Fads are almost never a good thing, but rarely are they ever truly harmful. We dump a few hundred bucks into Tamagotchis, Beanie Babies, or Rubik's Cubes, and then the craze is over and we put all that crap in a shoebox to confuse our future grandchildren. However, some fads have poisoned thousands, started wars, and enslaved entire nations, all for the sake of some dumbass thing people wanted to ride, wear, or eat.
France's Radium Craze Makes Paris Radioactive
In 1898, Marie and Pierre Curie discovered radium, which (as its name suggests) is an intensely radioactive element that will poison the nuclear titfarts out of any living thing that comes into prolonged contact with it. Radium would eventually become the basis for the development of radiotherapy as a cancer treatment, but back then, people didn't have any idea what it did. So, because it glowed in the dark and was discovered at a time when science was considered to be magic, people began putting radium in every goddamn thing they could think of (Marie Curie herself kept radioactive salts by her bedside, and Pierre carried a piece of it around in his jacket like a bone-jellying pocket watch).
Right next to his radium condoms for his other toxic bone-jelly.
And thus began a radioactive craze that hit Paris (and to a lesser extent, the rest of the world). For instance, radium became a trendy cure-all additive, because for some inexplicable reason people decided that it was an invigorating life tonic ("It HAS to do something! It glows!"). It found its way into everything from cough medicine to toothpaste, as well as topical ointments, chocolate bars, and anal suppositories intended to improve your sexual prowess (and while we cannot agree that it would improve your libido, we concede that shoving the blazing fury of an eternal atomic sun into your asshole would certainly do something to your underbelt region).
We're guess something like Taco Bell, but in reverse.
They even sold radium water, which is exactly what it sounds like -- radioactive vitamin water peddled with the most hilariously inaccurate slogan ever: "A cure for the living dead."
But Parisians were equally enamored with radium's DayGlo properties and used it to make luminescent paint for watch faces and instrument panels. It was even used in face creams, lipstick, and other types of makeup, because apparently having your face glow like the death angel at the end of Raiders of the Lost Ark was a look that people appreciated in the early 20th century.