Mad Hatter’s disease was a real illness, an old name for long-term mercury poisoning that once ran through the hat-making trade. The phrase “mad as a hatter” described real workers whose mercury exposure changed how they moved, thought, and behaved.1HISTORY. Where did the phrase “mad as a hatter” come from? The poisoning outlived the hat factories, though, and it still harms millions of people who never make a hat.2PubMed. Global Burden of Disease of Mercury Used in Artisanal Small-Scale Gold Mining
How Mercury Vapor Gets Into the Brain
The form of mercury, and the way it enters your body, decides how dangerous it is. Liquid mercury that is swallowed or touched is poorly absorbed and carries little risk.3PubMed Central. Toxic Effects of Mercury on the Cardiovascular and Central Nervous Systems As a vapor, the same metal is readily absorbed through the lungs.4PubMed Central. Toxic Effects of Mercury on the Cardiovascular and Central Nervous Systems About 80% of the mercury vapor you breathe in passes into your blood, and the blood carries it to every organ in the body.5Journal of Preventive Medicine and Public Health. Human Exposure and Health Effects of Inorganic and Elemental Mercury Liquid mercury gives off vapor at room temperature, enough to reach about 100 times the safe level in the air, so a spill hidden in floor cracks can poison a room.6Journal of Human Hypertension. Toxicity of mercury
The brain takes the worst of it. Mercury vapor dissolves in fat, so it slips through cell walls and through the barrier that normally protects the brain.7Journal of Preventive Medicine and Public Health. Human Exposure and Health Effects of Inorganic and Elemental Mercury It stays as vapor in the blood briefly before changing form, and that is long enough for a large amount to reach the brain.8Journal of Preventive Medicine and Public Health. Human Exposure and Health Effects of Inorganic and Elemental Mercury Once inside, the changed mercury gets trapped and builds up in brain tissue.9Journal of Preventive Medicine and Public Health. Human Exposure and Health Effects of Inorganic and Elemental Mercury There, it latches onto proteins the body needs to protect and run its cells, disrupting how those cells work and survive.10PubMed Central. Sulfhydryl groups as targets of mercury toxicity In one man, mercury was still found in nerve cells 16 years after poisoning at work.11PubMed. Persistent mercury in nerve cells 16 years after metallic mercury poisoning Small daily doses add up because the brain holds onto mercury, and symptoms creep in over months, so workers and their families often missed the cause.
Mercury comes in three forms with different harms. Mercury salts, which dissolve in water, mainly irritate the gut and damage the kidneys.12Journal of Human Hypertension. Toxicity of mercury Organic mercury, such as the kind in fish, crosses into the brain and causes nerve damage.13Journal of Human Hypertension. Toxicity of mercury Mad Hatter’s disease is specifically the metallic-vapor form, which is why breathing it in at work was the danger.
Why Hat Makers Were Poisoned
Hat makers treated animal fur with nitric acid and mercury nitrate to help turn it into felt.14GSA Abstracts with Programs. ANTHROPOGENIC IMPACT OF AN HISTORIC HAT FACTORY ON MERCURY AND TRACE ELEMENTS CONCENTRATIONS OF SURROUNDING TOPSOIL, DANBURY CT The orange-colored mercury solution gave the step its name, “carroting.”15Centers for Disease Control and Prevention. NIOSH Backgrounder: Alice’s Mad Hatter & Work-Related Illness Workers were exposed to mercury at each step of making a hat.16Public Health Image Library. Public Health Image Library ID 6810 In the 1930s, about 1 in 10 hat-factory workers in Connecticut had chronic, disabling mercury poisoning.17Public Health Image Library. Public Health Image Library ID 6810
Fur was brushed with warm mercury solution, then dried and steamed, which released vapor. Shops were often poorly ventilated, so workers breathed it for years.
The trade was huge. Danbury, Connecticut, called the “hat capital of the world,” made hats for over 150 years, from the 1780s to the 1940s.18GSA Abstracts with Programs. ANTHROPOGENIC IMPACT OF AN HISTORIC HAT FACTORY ON MERCURY AND TRACE ELEMENTS CONCENTRATIONS OF SURROUNDING TOPSOIL, DANBURY CT At its peak, Danbury’s factories turned out 5 million hats a year.19GSA Abstracts with Programs. ANTHROPOGENIC IMPACT OF AN HISTORIC HAT FACTORY ON MERCURY AND TRACE ELEMENTS CONCENTRATIONS OF SURROUNDING TOPSOIL, DANBURY CT A survey of exposed U.S. hatters found mostly nervous-system symptoms, including shaking during movement.20Wikipedia. Erethism
Families and neighbors could be affected too. Workers carried mercury home on clothes, hands, and hair, so the exposure did not necessarily end when the shift did. Small hat shops were often in or beside homes, so vapor and residue could spread through living space. That is one reason mercury poisoning is now treated as a household and community concern as well as a job hazard.
