Looking through my drafts and found this—no idea why I hadn’t published it, as it seemed to be pretty much done. Maybe I did publish it and Tumblr hiccuped? Anyway, here it is.
I researched this, because I dye my hair all the time. The dye itself is semi-permanent color, but I have to bleach first in order for it to take well. This shade of pink doesn’t happen by itself. :P
Basically, the risk associated with maternal hair-dying, if it exists, is not for pregnancy loss but for an elevated risk of certain childhood cancers. Since the 1980s, numerous studies have been done; some of them found a correlation and many did not (and keep in mind that studies that do not find a correlation are less likely to be published, and therefore are probably underrepresented).
The most recent study I can find, “Maternal Hair Dye Use and Risk of Neuroblastoma in Offspring,” published in the journal Cancer Causes & Control in 2005, found a correlation between maternal hair dying and the most common of childhood cancers, neuroblastoma. Specifically, they found that a child with neuroblastoma was about 1.6x as likely to have a mother who had dyed her hair during pregnancy or in the month preceding it.
Personally, I don’t find it terribly convincing, because their response rates were low and like most studies of substance use effects in pregnancy, it’s entirely dependent on retrospective accounts. Such accounts are heavily biased toward finding an effect, because people whose children developed some kind of problem are likely to have racked their brains about what they might have done during pregnancy that could possibly have caused it, whereas people whose children did not develop a problem are likely to have gotten much fuzzier about what they did or didn’t do. Reports on frequency especially are likely to be suspect.
Another odd aspect of this study is that they found a greater effect for temporary hair dye than for permanent dye, despite the fact that permanent dye is typically made up of nastier chemicals—this might be explained by more frequent exposure or less use of professional assistance/ventilation for temporary dye use.
This study acknowledges another study from 2002 that found no association between maternal hair-dying and childhood cancer (“West Coast study of childhood brain tumours and maternal use of hair-colouring products” published in the journal Paediatric and perinatal epidemiology). Response rates for this study, as well as sample sizes (around 600-800 cases in the case group and the control group), were almost identical to the 2005 study that did find an effect.
As noted, studies of this type in particular and published studies in general are biased toward finding an effect. Given the fact that the literature overall is actually, if anything, skewed towards the “no effect” side, I personally did not change my hair-dying behavior. [Note: In fact, I had just had it redyed like three weeks or so before AJ was born… those hospital linens got stained pretty pink.] It’s all about your own evaluation of the risks involved.
One thing you can do to minimize risk if you do want to dye your hair is to book appointments for the first available slot of the day, so that you don’t get exposed to any chemicals other than your own—the one thing that definitely IS bad for pregnant people is hanging out in a chemical-saturated environment on a regular basis, which is why working in a salon dying lots of people’s hair is definitely NOT recommended.