Mad As a Hatter (Origin)

What Is the Origin of the Saying "Mad As a Hatter"?

To be as mad as a hatter means to be crazy or to behave unpredictably.

The term comes from the hat-making industry in the middle ages, which used the highly toxic mercury nitrate in the hat�s rim. The people who made these hats would often suffer poisoning which would make them act oddly. Therefore, many hatters were assumed to be crazy.

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