Several studies, including a widely reported-on study published recently in the International Journal of Cancer, have examined the link between hair dye and cancer. But the media members who cover these studies do not always gleam the truth from naked rows of numbers and confidence intervals. For reporters and especially laymen readers, a wider perspective can provide more insight.

Mike McRae filed this report in Science Alert.

A new study reported this week claims that of the thousands of ingredients that go into hair products used to dye and straighten our hair, some might play a role in kick-starting breast cancer in women already at risk. But before you panic and throw out your box dye, there are a few things we need to explain here.


We need to look behind the results and include some other numbers. All of these percentages reflect relative, not absolute risk. As we have explained before when reporting on association studies:

“Relative risk means how much more likely one group is to develop a disease in comparison to another (..) Meanwhile, absolute risk is the one that tells you how likely you are to get a disease at all.”

That absolute risk is usually a really, really small number. In this case, none of the women in the study had a prior diagnosis of breast cancer. But since the people in the database all had a family member with breast cancer, their risk of developing the disease was already above that of the general population.