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EC number: 200-543-5
CAS number: 62-56-6
- van der Leun et al. 1977: Photocontact dermatitis was developed on
skin areas exposed to light by a 51-year old man three weeks after he
started working at a copying machine. The photopatch test produced
reactions to thiourea. The photosensitivity persisted although further
contact with the copy paper was avoided.
- van der Leun et al. 1977: A 40-year-old black-skinned architect
suffered from dermatitis on the hands and face. A marked increase in
photosensitivity in the UVB range was diagnosed (no further details). A
patch test revealed severe contact allergy to thiourea.
- Nurse 1980: A 41-year-old man developed dermatitis on the backs of his
hands about one year after getting in contact with copy paper. The
condition spread to the palms of the hands and finally also to the feet.
Sunlight aggravated the condition of the hands. The patch test revealed
reactions to exposed and unexposed copy paper, to a diazo compound
(“Diazo 580”) contained in the paper and to a 1 % aqueous thiourea
- Kellett et al. 1984: Dermatitis developed on the face, neck, arms and
hands of a 24-year-old man who had contact with diazo copy papers at
work. The patch test revealed reactions to thiourea (1 % in petrolatum
and 0.01 % in water) and to exposed and unexposed diazo copy paper from
the workplace. Increased sensitivity to UV light was not detected.
- Dooms-Goossens et al. 1987: A 40-year-old technical draughtsman who
worked with blueprints by scratching printed lines off the paper,
developed in the course of eight years a work-related skin disease.
Dermatitis developed first in the middle of his face and in the perioral
region and later spread to his forehead, neck and hands. Increased
photosensitivity developed, first after exposure to sunlight, later also
on exposure to neon light. Tests revealed increased sensitivity to UVA
light and to visible light (400 nm). This sensitivity regressed if the
patient was not at his workplace for weeks or months. Neither psoralen
UVA treatment nor the intake of beta-carotene prevented a relapse after
the man returned to his job. The patch test produced reactions to
thiourea (0.5 %, 1 %, 2 % and 5 % in petrolatum and 5 % in water), but
not to exposed or unexposed blueprints or paper scrapings from the
workplace of the patient. In the photopatch test more pronounced
allergic reactions to thiourea and to the paper scrapings were detected.
According to information from the manufacturer, the thiourea
concentration in the paper was about 0.04 mg/cm2, about a tenth of the
concentration of the 2 % thiourea preparation in petrolatum used in the
patch test. This could explain why the paper scrapings produced a
reaction only in the photopatch test and not in the test without light,
as radiation increased this patient's sensitivity to thiourea. The
facial dermatitis of the patient was explained by paper scrapings flying
about during the correction work, in other words by airborne contact
with the allergen
- Dooms-Goossens et al. 1988: A 24-year-old woman cleaning silverware
developed dermatitis on the tips of her fingers which, in the course of
several months, spread to her arms and face. The primary location of the
dermatitis was exactly the area of contact with the silver polish. Sun
exposure to the skin worsened the condition. The patch test revealed
contact allergy to thiourea (tests with 0.5 % in petrolatum and 5 % in
water) which was contained in the silver polish used at the workplace.
The patch test with thiourea (0.5 % in petrolatum) and exposure to light
produced a stronger reaction than without exposure to light
- Niinimäki 1989: A 36-year-old plumber suffered from dermatitis on the
ulnar side of the left hand which had direct contact with copy paper
during drawing and correcting. The dermatitis spread to the arms and
upper body. The photopatch test (UVA light, 5 J/cm2) produced a reaction
to 0.1 % thiourea (vehicle not specified), while the patch test without
exposure to light yielded negative results. The copy paper used by the
man at work contained less than 1 % thiourea. The skin reactions ceased
after the man changed his workplace
- Niinimäki 1989: A 40-year-old building contractor developed dermatitis
mainly on the backs of the hands; in the course of several months it
spread to his flanks and legs and became more severe on exposure to
sunlight. In the photopatch test, photocontact allergy to thiourea was
detected; the patch test without exposure to light yielded negative
results. At work the patient had frequent contact with copy paper which,
according to information from the manufacturer, was treated with a
solution containing 4–5 % thiourea
- Pasche-Koo and Grosshans 1991: A 39-year-old man who had daily contact
with diazo copy paper at work developed dermatitis on his hands,
forearms and face. In the patch test, contact allergy to thiourea was
detected but no other allergies. UV-sensitivity was normal. After the
man changed to another workplace without contact with diazo copy paper,
he suffered no further skin reactions
- Torres et al. 1992: A 44-year-old designer from an architect's office
in which diazo copy paper impregnated with a solution containing 5 %
thiourea was used developed contact allergy to thiourea. At first this
was clinically manifested as dermatitis on the hands, later also as
facial dermatitis, particularly in the periorbital region, as a result
of transferring the allergen with the hands. The patch test with 0.1 %
thiourea in petrolatum revealed a marked allergic reaction, the
photopatch test with the same preparation an even more severe reaction.