Symptoms of Mad Hatter’s Disease
Doctors call the mood and personality changes “erethism,” a word you may see in medical writing.21PubMed. Erethism Mercurialis and Reactions to Elemental Mercury They include restlessness, irritability, trouble sleeping, mood swings, poor concentration, and memory loss.22PubMed. Erethism Mercurialis and Reactions to Elemental Mercury Some people become extremely shy, while others become easily excited.23Industrial Health. Occupational and environmental toxicology of mercury and its compounds Depression and tiredness are common, and severe cases can bring confusion and hallucinations.24PubMed Central. Mercury Toxicity and Treatment: A Review of the Literature
The “mad” label was misleading. Many hatters were not raving but painfully shy, anxious, and jumpy, and shaking hands made them seem drunk or unwell.
The shaking is one of the most recognizable signs. A jerky tremor when holding a position is among the most common signs of breathing metallic mercury.25Canadian Journal of Neurological Sciences. Mercury and Movement Disorders: The Toxic Legacy Continues At higher exposures, small muscle twitches are broken every few minutes by coarse shaking.26PubMed Central. Mercury Toxicity and Treatment: A Review of the Literature Among people poisoned by skin-lightening creams, 9 in 10 had tremor and 8 in 10 had memory decline.27PubMed Central. Characteristics of Mercury Intoxication Induced by Skin-lightening Products
Inflamed gums and heavy drooling have been described in mercury poisoning.28PubMed Central. Mercury Toxicity and Treatment: A Review of the Literature In young children, mercury can cause “pink disease,” with painful, reddened hands and feet. The mix of tremor, mood change, and gum trouble together points more strongly to mercury than any one sign alone.
Early signs are often vague, such as tiredness, poor sleep, irritability, and a slight tremor in the hands, so they are easy to wave off. With continued exposure the tremor can spread and grow coarser, and thinking and mood problems can deepen.
Plenty of other things can look like this. Tremor and anxiety also occur with thyroid problems, caffeine, and some medicines, and memory and mood changes overlap with depression and other conditions. Without known mercury exposure, a doctor will usually check common causes first.
Where People Get Mercury Poisoning Today
Gold mining is today’s hatting. Small-scale gold miners mix mercury with ore so it grabs the gold.29UNEP – UN Environment Programme. Mercury has long poisoned gold miners. This new strategy is helping change that They then heat the mix, often with a torch or on a stove, to boil off the mercury and leave gold.30PubMed Central. The Mercury Problem in Artisanal and Small‐Scale Gold Mining The heating releases mercury vapor right where miners breathe.31UNEP – UN Environment Programme. Mercury has long poisoned gold miners. This new strategy is helping change that Of 14 to 19 million such miners worldwide, a quarter to a third, 3.3 to 6.5 million people, have moderate mercury vapor poisoning.32PubMed. Global Burden of Disease of Mercury Used in Artisanal Small-Scale Gold Mining
The vapor is invisible with no noticeable smell. Miners often burn the mix in open air or in a home kitchen, so family members, including children, breathe it too. Mercury also settles into nearby soil and water, so the harm is not limited to the person doing the work.
Household sources matter too. Some skin-lightening creams contain mercury and can cause poisoning with tremor, memory loss, and anxiety.33PubMed Central. Characteristics of Mercury Intoxication Induced by Skin-lightening Products A broken fever thermometer released enough vapor to poison three children in one home.34Monatsschrift Kinderheilkunde. ACRODYNIA (PINK DISEASE, FEERS DISEASE) A spill that sinks into floor cracks can keep giving off vapor.35Journal of Human Hypertension. Toxicity of mercury If you use imported lightening or “whitening” creams, check the label for mercury, calomel, or mercurous chloride, and stop using any that list it.
If you break a mercury thermometer, keep children and pets out and open windows to air the room. Never vacuum or sweep, which spreads tiny droplets and vapor. Use stiff paper or tape to collect the beads into a sealed container, and contact your local health or poison center for disposal guidance.
Most new thermometers are digital and contain no mercury. Old thermostats, barometers, and some older thermometers may still hold it. Compact fluorescent bulbs contain a tiny amount, far less than a thermometer.
Children Are More Sensitive to Mercury
The brain of a child under 5 is much more sensitive to long-term mercury than an adult’s.36Monatsschrift Kinderheilkunde. ACRODYNIA (PINK DISEASE, FEERS DISEASE) Children can have severe symptoms with urine mercury well below 50 µg/L, and one child was seriously ill at just 6.3 µg/L.37Monatsschrift Kinderheilkunde. ACRODYNIA (PINK DISEASE, FEERS DISEASE) Adults exposed at work, by contrast, have been allowed urine levels up to 200 µg/L.38Monatsschrift Kinderheilkunde. ACRODYNIA (PINK DISEASE, FEERS DISEASE) Mercury vapor also crosses the placenta, so pregnancy is another time to avoid exposure.39Journal of Preventive Medicine and Public Health. Human Exposure and Health Effects of Inorganic and Elemental Mercury
Children breathe faster for their size and spend more time close to the ground, so they may take in more vapor than adults in the same room. Because they are small, the same amount of mercury makes a bigger dose per pound of body weight.
