Researchers have been looking at a possible connection between hair dye and certain types of cancer for years, but while the World Health Organization's cancer research agency
has classified on-the-job exposure to hair dyes as a probable carcinogen, there is no warning about personal use because the evidence is inconclusive.
This latest study published in the BMJ medical journal looked at data from 117,200 female nurses at Brigham and Women's Hospital in Boston, which included details on their exposure to hair dye.
The women did not have cancer at the start of the study and were followed for 36 years.
The results showed no increased risk of most cancers or of dying from cancer in women who reported having ever used permanent hair dyes compared with those who said they had never used such dyes.
"The headline result is that overall there is no difference in the rate of cancer in general in women who have used hair dyes and those that have not," said Paul Pharoah, a professor of cancer epidemiology at the University of Cambridge, in the United Kingdom. He was not involved in the research.
Specifically, the study found the use of hair dye did not increase risk of cancers of the bladder, brain, colon, kidney, lung, blood and immune system, or most cancers of the skin or breast.
However, the use of permanent dyes was associated with a slightly increased risk of the basal cell carcinoma of the skin, and this risk was higher in women with naturally light hair, the study said.
In addition, an increased risk of ovarian cancer and three types of breast cancer -- estrogen receptor negative, progesterone receptor negative, and hormone receptor negative -- were also linked to use of permanent dyes, with risk rising according to the cumulative amount of dye women were exposed to.
An increased risk of Hodgkin lymphoma was also seen with use of permanent hair dye but only for women with naturally dark hair.
The authors said that darker shades of permanent hair dye could be associated with a higher concentration of ingredients.
The most aggressive hair dyes are the permanent types, and these account for approximately 80% of hair dyes used in the US and Europe, and an even greater proportion in Asia.
For the cancers where the study reported an increased risk, "the results are not compelling," Pharoah told the Science Media Centre.
"The reported associations are very weak and given the number of associations reported in this manuscript they are very likely to be chance findings," he said.
"Even if they were real findings the associations may not be cause-and-effect, and even if they were causal associations, the magnitude of the effects are so small that any risk would be trivial."
Hair dye is estimated to be used by 50% to 80% of women and 10% of men ages 40 and older in the United States and Europe, according to the study.
The authors said in a press release their findings should "offer some reassurance against concerns that personal use of permanent hair dyes might be associated with increased cancer risk or mortality."
The study was observational so it couldn't establish cause and effect.
The authors also highlighted some limitations, including a lack of racial diversity in the participants, which mainly included white US women with European ancestry. They added that other unmeasured factors, such as use of other products, may have affected the results.