Mad hatter disease

Mercury poisoning, chronic (neurological symptomatology)
Classification and external resources
Specialty emergency medicine
ICD-10 T56.1
ICD-9-CM 985.0
DiseasesDB 8057
MedlinePlus 002476
eMedicine emerg/813
MeSH D020262

Mad hatter disease, or mad hatter syndrome, was an occupational disease among hatmakers, caused by chronic mercury poisoning. It affected those whose felting work involved prolonged exposure to mercury vapors. The neurotoxic effects included tremor and the pathological shyness and irritability characteristic of erethism.

Use of inorganic mercury in the form of mercuric nitrate to treat the fur of small animals for the manufacture of felt hats seems to have begun in 17th-century France and from there spread to England by the end of the century with the Huguenots. By the Victorian era the hatters' condition had become proverbial, as reflected in popular expressions like "mad as a hatter" and "hatters' shakes". Similar phenomena had been described in St Petersburg, Russia, in 1829. In France, the National Academy of Medicine described the health hazards in 1869, and in 1898 a law was passed to protect hatmakers from the risks of mercury exposure. In Britain, mercury poisoning among hatters had become a rarity by the turn of the 20th century. In the United States, where the occupational illness was thoroughly described in New Jersey in 1860, the practice continued until 1941; mercury poisoning in the hatmaking industries of Danbury, Connecticut gave rise to the expression "Danbury shakes". Hatmakers in Tuscany, Italy, were also affected and exposed workers received financial compensation.

Although Lewis Carroll's iconic Mad Hatter character in Alice's Adventures in Wonderland has often been linked to the occupational hazards of hatmaking, it is thought that the character was directly inspired by the eccentric furniture dealer Theophilus Carter.

Origins and history

Some of the steps in the manufacture of felt hats are illustrated in this image from 1858.
A man working in hat manufacture with no protective equipment, putting him at risk for mercury poisoning

Especially in the 19th century, inorganic mercury in the form of mercuric nitrate was commonly used in the production of felt for hats.[1] During a process called carroting, in which furs from small animals such as rabbits, hares or beavers were separated from their skins and matted together, an orange-colored solution containing mercuric nitrate was used as a smoothing agent. The resulting felt was then repeatedly shaped into large cones, shrunk in boiling water and dried.[2] In treated felts, a slow reaction released volatile free mercury.[3] Hatters (or milliners) who came into contact with vapours from the impregnated felt often worked in confined areas.[4]

Use of mercury in hatmaking is thought to have been adopted by the Huguenots in 17th-century France,[2][5] at a time when the dangers of mercury exposure were already known. This process was initially kept a trade secret in France, where hatmaking rapidly became a hazardous occupation. At the end of the 17th century the Huguenots carried the secret to England, following the revocation of the Edict of Nantes. During the Victorian era the hatters' malaise became proverbial, as reflected in popular expressions like "mad as a hatter" (see below) and "the hatters' shakes".[2][5][6]

The first description of symptoms of mercury poisoning among hatters appears to have been made in St Petersburg, Russia, in 1829.[7] In the United States, a thorough occupational description of mercury poisoning among New Jersey hatters was published locally by Addison Freeman in 1860.[8][9] Adolph Kussmaul's definitive clinical description of mercury poisoning published in 1861 contained only passing references to hatmakers, including a case originally reported in 1845 of a 15-year-old Parisian girl, the severity of whose tremors following two years of carroting prompted opium treatment.[8] In Britain, the toxicologist Alfred Swaine Taylor reported the disease in a hatmaker in 1864.[8]

In 1869, the French Academy of Medicine demonstrated the health hazards posed to hatmakers. Alternatives to mercury use in hatmaking became available by 1874. In the United States, a hydrochloride-based process was patented in 1888 to obviate the use of mercury, but was ignored.[10]

In 1898, legislation was passed in France to protect hatmakers from the risks of mercury exposure. By the turn of the 20th century, mercury poisoning among British hatters had become a rarity.[6][11]

Picture postcard of a hat factory in Danbury (postmarked 1911)

In the United States, the mercury-based process continued to be adopted until as late as 1941, when it was abandoned mainly due to the wartime need for the heavy metal in the manufacture of detonators.[8][10] Thus, for much of the 20th century mercury poisoning remained common in the U.S. hatmaking industries, including those located in Danbury, Connecticut (giving rise to the expression the "Danbury shakes").[6][7]

Another 20th-century cohort of affected hatmakers has been studied in Tuscany, Italy.[12][13]