Children play on floors, where vapor from settled droplets is strongest. Their symptoms can look like fussiness, rash, or poor sleep, which delays diagnosis, so tell the doctor about any recent spill if a child becomes unwell.
How Mercury Poisoning Is Diagnosed and Treated
Urine is the preferred test for most metallic mercury exposure because the body clears it through the kidneys, so urine mercury best reflects long-term exposure.40PubMed Central. Characteristics and treatment of elemental mercury intoxication: A case series Blood mercury reflects more recent exposure and is more useful after a short, heavy one.41PubMed. Interpreting Mercury in Blood and Urine of Individual Patients Organic mercury from fish leaves mainly through stool, so it barely shows in urine.42PubMed Central. Characteristics and treatment of elemental mercury intoxication: A case series In one woman with a diagnosis of erethism, blood mercury was over 100 µg/L.43PubMed. Erethism Mercurialis and Reactions to Elemental Mercury
To prepare for a visit, list possible sources: job, hobbies, creams, spills, home remedies. Note when symptoms began and whether they ease away from home or work. Ask whether a 24-hour urine collection is needed, which means saving all urine for a day.
The first step in treatment is ending the exposure. Doctors may then use chelation, drugs that bind mercury so the body passes it in urine.44PubMed. Chelation therapy in intoxications with mercury, lead and copper The two common ones, DMSA and DMPS, can be taken by mouth and are gentler than the older drug BAL.45PubMed. Chelation therapy in intoxications with mercury, lead and copper In people poisoned by skin creams, DMPS lowered urine mercury and symptoms improved.46PubMed Central. Characteristics of Mercury Intoxication Induced by Skin-lightening Products For long-term poisoning, though, it’s not proven that these drugs improve health outcomes beyond lowering mercury.47PubMed Central. The role of chelation in the treatment of arsenic and mercury poisoning Some patients briefly get worse during treatment before improving.48PubMed. Hyperintense lesions in brain MRI after exposure to a mercuric chloride-containing skin whitening cream
At-home “detox” kits are a bad idea. The drugs that pull mercury out are prescription medicines with real side effects. Provoked urine tests sold online can falsely suggest poisoning, and proper testing and treatment need a doctor or poison center.
Can People Recover From Mercury Poisoning
Most people recover at least partly after exposure ends.49PubMed. Elemental mercury neurotoxicity and clinical recovery of function: A review of findings, and implications for occupational health Shaking and movement problems often improve a lot within 2 to 6 months.50PubMed. Elemental mercury neurotoxicity and clinical recovery of function: A review of findings, and implications for occupational health Memory, mood, and thinking problems recover more slowly and less completely.51PubMed. Elemental mercury neurotoxicity and clinical recovery of function: A review of findings, and implications for occupational health One man poisoned at work recovered slowly, with mercury still in his brain years later.52PubMed. Persistent mercury in nerve cells 16 years after metallic mercury poisoning In some cases, brain scan changes cleared along with symptoms within about 4 months.53PubMed. Hyperintense lesions in brain MRI after exposure to a mercuric chloride-containing skin whitening cream How well someone recovers depends on how long and how heavily they were exposed, and how quickly the source was removed. Improvement tends to be gradual, so people often notice the shaking easing before they notice better memory or mood.
History of the Phrase and the Ban
“Mad as a hatter” appeared in print by 1829, decades before Alice’s Adventures in Wonderland.54Wikipedia. Mad as a hatter Lewis Carroll’s 1865 Hatter drew on a saying people already knew.55World Wide Words. Mad as a Hatter: Origin and History of the Phrase Some film versions give the Hatter red-orange hair, a nod to the orange mercury solution.56Centers for Disease Control and Prevention. NIOSH Backgrounder: Alice’s Mad Hatter & Work-Related Illness
Carroll never said the Hatter was poisoned, and the character’s chatter fits the well-known saying. His silliness differs from real hatters’ shyness and tremor. The phrase likely spread because the illness was familiar in hat towns.
U.S. Public Health Service studies of sick hatters in the 1930s helped push for change.57Public Health Image Library. Public Health Image Library ID 6810 A 1941 agreement among workers, industry, and government banned mercury in U.S. hat making.58Public Health Image Library. Public Health Image Library ID 6810 Medical studies alone hadn’t stopped it, though; mercury was needed for World War II detonators.59PubMed. Were the hatters of New Jersey “mad”?
The legacy lingers. Around Danbury, old factory mercury still sits in river sediments and upland soil today.60Wesleyan University Magazine. Something in the Water Big floods have washed that mercury downstream toward Long Island Sound.61Wesleyan University Magazine. Something in the Water