Answer: Radium

By the start of the 20th century, we’d mostly gotten the trend of putting toxic things in makeup out of our system. Gone were the days of ladies powdering their faces with arsenic-based powders or smearing lead-based makeup on their cheeks. Still, the era of proper product testing and safety regulation was decades off, and there was still plenty of time left in the early 20th century to squeeze in some horrible choices.

The most notable of those choices was the inclusion, from around 1910 until the 1930s, of the radioactive substance radium, in everything from lipstick to eye shadow and every other makeup you can think of (as well as numerous other products, for that matter, like radium-infused butter and underwear). The products purported to help keep you young and protect your skin while, ironically, in reality they were damaging your cells and accelerating the deterioration of your body. People exposed to high levels of radium, like the famous “radium girls” who applied glowing radium paint on watch faces and military instrument panels, suffered from tumors, bone loss, and many died within years of the exposure.

Eventually, due largely in part to a very high profile lawsuit filed by five of the aforementioned “radium girls”, the public trust in radium shifted dramatically and in 1938, the Food, Drug, and Cosmetic Act outlawed the deceptive marketing practices that allowed companies to shamelessly tote the imagined health benefits of smearing radium-based makeup on your face or radium-infused butter on your toast.