Provocation factors in atopic dermatitis
A number of different triggers of atopic dermatitis are well established. The relative
importance of these triggers will depend on whether the patient first sees an Allergist
or a Dermatologist.
The Eczema – Food Allergy Story
The role of food allergy in atopic dermatitis has been the source of more controversy
than perhaps any other skin disorder. The disagreement oftentimes is one of semantics.
The fact that some patients with atopic dermatitis respond adversely to some foods
at some time in the history of their disease cannot be denied. The fact that exacerbations
of atopic dermatitis can be caused by multiple and varied "triggers" confounds
the objective evaluation of any single trigger. One should not allow rationality
to succumb to emotions.
Positive skin prick test to foods only mirrors serum food specific IgE responses
to food antigen, it does not equal clinical food allergy. Hugh Sampson demonstrated
this when he demonstrated that, in his select population, only one-third of patients
with positive skin prick test result correlated with positive food challenge result.
Positive skin prick test or RAST have been reported in 51% to 96% of patients with
AD. Unfortunately, the positive predictive value of skin prick tests is less than
50%, but the negative predictive value is more than 90%. So a negative skin prick
test almost certainly excludes a food allergy.
Double-blind placebo-controlled food challenges (DBPCFCs) must be considered the
most reliable technique for confirming the diagnosis of food allergy (the "gold
From many studies utilizing DBPCFCs, 33% to 66% of patients with AD tested developed
a reaction when challenged. DBPCFC has been reported to produce skin reactions in
84% to 96% of patients tested. These reactions, however, develop within minutes
up to 2 hours after challenge and last only 30 to 120 minutes. It is believed that
this reaction causes histamine release from mast cells, which is the stimulus for
the itch in Eczema.
In Dr Hugh Sampsons (tertiary) hospital referral population, 80% of the children
evaluated were found to be food allergic. It is also found in several paediatric
studies, that the more severe the atopic dermatitis, the more likely food will be
a clinically relevant trigger.
Fortunately, food hypersensitivity in young patients is not always a life-long affliction.
One study reported that food sensitivity persisted in 67% of children 7 to 16 years
of age with severe AD and was always associated with aeroallergen sensitivity. Hugh
Sampson reports that the development of tolerance to peanuts, nuts, and seafood
almost never occurs, whereas children sensitive to soy, milk, eggs, and wheat frequently
outgrew their clinical reactivity after several years of allergen avoidance.
Based on all the studies it can be concluded that in patients with persistent, generalized,
moderately severe to severe AD, food allergy should always be excluded.
Irritant triggers in AD
The most consistent perturbations of atopic dermatitis are irritants. The skin response
to irritants is increased in atopic individuals with or without apparent dermatitis.
Occupational substances have particular clinical and social
Intolerance to wool is in part based on its irritating effect on the skin (other
part related to the dust mites which it harbours).
Cigarette smoke may also elicit irritating eczema on the eyelids in atopic dermatitis.
It is speculated that an altered composition of the epidermal lipids, an enhanced
release of histamine, or a latent, subclinical inflammatory reaction in the skin
may play a role in the enhanced vulnerability of the atopic skin.
Both systemic and local infections can trigger the eczematous response in atopic
dermatitis. Staphylococcus aureus has been studied extensively as a possible
trigger factor as it is detected in the skin in more than 90% of all atopic dermatitis
patients. Exotoxins are detectable in two thirds of all cultures containing
which have been generated from skin swabs in AD. They may function as superantigens,
which are capable of stimulating the release of potent inflammatory agents.
It is well established, in clinical experience, that atopic dermatitis can be improved,
in many cases by systemic antibiotics. This may be associated with the reduction
of superantigens on the skin.
In addition to s. aureus, the saprophyte Pityrosporum ovale
is thought to elicit a specific immune response and thus provoke eczema
on the face and neck of atopic dermatitis patients.
Environmental and contact allergen
Hypersensitivity to house dust mite antigen is found in 5% of all people in Western
nations whereas it is found in up to 90% of adolescents or adults suffering from
atopic eczema. Exacerbations of atopic dermatitis caused by dust mites are presumed
to be related to both inhalation and skin contact. Several clinical studies have
reported improvement of the skin condition after a reduction in the level of house
In addition to mites, sensitisation to pollen or animal dander may be associated
with eczematous skin reactions. Therefore, contact with animals should be avoided
even if the patients do not suffer from respiratory symptoms.
Most studies indicate that the frequency of sensitisation to contact allergens in
ingredients of common preparations (e.g., vehicles, preservatives, fragrances, antibiotics,
steroids) appear to be higher than normal. Thus, classical
should not be neglected in patients with atopic dermatitis
because it may reveal important cofactors in the development of eczematous skin
lesions in these patients.
Hormonal and emotional factors
Fluctuations in severity of atopic dermatitis are frequently observed in women.
This points to hormonal influences with menstruation, pregnancy, birth and menopause
as possible trigger factors.
Many studies emphasize the importance of psychological factors, such as personality
traits or psychological stress, in the worsening and maintenance of skin symptoms.
Stressful life events may be associated with an increas in itching which leads to
scratching and, by this mechanism, to a deterioration of the skin condition. Neuropeptides
and increased number of nerve fibres, which have close contact with mast cells may
be possible links between the nervous system and the skin in atopic dermatitis.
Diagnosis of AD
Simplified Diagnostic criteria of Atopic Dermatitis
(According to the UK Working Partys diagnostic criteria
for Atopic Dermatitis)