In the patch test the patient also produced allergic reactions to
dimethylthiourea, exposed and unexposed diazo copy paper from the
workplace and to hydroxylammonium chloride and sulfate. All three
chemicals were contained in the paper.
- Geier and Fuchs 1993: A 29-year-old construction engineer worked for
two years with diazo copy paper (blue prints) and then developed
work-related dermatitis with small blisters on his hands and sometimes
eczematous changes in the periorbital region. In the patch test, contact
allergy to a diazonium compound from the blue prints and to thiourea,
with which the paper was impregnated, was detected. A thiourea
concentration of 0.1 % in petrolatum was used for testing.
- Bartels and Schauder 1994: In a 45-year-old telecommunications
engineer who was employed mainly in system planning and had contact with
diazo copy paper, dermatitis on the back of the hands that had existed
for five years spread to areas exposed to light (face, neck). Exposure
to sunlight made the condition of the skin worse. At first the results
of the patch test were seen as an allergic reaction to the diazo copy
paper used at work; three months later, however, the allergic reaction
could not be reproduced in the control photopatch test without exposure
to light. However, in the test areas exposed to light (UVA light, 3.3
J/cm2) reactions occurred against diazo copy paper containing thiourea
and against thiourea (0.1 % in petrolatum). The patient was found to
have increased sensitivity to UVA and UVB, which had not returned to
normal even 294 days after ending contact with the diazo copy paper
containing thiourea. The unusual thing about this case is that the
sensitivity to UV light increased for more than 30 days after the end of
exposure to thiourea. The authors do not comment on other
photosensitizers with which the patient may have had contact.
- van Gerwen et al. 1996: A 37-year-old man who copied building plans
using the diazo procedure at work and suffered from work-related
dermatitis with small blisters on the hands produced a reaction to
thiourea in the photopatch test. Data for the test concentration, for UV
sensitivity and for the further course of the disease are lacking.
- Roberts and Hanifin 1980: Of seven patients with known contact allergy
to ethyl butyl thiourea, one also reacted in the patch test to 0.063 M
thiourea in petrolatum.
- Hölzle 1991: Thiourea (0.1 % in petrolatum) was tested between 1985
and 1990 in 45 dermatological centres in Austria, Germany and
Switzerland using the photopatch test. How many of the 1129 patients
were tested with thiourea, was not specified. Phototoxic reactions were
observed in 0.18 % of those tested, non-classifiable photoreactions in
0.55 % and a photoallergic reaction in none of the patients. Contact
allergic reactions occurred in 0.92 % of those tested. No information is
given on the clinical relevance of these reactions.
Relative to the number of persons exposed to thiourea, for example
through contact with diazo copy paper, the number of reported contact
and photocontact allergies to thiourea is small. In addition it is often
not clear whether or not the patient was exposed to thiourea as such,
thiourea derivatives or additional compounds in a mixtures. The MAK
Komission concluded in 2000 that "In view of the usually grave
consequences for those affected, contact or photocontact allergy to
thiourea, in particular with the development of a persistent reaction to
light, thiourea has nevertheless been designated with “Sh” and “SP” (for
substances where there is a danger of sensitization of the skin and of
photocontact sensitization)." However, this does not justify a
classification of thiourea as skin sensitizer under CLP.
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