The origin of the phrase, it's believed, is that hatters really did go mad. The chemicals used in hat-making included mercurous nitrate, used in curing felt. Prolonged exposure to the mercury vapors caused
What caused hatters to go mad?
In medieval Europe , mercury was used in medicine and manufacturing. Later, hatmakers commonly cured felt using a form of mercury called mercurous nitrate. As the hatmakers inhaled mercury vapors over time, many experienced neurological symptoms of mercury poisoning. By 1837, “mad as a hatter” was a common saying.
Where did Mad hatters originate?
Lewis Carroll's 1865 novel “Alice's Adventures in Wonderland” famously features an eccentric character called the Hatter, who's referred to in the story as “mad” and became popularly known as the Mad Hatter.
