The term mad as a hatter, or variations of this phrase, is generally used to refer to a crazy person. The term is believed to have originated during the 18th century when the production of felt for hats used mercury.
Unfortunately for the workers in these factories, the exposure to mercury over time caused mental illnesses and tremors, among other ailments. It was not until the Victorian Era that the effects of working with mercury became well known in society, leading to the popular saying ‘mad as a hatter’ or ‘the hatters’ shakes.’
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