Mad as a Hatter

Also: Mad as a March hare

Meaning of Idiom ‘As Mad as a Hatter’

To be as mad as a hatter means to be completely insane or demented. 1 Kirkpatrick, Elizabeth M. The Wordsworth Dictionary of Idioms. Ware: Wordsworth, 1995.,2Ammer, Christine. American Heritage Dictionary of Idioms. Boston: Houghton Mifflin Harcourt, 2013.

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Examples of Use

“We never went near Mr. Blackwell’s house. He’s mad as a hatter.”

“My boss is as mad as a hatter. He told us all that he’d fire us if we didn’t buy him a birthday present.”

Mad Hatter illustration from Alice in Wonderland
The Mad Hatter from Alice in Wonderland He was “as mad as a hatter” because he was a hatter!


Contrary to popular belief, this idiom did not actually derive from Lewis Carrol’s character in Alice’s Adventures in Wonderland, the Mad Hatter. The expression existed long before, during the early 1800s, whereas Carrol’s book was written in 1865. The expression and the character were references to the fact that hatmakers who made felt hats used mercurous nitrate to stabilize the felt and thus suffered from mercury poisoning, which caused what was called erethism or erethism mercurialis, commonly known as mad hatter disease. This mercury poisoning affected the entire nervous system and caused tremors, irritability, shyness, depression, low self-confidence, and timidity. Sometimes, symptoms could progress to complete delirium when exposure was prolonged. The Mad Hatter in Alice in Wonderland certainly displayed some of these characteristics but it is not known how much Carroll actually drew from the medical condition. It is often claimed that Theophilus Carter, an eccentric British furniture maker, was the inspiration for the character.

March Hare and Mad Hatter in Tea Party scene, Through the Looking Glass
The March Hare and Mad Hatter in the tea party scence in Through the Looking Glass They were both pretty mad. Here they are putting dormouse’s head in a teapot.

The variant mad as a March hare referred to how hare’s would leap around in a crazy fashion during breeding season, which was thought incorrectly to occur only during March. The March Hare was also a character in the Alice in Wonderland stories, appearing the the tea party scene in Through the Looking Glass. Since Carroll included both a Mad Hatter and a March Hare character, using the two variations of this idiom, it seems fairly clear that his initial inspiration was idiomatic. 3Ammer, Christine. American Heritage Dictionary of Idioms. Boston: Houghton Mifflin Harcourt, 2013.,4Ayto, John. Oxford Dictionary of English Idioms. Oxford: Oxford U, 2010.

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