Mercury poisoning, also known as the "Mad Hatter Disease", affected many hat makers in the 18th-19th centuries. Mercury was used in the felting process to make hats, exposing workers through inhalation of mercury vapors. long-term low-level exposure caused neurological symptoms like tremors and irrational behavior. Known as the "Danbury Shakes", mercury poisoning in the hat industry of Danbury, CT was finally banned in 1941 after unions repeatedly called attention to the health risks. While treatment can help manage symptoms, heavy or prolonged exposure can cause permanent neurological damage.

1. Mad Hatter Disease

2. • In the 18th and 19th centuries, hats
were often made from the fur of
small animals (such as rabbits or
beavers) which first underwent a
felting process.
• This process involved using a
mixture to separate the fur from
the skin and keep the hair together.
• The mixture contained mercuric
nitrate—i.e. mercury. Since the
mixture was orange, the process
was called “carroting.”
“Carroting”

3. • The skins were then dried in an
oven before being stretched over a
bar in a cutting machine.
• The pelts were then sliced off in
thin shreds and layered onto a
conical mould, where they would
be pressed and shrunk with steam
and hot water.
• The resulting felt could then be
dyed and made into fine hats.
Felting Process

4. • Use of mercury in hatmaking is
thought to have originated with the
Huguenots in 17th century France
and eventually carried to England.
• The effects of mercury exposure
were already known, but
nonetheless milliners often worked
in confined spaces, without
ventilation or protective gear of
any kind.
• The expression “mad as a hatter”
can be traced back as far as 1829.
Mercury Exposure

5. • Exposure to mercury can cause a
neurological disorder known as
erethism.
• Erethism is characterized by
behavioral changes such as
irritability, low self-confidence,
depression, apathy, shyness and
timidity.
• In some extreme cases of prolonged
exposure to mercury vapors, delirium,
personality changes and memory loss
can also occur.
Mercury Poisoning

6. • People with erethism often have
difficulty with social interactions.
• There are physical problems associated
with mercury poisoning as well, including
a decrease in physical strength,
headaches, general pain, and tremors, as
well as an irregular heartbeat.
• Other possible symptoms include: kidney
damage, sweating, loss of hearing, red
fingers and toes, red cheeks, insomnia.
Mercury Poisoning

7. • Danbury, CT boasted of being the
“Hat City of the World” from the
1850s until WW2.
• At the peak, around 5 million hats
were produced in Danbury each
year.
• The Connecticut State Board of
Health monitored the effect of
mercury in Danbury’s hat-making
factories in the 1880s and 1890s, but
as long as the carroting process did
not affect the health of the general
“Danbury Shakes”
The Mallory Hat Factory in
Danbury, CT circa 1884

8. • The tremors from mercury poisoning
became so deeply associated with the
industry in the area that they were
dubbed the “Danbury Shakes.”
• According to a study in 1922:
➥ “...[Of] 100 union hatters of Danbury,
Conn., examined by experts, 43 had
mercury poisoning…
Boys 20 and 21 years old are already
so badly poisoned that their hands
shake continually, while many of the
men who have served longer at the
trade cannot even feed themselves.”
“Danbury Shakes”

9. • Through their unions, Danbury hatters
persistently called for call an investigation
into their work conditions and exposure to
mercury vapor.
• Mercury poisoning was added to the state
Workmen’s Compensation Act of 1913 and
was recognized by the state as an
occupational hazard in 1919.
• But it was not until 1937 that a government
study was undertaken, which found a high
incidence of mercury poisoning among
workers in the hat-making industry.
“Danbury Shakes”

10. • The 1937 study also noted that alcohol
and tobacco use were not to blame for
their symptoms, as had been alleged by
some manufacturers and insurers in
court cases.
• On December 1, 1941, Governor Robert
A. Hurley announced Connecticut’s ban
on the use of mercury, saying that “it
was possible to manufacture good fur
felt hats without making physical
wrecks out of hundreds of workers.”
• Hydrogen peroxide replaced the use of
mercury.
“Danbury Shakes”

11. • For many years after 1941, Danbury’s hatters
celebrated the mercury ban every December
1st.
• The mercury in Danbury did not simply
disappear, though - high levels are still evident
in the ground upon which the factories stood
and in the sediment of local rivers.
• In 2003, one factory site was planted with
Eastern cottonwood trees that had been
genetically engineered to absorb mercury from
the soil.
• This process, called phytoremediation, is
controversial because the trees emit traces of
“Danbury Shakes”

12. • 1829: First description of symptoms is published
in St. Petersburg, Russia.
• 1860: Detailed description of mercury poisoning
among New Jersey hatters appears in an article
by Addison Freeman, titled "Mercurial Disease
Among Hatters,” which is published in a local
medical journal.
➥ "A proper regard for the health of this class
of citizens demands that mercury should not
be used so extensively in the manufacture of
hats, and that if its use is essential, that the
hat finishers' room should be large, with a
high ceiling, and well-ventilated."
Timeline

13. • 1869: French Academy of Medicine demonstrates
the health hazards posed to hatmakers.
• 1874: Alternatives to mercury use in hatmaking
become available.
• 1888: A hydrochloride-based process is patented in
the U.S. - but is ignored.
• 1898: Legislation is passed in France to protect
hatmakers from the risks of mercury exposure.
• 1934: U.S. Public Health Service estimates that 80%
of American felt makers have mercurial tremors.
• 1941: U.S. hatmakers voluntarily adopt a ban on
mercury use - primarily due to mercury being
diverted to the war effort, not to protect workers.
Timeline

14. • Some of the toxic effects of mercury are
partially or wholly reversible, either
through chelation therapy or through
natural elimination of the metal after
exposure has been discontinued.
• However, heavy or prolonged exposure
can do irreversible damage, in
particular in fetuses, infants, and young
children who are still developing.
• Autopsy findings point to a half-life of
inorganic mercury in human brains of
27.4 years.
Treatment and Prognosis

15. • There is no “cure” for mercury poisoning.
The best way to treat mercury poisoning is to
stop your exposure to the metal.
• Decontamination requires removal of
clothes, washing skin with soap and water,
and flushing the eyes with saline solution as
needed.
Treatment and Prognosis

16. • Chelation therapy: Chelating agents
are drugs that remove the metal
from your organs and help your
body dispose of them.
• Chelation therapy may have limited
success in treating prolonged
exposure to mercury.
• Long term, continued treatment is
necessary to manage the physical
and neurological effects of mercury
poisoning.
Treatment and Prognosis

17. • Tim Burton’s 2010 version of Alice in Wonderland
stars Johnny Depp as the Mad Hatter.
• The orange marks on the Mad Hatter’s skin, as well
as the deep orange color of his hair, recall the
symptoms associated with carroting.
• In a 2009 interview with the Los Angeles Times,
Johnny Depp said that he was aware of the
implications of the Hatter’s behavior:
➥ "I think [the Mad Hatter] was poisoned – very,
very poisoned. And I think it just took [e]ffect in
all his nerves. It was coming out through his hair
and through his fingernails, through his eyes."
Alice in Wonderland Character