Symptoms and effects

The man affected is easily upset and embarrassed, loses all joy in life and lives in constant fear of being dismissed from his job. He has a sense of timidity and may lose self control before visitors. Thus, if one stops to watch such a man in a factory, he will sometimes throw down his tools and turn in anger on the intruder, saying he cannot work if watched. Occasionally a man is obliged to give up work because he can no longer take orders without losing his temper or, if he is a foreman, because he has no patience with men under him. Drowsiness, depression, loss of memory and insomnia may occur, but hallucinations, delusions and mania are rare.
The most characteristic symptom, though it is seldom the first to appear, is mercurial tremor. It is neither as fine nor as regular as that of hyperthyroidism. It may be interrupted every few minutes by coarse jerky movements. It usually begins in the fingers, but the eyelids, lips and tongue are affected early. As it progresses it passes to the arms and legs, so that it becomes very difficult for a man to walk about the workshop, and he may have to be guided to his bench. At this stage the condition is so obvious that it is known to the layman as "hatter's shakes."

Buckell et al, Chronic Mercury Poisoning (1946)[7]

Further information: Erethism

Effects of chronic occupational exposure to mercury, such as that commonly experienced by affected hatters, include mental confusion, emotional disturbances, and muscular weakness.[14] Severe neurological damage and kidney damage can also occur.[4] Neurological effects include Korsakoff's dementia and erethism (the set of neurological symptoms characteristically associated with mercury poisoning). Signs and symptoms can include red fingers, red toes, red cheeks, sweating, loss of hearing, bleeding from the ears and mouth, loss of appendages such as teeth, hair, and nails, lack of coordination, poor memory, shyness, insomnia, nervousness, tremors, and dizziness.[4] A survey of exposed U.S. hatters revealed predominantly neurological symptomatology, including intention tremor.[7] After chronic exposure to the mercury vapours, hatters tended to develop characteristic psychological traits, such as pathological shyness and marked irritability (box).[2] Such manifestations among hatters prompted several popular names for erethism, including "mad hatter disease",[14] "mad hatter syndrome",[15][16] "hatter's shakes" and "Danbury shakes".

Hatters of New Jersey

The experience of hatmakers in New Jersey is well documented and has been reviewed by Richard Wedeen.[8] In 1860, at a time when the hatmaking industry in towns such as Newark, Orange and Bloomfield was growing rapidly, a physician from Orange called J. Addison Freeman published an article titled "Mercurial Disease Among Hatters" in the Transactions of the Medical Society of New Jersey. This groundbreaking paper provided a clinical account of the effects of chronic mercury poisoning among the workforce, coupled with an occupational description of the use of mercuric nitrate during carroting and inhalation of mercury vapour later in the process (during finishing, forming and sizing). Freeman concluded that "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."[9] Freeman's call for prevention went unheeded.

In 1878, an inspection of 25 firms around Newark conducted by Dr L. Dennis on behalf of the Essex County Medical Society revealed "mercurial disease" in 25% of 1,589 hatters. Dennis recognized that this prevalence figure was probably an underestimate, given the workers' fear of being fired if they admitted to being diseased. Although Dennis did recommend the use of fans in the workplace he attributed most of the hatters' health problems to alcohol abuse (thus using the stigma of drunkenness in a mainly immigrant workforce to justify the unsanitary working conditions provided by employers).[8][17]

The surprise is that men can be induced to work at all in such death producing enclosures. It is hard to believe that men of ordinary intelligence could be so indifferent to the ordinary laws of health... It does not seem to have occurred to them that all the efforts to keep up wages... [are] largely offset by the impairment of their health, due to neglect of proper hygienic regulations of their workshops... And when the fact of the workmen in the sizing room, who stand in water, was mentioned, and the simple and inexpensive means by which it could be largely avoided was spoken of, the reply was that it would cost money and hat manufacturers did not care to expend money for such purposes, if they could avoid it.

