This article was first published in The Montreal Gazette.
There’s been no shortage of press coverage about the link between baby powder and ovarian cancer. Johnson & Johnson has lost a string of lawsuits recently with the biggest ordering a payout of $4.7 billion. But the science isn’t so clear-cut, and a new study in the Journal of the American Medical Association has suggested that the risk, if it exists, is very small.
Debates about the safety of talc have been going on for over 40 years. Talc is a mineral commonly used in cosmetic products, like talcum powder. So when a 1971 report found talc particles within the tissue of ovarian and cervical cancers, people were understandably concerned.
Early studies from the 1980s did show a link between talc and ovarian cancer and a number of subsequent studies did the same. But more recent research from the Nurses’ Health Study, Women’s Health Initiative and the Sister Study was actually negative.
There are a few possible explanations for this discrepancy. Talc, when mined, is frequently contaminated with asbestos. In 1976, cosmetic manufacturers permanently removed all asbestos from their products. So one possibility is that earlier studies were seeing the cancer causing effects of asbestos, rather than talc, and the more recent studies showed no risk because products are now asbestos free.
Another possibility for the discrepancy is recall bias. The earlier positive studies were case-control studies. These types of studies identify women with ovarian and then ask them about prior talcum powder use. In effect, they work backward. The more recent negative studies were cohort studies. These types of studies record talcum powder use among women and then look to see if they subsequently develop ovarian cancer. In effect, they work forward.
The danger with backward looking studies is that people with a particular disease may end up scouring their memory looking for reasons why they got sick and then over-report a particular risk factor or exposure. The problem is made worse if they have a prior reason to believe something is dangerous.
For example the African American Cancer Epidemiology Study found an overall link between talc and ovarian cancer. For women interviewed after 2014, talcum powder nearly tripled the risk of ovarian cancer, but for women interviewed before 2014 there was no increased risk. The year 2014 is significant because it saw a large class action lawsuit against Johnson & Johnson. The press coverage may have skewed how women remembered their prior talcum powder use, especially if they were diagnosed with ovarian cancer.
Recall bias may explain why the retrospective backward-looking case control studies were positive and the prospective forward-looking cohort studies were negative. The problem with cohort studies is that they need a lot of patients to research rare events like ovarian cancer. Even the recent JAMA study, which analyzed data on a quarter of a million women, said that it did not have enough people in it to exclude a very small increase in risk.
But then again, why use talcum powder at all? The American Academy of Pediatrics actually recommends against it, not for any cancer link, but because it can be inhaled by babies and irritate lung tissue. The American College of Obstetrics and Gynecology is similarly unimpressed by the actual need for talcum powder for any gynecologic purpose. So even though talc likely does not significantly increase the risk ovarian cancer, we could just stop using it altogether.
For those who do want to keep using it, there is another solution. They can buy baby powder made from cornstarch, because while all talcum powders are baby powders, not all baby powders contain talc.
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