Narrator: This is Science Today. Contrary to previous studies, researchers at the University of California, San Francisco found no association between hair dye and Non-Hodgkin's lymphoma. Elizabeth Holly, a professor of epidemiology, led the study, which included over four thousand participants, most of whom were women.

Holly: We looked at all different kinds of hair dye use. We looked at the temporary colors or hair darkeners, we looked at semi-permanent colors, we looked at permanent dyes and we also looked at exclusive use of each of these products because we wanted to know if it was one type of a product more than another that might be related to the incidence of lymphoma.

Narrator: Holly's study also dispelled a former theory that the dark hair dyes posed a greater risk of cancer.

Holly: This is a nice New Year's present for people - to be able to know that when they're dyeing their hair they don't have to worry about non-Hodgkin's lymphoma.

Narrator: Non-Hodgkin's lymphoma is the fifth leading cancer among both men and women - and its incident rate is increasing every year. For Science Today, I'm Larissa Branin.