Europe, about 33 percent of women and 10 percent of men use hair dyes.
Hair coloring agents have been linked to breast, skin and bladder cancers, leukemia and lymphoma.
Skeptics to the new risk-free message abound. Among them is Dr. Tongzhang Zheng of Yale University, who last year conducted one of the largest studies on cancer risk and hair dyes.
"Studies like these," Zheng said of Etminan's research, "prove nothing."
He called the analysis deeply flawed. Because the research was observational and did not involve patients, Zheng said, Etminan and colleagues could not gauge patients' susceptibility to dyes or the amount of dye any individual used.
Zheng had found that long-term use of dark-colored permanent dyes doubles a person's risk of certain cancers, particularly lymphoma. The new research did not specify dye types or colors. Zheng's study was one of 80 examined by Etminan's team.
"When we analyzed all of the studies, we found a slight increase in cancers of the blood," Etminan said. "But that risk was not very high."
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