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Published on January 07, 2020

closeup of woman getting hair highlights

Do Hair Dyes Cause Breast Cancer?

You may have already read or heard about a recent study linking permanent hair dye use in women to an increased risk of breast cancer. Many articles have highlighted this study, but it’s important to remember an important fact: it was single study.

The idea of hair dye causing cancer isn’t exactly new. Many scientists have pointed out that some of the chemicals found in hair dyes could be associated with cancer in mice. The research actually began a few decades ago. To complicate matters, other researchers found no links between hair dye and tumors in animal studies. Findings in cancer research conducted with animals doesn’t always correlate to similar findings in humans, and so far, research done with humans has at best shown a weak link between dye and cancer.

But the new study did show an association between hair dye and breast cancer. So in light of previous research saying there isn’t a link, and the media’s current response to this single study, I got a little upset as a primary care provider.

Not because it’s an invalid study, but because of the actual details in the results of the study, the impact on real-life women, and the media’s handling of the study.

Breast cancer is a terrible and often tragic disease. It’s likely that it has claimed the life of someone close to you, and its specter can be quite anxiety-provoking. More than one in eight women will be diagnosed in their lifetime, and this fact is stressful for many women. Having a family history of breast cancer makes it even scarier to think about.

So knowing breast cancer is so common, shouldn’t women be worried about using hair dye if it increases their risk of developing breast cancer by 9% as this study says? Probably not.

The problem with the media’s reporting is that the study looked at a group of participants that are not the average woman. The women enrolled in the study each had a sister who was diagnosed with cancer, already putting them in a much higher risk group than normal. They were followed for a period of eight years, tracking their use of hair dye and straightener products.

Now, medical statistics is a complicated topic. The type of risk reported in the headlines is “relative risk,” meaning that compared to non-users those women using permanent hair dye were 9% more likely to get breast cancer during the study. This isn’t controversial. The problem is, in reality, the “absolute risk” of a woman, with a sister with breast cancer, developing cancer caused by hair dye is actually much less than 0.01% according to the study. To put it another way, more than 10,000 women, who have a strong family history of breast cancer, would need to use hair dye to cause a single case of breast cancer, leaving the other 99.99% of women unaffected.

Not so scary, eh? Click-bait journalism is all too prevalent, and you probably aren’t going to click on a story about a 0.01% increased risk of cancer.

This large difference in relative and absolute risk happens when the risk of something happening is low. A similar comparison is imagining you have a 9% “relative risk” of a tiger mauling you at the zoo, compared to not going to the zoo. In reality, the risk of being mauled by the tiger is almost 0% whether you’re at the zoo or at home, and that 9% increase is practically meaningless.

Now, the study does have merit. It points out that African-American women in the study had a much larger risk than Caucasian women, making it (slightly) more relevant. And, the study does help us think about the importance of lowering the risk for a disease, like cancer, stroke or heart attack which can help lead to a longer, healthier life.

This is especially true if you have a family history of the disease. It also points out that for people who want to do “everything” in their power to lower their risk of developing cancer, not dyeing their hair with permanent dye would be appropriate, even if it is an incredibly small increased risk.

But there are much more impactful ways to lower your risk for breast cancer than giving up the hair dye, like stopping smoking, being more physically active, losing weight, limiting excessive alcohol intake, and when possible, breastfeeding.

The study highlights our society’s fascination with every little study on various environmental and lifestyle minutiae that may contribute to a specific disease, but in reality likely plays such a small role that partaking or avoiding them is trivial.

So, while it is always a good idea to try to lower cancer risk whenever possible, try not to be stressed out about whether or not your next stylist appointment will grow you a tumor.

By Mark List, MD, Avera Medical Group 69th & Cliff

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