There's a story making the rounds right now suggesting that the use of hair relaxers—products that are used more often by African American women than women of other ethnicities—might cause uterine fibroids—a painful condition experienced more often by African American women than women of other ethnicities.
Nobody really knows why African American women seem to be more prone to uterine fibroids, and, on the surface at least, this connection seems like it might make sense. Relaxers and other products contain hormones and chemicals that act like hormones. So, maybe, those things are getting absorbed into the body and leading to the growth of fibroids.
Trouble is: That's just speculation. And the evidence used to back it up is pretty flimsy. The study this story is based on looks at nothing but broad correlations: African American women have more fibroids and African American women use more of these hair care products. That's a problem, because broad correlations can be really, really misleading.
At The Urban Scientist blog, Danielle Lee (a scientist who has experience with both fibroids and hair relaxers) talks about why the "evidence" being presented in this case isn't even close to the same thing as "proof".
Parabens and phthalates can do some funky things. (I don’t trust these chemicals.) They are problematic and should be evaluated for safety, especially by the US Food and Drug Administration. Parabens can be an estrogen mimic – but only slightly it seems. But it’s everywhere – not just in Black hair care products like shampoos and perms. Parabens are preservatives in cosmetics and pharmaceuticals, so it’s in lotions, shaving gel, KY Jelly, makeup, even in food. Phthlates are what make plastics flexible, transparent, durable and strong. Exposure to these chemicals is coming from who-knows-how-many-sources: those dissolving plastic pill caplets, adhesives in bandages, toys, food packaging, even textiles, and paint.
My problem with this study is that it doesn’t eliminate all of these confounding and possibly conflicting variables. Again, what was the reason for hypothesizing hair care products for the disparity? It’s a leap – a huge leap and the data just doesn’t convince me. In my opinion, finding strong correlations of relaxer use among African-American women who happen to have fibroids is an artifact. Culturally, getting relaxers is a very typical hair-care regime among adult black women today. It’s a cultural phenomenon. So is being ashy and using lotion — which potentially has the same possible EDC risks as hair care products. These studies fall far short in making a connection between high occurrence of uterine fibroids and hair care rituals of Black women.
I see Lee pointing out a couple of problems here. One: A correlational study like this doesn't account for many, many other ways women might come into contact with the hypothetical causal agent. So it doesn't make much sense to tie causality to one, single source. Two: In a correlational study with this many variables, the connection you see might not mean what you think it means. The authors of this paper wonder whether hair care products might be causing fibroids. Okay. But it could be just that women who are more likely to have fibroids also, coincidentally, are part of a culture that uses a lot of these hair care products.
Correlational studies are important. They're a good first step in noticing patterns that can tell us something important about human health. But correlational studies can't be thought of as "proof" of anything. They're a way to notice a problem exists. But they aren't a good way of solving problems.
Unfortunately, correlational studies, like this one, make the news a lot. And, when they do, they're treated as though they represent scientific proof. That's a problem. Even if you don't have fibroids or use hair relaxers, you should read Danielle Lee's full post on this study. It'll give you a better idea about the sorts of questions you should be asking every time you see a scary science headline in the newspaper.