“Mad As a Hatter” Has a Medical Background

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. However, the phrase “mad as a hatter” — used to describe someone who’s crazy or prone to unpredictable behavior — didn’t originate with Carroll. Instead, it’s linked to the hat-making industry and mercury poisoning. In the 18th and 19th centuries, industrial workers used a toxic substance called mercury nitrate as part of the process of turning the fur of small animals into felt for hats. Workplace safety standards were often lax, and prolonged exposure to mercury caused employees to develop a variety of physical and mental ailments, including tremors, speech problems, emotional instability, and hallucinations.