Contact allergy and atopic dermatitis 
Review paper 
CONTACT ALLERGY AND "ATOPY PATCH TESTS" IN 
A TO PIC DERMATITIS 
B. Wilthrich 
ABSTRACT 
The prevalence of contact sensitization in atopic dermatitis (AD) patients varies considerably, in dependence of sex, age, 
occupation, the population tested, i.e. patients with a long history of the disease, the allergens used and the country. Because of 
the highly irritable atopic skin unspecific irritant reactions were seen in 24 % to 40 % of the AD patients. The chemicals most 
frequently involved in contact sensitation are nickel sulfate, potassium dichromate, cobalt chloride, neomycine and benzoyl 
peroxide. 
The prevalence of atopic patch tests with aeroallergens (housedust mites, pollens, animal danders and moulds) also v ary from 
few to 70 % ofthe various tested allergens and the different authors. These findings support the hypothesis that direct epidermal 
contact with aeroallergens may play a pathogenetic role in some patients with AD. 
Positive atopic patch tests to aeroallergens are not only present in patients with AD and positive specific prick tests or serum 
IgE (RAST) but they can also occur in presence of negative prick test reactions or negative specific IgE levels. Intemational 
recommendations for standardization and evaluation of atopy patch tests are urgently needed. 
KEYWORDS 
atopic dermatitis, contact allergy, atopy patch tests, aeroallergens 
PREV ALENCE OF CONT ACT ALLERGY 
Reports on the prevalence rate of contact sensitization in 
atopic dermatitis (AD) patients are contradictory. The 
80 
Intemational Contact Dermatitis Research Group (ICDRG) 
demonstrated that the incidence of contact allergy is similar 
in atopic, seborrhoic and nummular eczema (2). However, 
acta dermatovenerologica AP.A. Vol 2, 93 , No 3 
Contact allergy and atopic dermatitis 
Fig . 1 An irritant,follicular reaction to tocopheryl linoleate 
(an ingredient in cosmetics) in atopic dermatitis. 
Fig. 2 Positive atopy patch test reactions to housedust mites 
Dermatophagoides pteronyssinus ( 1) and farinae (2) at the 
lecture on48 hrs only onstripped ( l 2x) skin, but not on intact 
skin. Negative reactions to birch (3), grass pollen (4) and 
saline control (5 ). 
acta dermatovenerologica AP A. Vol 2, 93, No 3 81 
Contact allergy and atopic dermatizis 
the rate of sensitization is much Iess pronounced than in the 
group of patients with stasis dermatitis. There are many 
articles which show that patients with severe AD and with 
high IgE values ( > lQO U/ml ) display a decreased capacity 
to develop contact sensitivity as a consequence of an altered 
function of the cellular immunity (8, 11, 15). On the other 
hand, the irritant properties of the tested substances should 
not be understimated, especially when testing young children 
and patients with a widespread and long-Iasting dermatitis 
with a high irritable skin. Irritant reactions were seen in 24 % 
to 40 % of the AD patients and the list of substances eliciting 
irritant or follicular reactions (Fig. 1) is very wide and 
contains pharrnaceutical substances, vehicles and cosmetics, 
such as forrnaldehyde, fragrance-mix, carba-mix and 
propylenglycol, and environmental and professionalhaptens, 
such as rubber products and metals (5, 9, 10, 14). 
The distribution of the haptens that are most frequently 
involved in eliciting true positive patch test (PT) reactions in 
AD can also vary considerably, in dependence of sex, age, 
occupation, the population tested (i.e. patients with a Iong 
history of the disease ), the allergens used, and the country. 
Nevertheless, the chemicals most frequently involved are 
nickel sulfate, especially among women and younger atopics, 
potassiurn dichromate, cobalt chloride, neomycine and 
benzoyl peroxide (2, 3, 6, 9, 10, 12). 
On the other hand, the clinical relevance of such positive 
PT is often hard to verify. In a recent study it was shown that 
no differences concerning the occurence of positiveresponses 
existed in atopics with and without hand manifestation and 
that in only 3/136 patients the result of PTs did explain the 
occurrence ofhand eczema (4). 
In conclusion, despite standardization of PT methods and 
development of test materials and devices, i.e. with the 
TRUE test system, it remains difficult to distinguish between 
true allergic and irritant reactions in patients with irritable 
skin and to judge about the clinical relevance of such positive 
PTs. Therefore, epicutaneous patch testing in atopic dermatitis 
should only be performed by well trained and experienced 
physicians. 
