4. Killed because of hats
Many people think that “mad as a hatter” refers to the mental and physical side effects hatmakers endured from using mercury in their craft. Though scholars dispute whether this is actually the origin of the phrase, many hatters did develop mercury poisoning.
In the 18th and 19th century, a lot of men’s felt hats were made using hare and rabbit fur. In order to make this fur stick together to form felt, hatters brushed it with mercury.
It was extremely toxic. Especially if you inhale it. It goes straight to your brain. Many hatters also developed cardiorespiratory problems, lost their teeth, and died at early ages.
The mercury only affected the hatters—not the men who wore the hats, who were protected by the hats’ lining. (Source: nationalgeographic.com)