Researchers at Yale University have found that long term users of hair coloring products have an increased risk of developing non-Hodgkin's lymphoma (NHL), a cancer that attacks part of the body's immune system. "An increased risk of NHL was found only among women who began using hair-coloring products before 1980," said principal investigator Tongzhang Zheng, associate professor of environmental health at Yale School of Medicine. "Women who used darker permanent hair coloring products for more than 25 years showed the highest increased risk. We also found that the risk of NHL associated with hair coloring product use appears to vary based on subtype of the disease."
There has been a worldwide increase in NHL cases and little is known about the origin and the risk factors responsible for the increasing incidence of the disease. Zheng said previous studies on hair dye use and NHL have been contradictory and inconclusive. This is the first study to examine the impact of hair dye use with time period of use as a key factor.
"Hair coloring products have undergone tremendous change over the last 20 years," said Zheng. "Since 1980, many carcinogens have been removed from some formulas, which vary depending on whether the dye is permanent, semi-permanent, darker or lighter."
The six-year study was was published in the American Journal of Epidemiology.
Zheng and his colleagues did not find an increased risk of NHL overall among women who started using hair-coloring products in 1980 or later. The researchers suggest this may be due to changes in hair dye formulas over the past two decades or indicate that recent users are still in their latent period.
