In 1783 an article was published in the London Magazine about a tree in Indonesia that could kill everything within 15 miles leaving the Earth bare and dotted with the skeletons. In fact, the Upas tree really exists and it does contain a powerful toxin, but this story was blown way out of proportion.
In the 1700s Johann Cohausen wrote a paper on the prolongation of life with the help of an elixir produced in part from the breath of young women accumulated in bottles. Later he owned up that the work had been just a satire.
About 30 years ago a leaflet with a list of a number of food additives as carcinogens was circulated in Europe. It caused a huge mass panic in many countries, especially France, but eventually was exposed as a false.
Discovered in 1912, the Piltdown man, was supposed to be the fossilized remains of a humanoid. About 50 years later that people discovered the elaborate hoax and determined that the skull was actually of a human male while the jawbone was of an orangutan.
Written by Horace Miner in the mid 90s, the focus of this paper was on a little known North American tribe that was obsessed with oral cleanliness. Despite of this seemed to be true, it actually turned out to be a satire. Nacirema spelled backwards is “American" and the ritual, which was described, was just brushing teeth.