As We Say It

"The new head of marketing is completely mad as a hatter." You say it casually — maybe with a hint of affection, maybe with genuine alarm — and everyone understands: the person in question is eccentric, erratic, possibly unhinged, and almost certainly entertaining at company events.

Most people, when they hear this phrase, think immediately of Lewis Carroll's Mad Hatter from Alice's Adventures in Wonderland, published in 1865. The image is so iconic — the oversized top hat, the manic tea party, the unanswerable riddles — that Carroll is widely assumed to have invented both the character and the phrase.

He didn't. The phrase was old when Carroll found it. And the reality behind it was far darker than anything in Wonderland.

The Wrong Version

The most common misconception is that Carroll coined the expression. He didn't even use it. At no point in Alice's Adventures in Wonderland is the character referred to as "the Mad Hatter." He's simply "the Hatter." The "mad" part was added by readers, by illustrators, and eventually by a century of adaptations — Disney chief among them. Carroll knew the phrase existed. He was playing on it. But the words "mad as a hatter" don't appear anywhere in the book.

There's also a competing theory involving a completely different kind of hatter. Some etymologists have suggested that "mad as an adder" — adder being a venomous snake — was the original phrase, later corrupted to "hatter" through regional pronunciation. It's a reasonable-sounding theory. The evidence for it, unfortunately, is almost entirely nonexistent.

The Real Story

In the seventeenth, eighteenth, and nineteenth centuries, the process of making felt hats required a chemical called mercurous nitrate. The substance was used in a process called "carroting" — so named because it turned animal fur a bright orange — which softened and matted the fibres so they could be pressed into felt. Hatters worked with this mercury compound every day, in poorly ventilated workshops, breathing in the fumes and absorbing the poison through their skin.

Mercury is a neurotoxin. Chronic exposure to mercury vapour causes a condition that nineteenth-century doctors called "erethism" — from the Greek erethismos, meaning irritation. The symptoms were devastating and, to the casual observer, looked exactly like madness: tremors so severe that hatters could barely hold a cup (this was called "hatter's shakes"), extreme mood swings, memory loss, paranoia, slurred speech, social withdrawal, and sudden, unpredictable rages. In advanced cases, the teeth fell out. The gums turned blue. The personality disintegrated entirely.

The hatters knew something was wrong. They watched their colleagues deteriorate. They gave it names — "the trembles," "the danbury shakes" (after Danbury, Connecticut, the centre of the American hat industry). But the cause wasn't understood until well into the twentieth century, and the trade continued to use mercury compounds for decades after the link to neurological damage was established.

The phrase itself predates Carroll by at least three decades. The earliest known use in print comes from Blackwood's Edinburgh Magazine in 1829: "The man was as mad as a hatter." By the 1830s, it was common enough that Thomas Chandler Haliburton used it in his 1836 work The Clockmaker — a Canadian humour book — apparently confident that his readers would recognise it immediately. By the time Carroll wrote Alice in the 1860s, "mad as a hatter" was such a well-known expression that he could build an entire character around it without needing to explain the joke.

The scale of the problem was staggering. In the hat-making centres of England — Stockport, Denton, and parts of London — mercury poisoning was so common among hatters that it was simply considered an occupational hazard, like a coal miner's cough or a factory worker's deafness. Nobody banned it. Nobody compensated the workers. The hats were too profitable, and the hatters were too replaceable.

It wasn't until 1941 that the United States Public Health Service finally banned the use of mercury in the felt hat industry. France had restricted it somewhat earlier. Britain, characteristically, took its time. By the mid-twentieth century, the felt hat was falling out of fashion anyway, replaced by newer styles that didn't require mercury processing. The disease disappeared not because anyone decided to protect the workers, but because the market moved on.