"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 epidemiology and 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 Connecticut is one of those areas with a confirmed increase. 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 conducted on 601 Connecticut women diagnosed with varying subtypes of NHL between the ages of 21 and 84. The women were asked to identify the type of hair coloring products they had ever used, length of time used, and their age when they stopped using it. The study included a control group of 717 women.
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.