Bishop, Annual Report of the Bureau of Statistics of Labor and Industries of New Jersey (1890)[18]

Some voluntary reductions in mercury exposure were implemented after Lawrence T. Fell, a former journeyman hatter from Orange who had become a successful manufacturer, was appointed Inspector of Factories in 1883. In the late nineteenth century, a pressing health issue among hatters was tuberculosis. This deadly communicable disease was rife in the extremely unhygienic wet and steamy enclosed spaces in which the hatters were expected to work (in its annual report for 1889, the New Jersey Bureau of Labor and Industries expressed incredulity at the conditions—see box). Two-thirds of the recorded deaths of hatters in Newark and Orange between 1873 and 1876 were caused by pulmonary disease, most often in men under 30 years of age, and elevated death rates from tuberculosis persisted into the twentieth century. Consequently, public health campaigns to prevent tuberculosis spreading from the hatters into the wider community tended to eclipse the issue of mercury poisoning. For instance, in 1886 J. W. Stickler, working on behalf of the New Jersey Board of Health, promoted prevention of tuberculosis among hatters, but deemed mercurialism "uncommon", despite having reported tremors in 15–50% of the workers he had surveyed.[8][19]

While hatters seemed to regard the shakes as an inevitable price to pay for their work rather than a readily preventable disease, their employers professed ignorance of the problem. In a 1901 survey of 11 employers of over a thousand hatters in Newark and Orange, the head of the Bureau of Statistics of New Jersey, William Stainsby, found a lack of awareness of any disease peculiar to hatters apart from tuberculosis and rheumatism (though one employer remarked that "work at the trade develops an inordinate craving for strong drink").[8][20]

By 1934 the U.S. Public Health Service estimated that 80% of American felt makers had mercurial tremors. Nevertheless, trade union campaigns (led by the United States Hat Finishers Association, originally formed in 1854) never addressed the issue and, unlike in France, no relevant legislation was ever adopted in the United States. Instead, it seems to have been the need for mercury in the war effort that eventually brought to an end the use of mercuric nitrate in U.S. hatmaking; in a meeting convened by the U.S. Public Health Service in 1941, the manufacturers voluntarily agreed to adopt a readily available alternative process using hydrogen peroxide.[8]

"Mad as a hatter"

While the name of Lewis Carroll's Mad Hatter may contain an allusion to the hatters' syndrome, the character itself appears to have been based on an eccentric furniture dealer.
Main article: Mad as a hatter

Although the expression "mad as a hatter" was associated with the syndrome,[21] the origin of the phrase is uncertain. Lewis Carroll's iconic Mad Hatter character in Alice's Adventures in Wonderland displays markedly eccentric behavior, which includes taking a bite out of a teacup.[22] While Carroll would have been familiar with the phenomenon of dementia among hatters, it is thought that the literary character was directly inspired by Theophilus Carter, an eccentric furniture dealer who did not show signs of mercury poisoning.[2]

Actor Johnny Depp has said of his portrayal of a carrot-orange haired Mad Hatter in Tim Burton's 2010 film, Alice in Wonderland that the character "was poisoned ... and it was coming out through his hair, through his fingernails and eyes".[23]

