According to background information in the article, "there is growing concern worldwide about a possible increase in the risk of cancer among users of hair dyes." The authors add, "An association between hair dyes and cancer would be an important public health concern since about one-third of women in Europe and North America, along with 10 percent of men older than 40 years, use some type of hair dye. Permanent dyes, the most aggressive type, represent 70 percent of the market share even more in Asia."
Bahi Takkouche, M.D., Ph.D., from the University of Santiago de Compostela, Spain, and colleagues analyzed data found in a medical literature search identifying 79 studies from 11 countries to examine the association between personal use of hair dyes and relative risk of cancer.
"Our results indicate that, globally, there is no effect of personal hair dye use on the risk of breast and bladder cancer," the authors report. "There is a borderline effect for hematopoietic cancers (for example, leukemia and multiple myeloma). However, the evidence of a causal effect is too weak to represent a major public health concern."
"Some aspects related to hematopoietic cancer and other cancers that have shown evidence of increased risk in one or two studies should be investigated further," the authors write in conclusion. "Efforts should be targeted toward the assessment of the risk of cancer in occupational settings where exposure to hair dyes is more prolonged and has a higher concentration and frequency than personal exposure."