The decision to classify talc as “probably carcinogenic to humans" was based on "limited evidence" talc could cause ovarian cancer in humans, "sufficient evidence" it was linked to cancer in rats and "strong mechanistic evidence" that it shows carcinogenic signs in human cells, the WHO’s International Agency for Research on Cancer (IARC) said on Friday, July 5, 2024.

Occupational exposure

Talc is a naturally occurring mineral which is mined in many parts of the world and is often used to make talcum baby powder. Most people are exposed to talc in the form of baby powder or cosmetics, according to the Lyon-based IARC. But the most significant human exposure to talc occurs when th mineral is being mined, processed or used to make products, it added.

The agency said there were numerous studies which consistently showed an increase in the rate of ovarian cancer in women who use talc on their genitals. But it could not rule out that the talc in some studies was contaminated with cancer-causing asbestos.

"A causal role for talc could not be fully established," according the agency’s findings published in The Lancet Oncology.

Kevin McConway, a statistician at the UK’s Open University not involved the research, warned that for the IARC’s evaluation, the "most obvious interpretation is actually misleading". The agency is only aiming "to answer the question of whether the substance has the potential to cause cancer, under some conditions that IARC do not specify," he said to AFP.

Because the studies were observational and so could not prove causation, "there isn’t a smoking gun that the talc use causes any increased cancer risk," he added.

Johnson & Johnson’s settlement

The announcement comes just weeks after US pharmaceutical and cosmetics giant Johnson & Johnson agreed to pay $700 million to settle allegations it misled customers about the safety of its talcum-based powder products.

Johnson & Johnson did not admit wrongdoing in its settlement, even though it withdrew the product from the North American market in 2020.

In the 1970s, concern arose about the contamination of talc with asbestos, often close in nature to the ores used to make talc. Then studies pointed to a higher risk of ovarian cancer among talcum powder users.

A summary of studies published in 2020 covering 250,000 women in the United States did not find a statistical link between the use of talc on the genitals and the risk of ovarian cancer.

Acrylonitrile

Also on Friday, the IARC classified acrylonitrile, a chemical compound used to make polymers, as "carcinogenic to humans", its highest warning level. It cited "sufficient evidence" linking acrylonitrile to lung cancer.

The polymers made with acrylonitrile are used in everything from fibres in clothes to carpets, plastics and other consumer products. It can also be found in cigarette smoke and air pollution.