Contact allergy (allergic contact dermatitis)
General: An allergy is in a way a malfunction of the immune system through which antibodies or defence cells act against actually harmless foreign substances. There are different forms of allergies. They all have in common that the immune system must first “learn” the allergic reaction. This process is referred to as sensitisation phase. It goes normally unnoticed. Only after a new contact with the allergen, the allergic reaction develops. Consequently, there are no innate antibodies.
The immediate type allergy is caused by certain antibodies, namely immunoglobulins of Class E and is in most cases directed against exogenous proteins, eg in pollen, house dust, insect poison or foods. Classic diseases, which are an expression of an allergy of the immediate type, are hayfever (allergic rhinitis), allergic asthma bronchiale or in extreme cases the anaphylactic shock. Urticaria (nettle rash, itching hives) or gastro-intestinal disorders may likewise be caused by an immediate type allergy. As a rule, the disorders appear within minutes; the allergy form owes its name to this. The diagnosis of the immediate type allergy can include the determination of immunoglobulin E in blood, a prick test on the skin or also a provocation test. During a prick test, standardised allergen solutions are dropped onto the skin and then the skin is punctured with a small lancet, so that the allergen (as a rule a high molecular weight protein) can penetrate the upper dermal layer. After 15 minutes a reddening of the skin with a small urtica appears in the event of an allergy.
A completely different event underlies the contact allergy, which is covered in more detail in the following sections.
Contact allergy: The contact allergy is caused by specifically marked T-lymphocytes (a certain sort of immune-cells). Here it takes as a rule hours to days before an allergic reaction develops after the skin contact with the allergen; this is also why the contact allergy is referred to as “delayed type allergy”. The appertaining clinical picture is the allergic contact eczema. The eczema develops primarily in the contact area with the responsible allergen, but can also “spread”, ie disseminate to other skin areas.
It is assumed that approximately 20 to 25 % of the European population suffers from a contact allergy; this is hence a widely spread disease. Women are affected more frequently than men. The contact allergy lasts a lifetime and cannot be cured so far; there is no hypo-sensitisation for contact allergy – as opposed to immediate type allergy. The persons concerned can, therefore, only remain asymptomatic if they know their allergen and avoid contact.
The Information Network of Departments of Dermatology for recording and scientific analysis of contact allergies (IVDK) pursues the objective of identifying contact allergens and monitoring the contact allergy developments. IVDK records data on contact allergy from 56 clinical allergy departments in Germany, Austria and Switzerland. In the current IVDK data nickel is the by far most frequent contact allergen, followed by cobalt, balsam of Peru, fragrance mix, chromate and propolis.
Symptoms of a contact allergy: In the event of an allergen contact, the contact allergy results in an inflammation of the epidermis and the contiguous dermis, ie an allergic contact eczema with skin reddening (erythema), infiltration of the skin with inflammatory cells (papules, palpable infiltrate), vesicula, scaling and secondarily with weeping, erosions and / or encrustation. The cardinal symptom is itching.
If skin contact with the allergen persists over a longer period of time, a chronic contact eczema can develop with the following symptoms: swelling of the skin through migrated inflammatory cells, coarsening of the skin folds and thickening of the horny layer with coarse scaling and development of fissures.
Diagnosis: Since a contact allergy lasts a lifetime and cannot be removed, the persons concerned must know their allergen(s) because only by avoiding allergens can they remain symptom-free in the long run. The diagnosis is carried out by a medical specialist using the so-called patch test. The possible contact allergens are filled in standardised form (in petrolatum or in water) into small test chambers and applied with an adhesive tape onto the healthy skin in the upper part of the back. After 48 hours the test chambers are removed and the test fields are marked. The test is read out after removing the test adhesive tapes as well as at least one or two days later. In the event of a contact allergy, a small allergic contact eczema develops in the test field of the originally responsible allergen with reddening, papules and possibly vesiculas. The contact allergy reaction reaches its peak in most cases on day 3 or 4 after the application of the test adhesive tape (ie one to two days after the removal of the adhesive tape) and then disappears again.
As for every biological and / or diagnostic test, there are here also occasionally false positive reactions. For this reason the interpretation of the test result should always be carried out by a medical specialist or specially trained staff. The test can merely inform about whether the person concerned has a contact allergy. Whether this allergy is actually responsible for the skin lesion can only be assessed taking into account the clinical history (anamnesis).
Data from the allergy pass or patient information from the medical specialist: The contact allergies determined in the patch test should be documented in an allergy pass or patient information. If the contact allergen concerned is an ingredient of a cosmetic product, the persons concerned have the possibility to identify their allergen on the packages of the cosmetics which must list all ingredients. For many substances there are several different designations. In order to facilitate identification, the “International Nomenclature of Cosmetic Ingredients” (INCI), which is a European-wide standard, is used. This is why the INCI name should also be listed in the allergy pass or the patient information.
Management of the contact allergy: An allergic contact eczema can be easily treated, but the underlying allergy not (see above). Only by avoiding skin contact with the allergen can the recurrence of the eczema be avoided. In this connection it is necessary that the persons concerned are aware of their allergen and know where it can occur.
Source: Prof. Dr. med. Johannes Geier, Information Network of Departments of Dermatology for recording and scientific analysis of contact allergies (IVDK)