"ATOPY PATCH TEST" 
WITH AEROALLERGENS 
Patients with AD, also without concomitant respiratory 
allergies, frequently show sensitization to aeroallergens of 
the immediate type in skin tests and/or in RAST (27, 28). The 
skin lesions, however, are clinically and histologically those 
of a subacute or chronic eczema with the features of a delayed 
type hypersensitivity reaction (1). Therefore, the immediate 
type reactions to inhalant were often regarded as an 
acta dermatovenero/ogica A.P.A. Vol 2, 93, No 3 
epiphenomenon without clinical significance for the atopic 
skin manifestation or as an indicator for a respiratory allergy 
of the airways. Nevertheless, some clinical observations of 
flares of AD in springtime by pollen exposures (AD as hay 
fever equivalent) or ofimprovements after allergen avoidance, 
such as house dust mites or chironomides infishfood, and IgE 
sensitization to therelevant allergens, stressed the pathogenetic 
significance of aeroallergens at least in a subgroup of AD 
patients (28). In thesecases it was assumed thathaematogenous 
skin contact after inhalation of inhalant allergens can elicit a 
flare-up of AD. 
Already 1945 it was shown that patch tests to human 
dander from the scalp of normal adults produced positive 
eczematous reactions in a high percent of patients with AD. 
Subsequently, severa! authors have reponed positive PT 
reactions of the delayed type to house dust mites, pollens, 
animal epithelia and mould extracts (1, 5, 7, 9, 10. 13, 14, 16, 
17, 19, 20, 21, 22, 24, 26) (Fig . 2). The frequency ofthese 
positive PT differs from few to 70 % percent for the various 
tested allergens and the different authors, supporting the 
hypothesis that direct epidermal contact with such 
aeroallergens may play a pathogenetic role in some patients 
with AD. It was subsequently shown that positive patch tests 
to aeroallergens are a specific feature of AD as they were not 
observed in atopic patients with rhinitis or asthma without 
eczema, also in the presence of a su-ong lgE sensitization to 
the tested allergens. Viceversa, there were no difference 
between patients with "pure" AD and those with associated 
respiratory allergies (5, 18). 
Originally, it was thought that "atopy patch tests" (APT) 
were present only in patients with AD and positive specific 
prick tests or serum IgE. Recent works show that positive 
APT also occur in presence of negative prick tests reactions 
or negative specific IgE levels (25). So far, there was no 
correlation between dust mite-specific lgE and PT reaction 
for dust mite antigens. Recently, it has been suggested that 
the results of APT and specific serum IgE could be used to 
divide AD patients into four distinct groups, each with its 
own particular clinical morphology, suggesting the 
heterogeneity of this disease (7). However, the existence of 
these four different subtypes must await further investigations. 
Parallel to these clinical findings , the mechanisms 
underlyingpositiveAPTin_patientswithADwereinvestigated 
by severa! groups. The presence of lgE on epide1mal 
Langerhans cells and the isolation of antigen-specific T cell 
clones from the test sites - as a link between specificlgE and 
cell-mediated immune response - is now seen asa possible 
pathogenetic mechanism in AD orat least acting in positive 
APT reactions (1, 20). 
Unfortunately, in contrast to classical PT for contact 
dermatitis, there have been umil now no international 
83 
Contact allergy and atopic dermatitis 
recommendations for standardization and evaluation of APT 
(18). In fact, there exist important differences between the 
different authors conceming the carrying-out of these APT: 
-conditions of application on the skin (intact, slightly abraded, 
stripped or scratched skin (Fig. 2), 
- site and size of the test area, 
- application period (24 or 48 hrs), 
- nature, origin and concentration of allergen extracts 
(Der pl/fl, Der pII/fll, body antigens, fecales, whole mite 
cultures a.o.; same or stronger concentration than prick test 
solutions etc ), 
- nature of vehicles used (glycerol, saline, vaseline), 
- patient selection, 
- classification of test reactions (grading, allergic or irritative 
reaction ?) . 
The editing of such recommendations could be the task of 
the European Society ofDermatology. 
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AUTHOR'S ADDRESS 
Brunello Wiithrich M.D., Professor ofDerrnatology and Allergology, Head Allergy Unit, Deparunent of Dermatology, 
University Hospital, Gloriastrasse 31 
CH-8091 Zurich, Switzerland 
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