"The phrase “mad as a hatter” has its origins in the 18th and 19th centuries, linked to the dangerous working conditions of hat makers. During this time, many hatters used mercury nitrate in the process of curing felt for hats. Prolonged exposure to mercury caused a condition now known as mercury poisoning, which affected the nervous system and led to symptoms such as tremors, mood swings, and erratic behavior. These effects were so common among hat makers that people began associating their unusual behavior with the profession, coining the term “mad as a hatter.” Though often linked to Lewis Carroll’s Alice’s Adventures in Wonderland, the phrase was in use well before the book’s publication"