Talc

Talc is a very soft mineral made of magnesium, silicon, and oxygen (Mg3Si4O10(OH)2); it is at the very end of the In fact, it is the softest mineral known, although the alkali metals in their pure forms and some other substances like wax are softer. It is often sold powdered as talcum powder, combined with corn starch as a part of baby powder. Since talc and asbestos are commonly formed near each other in nature, there are concerns about asbestos contamination in baby powder, where spreading it in the genitalia (in order to keep underwear dry) can lead to ovarian cancer. These concerns have been dated as far back as the 1960s, though regulations have been addressed, and talcum powder in the market should be asbestos-free.

The (IARC) classifies talcum powder containing asbestos as carcinogenic, while asbestos-free talcum powder is not classified; however, when applied to genitalia, it is classified "possibly carcinogenic", based on the very limited evidence.

Despite the asbestos-free products, there have been fears that the talcum powder itself, since it is formed similarly to asbestos, can also cause cancer. Manufacturers of baby powder, Johnson & Johnson's in particular, have faced 17,000 lawsuits involving allegations that the baby powder, contaminated or not, leads to ovarian cancer. Scientific evidence for talcum powder causing ovarian cancer, however, is very weak, especially when considering that ovarian cancer is rare to begin with. Most research relies on the limited case-control study framework, though more recent cohort studies (which are more effective at observing potential cause-and-effect relationships) found no evidence of a link. A study in 2014 found no link. One of the largest cohort studies to date (thus reducing recall bias), published in January 2020, found no relationship between baby powder use and ovarian cancer in a sample size of 252,745 women.

Christopher Booker, a one-of-a-kind crank, believed that talcum powder and asbestos are the same compound lumped as "asbestos". He used this line of thought not to argue that talcum causes cancer, but that asbestos is harmless. No other well-known cranks have really tried arguing that they're the same, mind you.