See also


  1. Lagassé, Paul, ed. (2008). Columbia Encyclopedia. Columbia University Press.
  2. 1 2 3 4 5 Waldron HA (1983). "Did the Mad Hatter have mercury poisoning?". British Medical Journal (Clinical Research Edition). 287 (6409): 1961. doi:10.1136/bmj.287.6409.1961. PMC 1550196Freely accessible. PMID 6418283.
  3. Neal, PA; Jones, RR; Bloomfield, JJ; Dallavalle, JM; Edwards, TI (May 1937). "A study of chronic mercurialism in the hatter's fur-cutting industry". Public Health Bulletin: iv, 70. Retrieved 10 March 2013.
  4. 1 2 3 Mayz, Eusebio (1973). Mercury Poisoning: I. MSS Information Corporation. ISBN 0842270728.
  5. 1 2 Devine, Edward Thomas; Kellogg, Paul Underwood, eds. (1924). "The Survey". 51. Survey Associates: 457. Retrieved 10 March 2013. [Huguenot] craftsmen held the secret of making felt by treating fur with acid nitrate of mercury. In 1685 Louis XIV revoked the Edict [of Nantes] and they fled carrying the secret with them ... I suspect that the inventor of the process of making these "beaver hattes" was a Huguenot; certainly the secret passed into Huguenot hands, and at the revocation of the Edict of Nantes, when the Huguenots fled to England they carried with them the secret of their process, established the trade there, and for almost a century thereafter the French were dependent on England for their felt.
  6. 1 2 3 Bigham, Gary; Henry, Betsy; Bessinger, Brad (2005). "Mercury – A Tale of Two Toxins". Natural Resources & Environment. 19 (4): 26–30, 71. JSTOR 40924607.
  7. 1 2 3 4 Buckell, M; Hunter, D; Milton, R; Perry, KM (February 1993) [1946]. "Chronic mercury poisoning. 1946". British Journal of Industrial Medicine. 50 (2): 97–106. doi:10.1136/oem.50.2.97-a. PMID 8435354.
  8. 1 2 3 4 5 6 7 8 9 Wedeen, RP (1989). "Were the hatters of New Jersey 'mad'?". American Journal of Industrial Medicine. 16 (2): 225–33. doi:10.1002/ajim.4700160213. PMID 2672802. What remains most remarkable about the hatters of New Jersey is that they expressed no anger about their working conditions. Minutes of the Hat Finisher's Association of the City of Newark from 1853 to 1870 make no reference to hatters' shakes. Neither the hatters nor the public nor the medical community was mad about the health costs of industrial progress.
  9. 1 2 Freeman, J. Addison (1860). "Mercurial Disease Among Hatters". Transactions of the Medical Society of New Jersey: 61–64. During the winter of 1858–59 and following spring, there prevailed quite extensively among the hatters of Orange, Newark, Bloomfield, and Milburn a disease showing all the medical characteristics of Mercurial Salivation and Stomatitis. More than a hundred cases occurred in Orange alone. The usual symptoms were ulceration of the gums, loosening of the teeth, foeter of the breath, abnormal saliva, tremors of the upper extremities, or a shaking palsy,... the result of inhaling air impregnated with mercury vapor. (Cited in Wedeen, 1989)
  10. 1 2 Kitzmiller, Kathryn J. "The Not-So-Mad Hatter: occupational hazards of mercury". Chemical Abstracts Service. American Chemical Society. Retrieved 9 March 2013.
  11. Lee, WR (January 1968). "The history of the statutory control of mercury poisoning in Great Britain". British Journal of Industrial Medicine. 25 (1): 52–62. doi:10.1136/oem.25.1.52. PMC 1008662Freely accessible. PMID 4868255.
  12. Merler, E; Vineis, P; Alhaique, D; Miligi, L (May 1999). "Occupational cancer in Italy". Environmental Health Perspectives. 107 Suppl 2: 259–71. doi:10.2307/3434415. PMC 1566274Freely accessible. PMID 10350509.
  13. Merler, E; Boffetta, P; Masala, G; Monechi, V; Bani, F (November 1994). "A cohort study of workers compensated for mercury intoxication following employment in the fur hat industry". Journal of Occupational Medicine. 36 (11): 1260–4. doi:10.1097/00043764-199411000-00016. PMID 7861271.
  14. 1 2 Reber, Arthur; Allen, Rhiannon; Reber, Emily S. (2009). The Penguin Dictionary of Psychology. Penguin.
  15. "Mad Hatter syndrome". Stedman's Medical Dictionary. MediLexicon International Ltd. Retrieved 7 March 2013.
  16. Sadock, Benjamin James; Sadock, Virginia Alcott (2008). Kaplan & Sadock's Concise Textbook of Clinical Psychiatry. Lippincott Williams & Wilkins. pp. 78–79. ISBN 978-0-7817-8746-8. Retrieved 7 March 2013.
  17. Dennis, L (1878). "Hatting: As effecting the health of operatives". Report of the New Jersey State Board of Health. 2: 67–85. (Cited in Wedeen, 1989)
  18. Bishop, J (1890). Twelfth Annual Report of the Bureau of Statistics of Labor and Industries of New Jersey for the Year Ending October 31, 1889. Camden: F.F. Patterson. (Cited in Wedeen, 1989)
  19. Stickler, JW (1896). "Hatters' consumption". New York Medical Journal. 43: 598–602. (Cited in Wedeen, 1989)
    Stickler, JW (1887). "The hygiene of occupations. II. Diseases of hatters". Tenth Annual Report of the Board of Health of New Jersey and Report of the Bureau of Vital Statistics 1886. Trenton NJ: John L. Murphy Publishing Co. pp. 166–188. (Cited in Wedeen, 1989)
  20. Stainsby, W (1901). "Diseases and Disease Tendencies of Occupations: The Glass Industry and the Hatting Industry.". Twenty-Fourth Annual Report of the Bureau of Statistics of New Jersey. Trenton NJ. (Cited in Wedeen, 1989)
  21. Abbadie, Catherine; Karen E. Anderson; Jonathan M. Silver (2002). Ramachandran, V. S., ed. Encyclopedia of the Human Brain. Elsevier Science.
  22. Chambers Dictionary of Literary Characters. Chambers Harrap Publishers Ltd. 2004.
  23. Abramowitz, Rachel (December 24, 2009). "Johnny Depp explains how he picked his poison with the Mad Hatter". Los Angeles Times. Tribune Company. Archived from the original on November 15, 2010. Retrieved 24 December 2009.
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