Allergic contact dermatitis: diagnosis and treatment
In allergic contact dermatitis, the skin is red and itchy in the place where it came into direct contact with the trigger ( allergen ). Initially, blisters appear , which may ooze and form scabs. Those affected also suffer from itching. Skin tests help with diagnosis , because an allergic rash cannot always be clearly recognized by its appearance.
How is allergic contact dermatitis diagnosed ?
In rare cases, the affected areas of the skin can even become inflamed – then medical treatment is absolutely necessary at the latest. After it is possible to avoid contact with the allergen , allergic contact dermatitis usually disappears slowly but surely. If it is a chronic skin manifestation, the redness disappears, the skin scales and thickens (chronic contact dermatitis). This problem can also turn into so-called chronic degenerative contact dermatitis, which is characterized by dry skin and significantly longer healing.
Finding out the medical history
Diagnosis begins with taking a detailed history. The doctor will ask the patient whether he (or his family) has ever had any allergies, what his occupation is, how he takes care of his skin, or whether he is taking any medications . It is quite possible that it is not an allergic contact dermatitis, but an irritant contact dermatitis that arose, for example, in response to a new detergent. Patients often suspect specific substances with which they have recently come into contact. In most cases, however, these are triggers with which the patient is in regular and long-term contact. If, after the initial diagnosis of allergic contact dermatitis, the rash appears again after further contact with the allergen, it is clear that the diagnosis was correct. Then there is nothing left to do but strictly avoid contact with the trigger to prevent another rash.
Epicutaneous test : a skin test to confirm the diagnosis
If allergic contact dermatitis is suspected, an allergy test is performed in so-called standard kits. The most common type of epicutaneous test is the closed (patch) test , where the doctor sticks patches containing allergens on the back. After 24, 48 or even 72 hours, it is checked if there is a visible skin reaction. If the reaction is unclear, another reading may follow 24 hours later. When performing epicutaneous tests, it is necessary to take into account in advance that allergens can cause unpleasant local reactions on small pieces of skin.
The second type of epicutaneous test is an open test , where the allergen is not stuck under the patch, but is applied to a certain area of the skin several times a day. This type of patch test is particularly useful for testing substances such as shower gels or disinfectants . The evaluation is carried out after 48 and 72 hours.
The third type of epicutaneous test is the photoepicutaneous test or photo patch test , which is used to diagnose photoallergic contact dermatitis (see also the article Allergy to the sun ). This appears in the case of the interaction of a photosensitizing substance and UV radiation . In this examination, the tested allergens are applied in the same way as in the classic patch test, but in two sets of allergens. One set is removed after 24 hours of exposure and the skin underneath is irradiated with UVA radiation, the other set remains glued and is removed only after 48 hours (without UVA exposure ). The doctor then compares the two sites: if an allergic reaction is observed in both sets, it is “classic” allergic contact dermatitis; if the reaction is observed only in the kit that has been irradiated with UVA radiation, it is photoallergic contact dermatitis. This is usually the result of the combined effect of a substance (e.g. skin cream containing an allergen) and UV radiation. Photoallergic contact dermatitis is therefore mainly visible in places exposed to light, but it can also spread to the surrounding area.
Your doctor will explain the risks and side effects of the test. A positive test result does not necessarily mean that it is actually an allergy.
How is allergic contact dermatitis treated?
The treatment of allergic contact dermatitis consists primarily of avoiding allergens, in the acute phase local treatment (creams, etc.) is also used. In any case, you should contact a dermatologist , who can arrange a more detailed explanation of the allergy – whether he makes the diagnosis himself or sends you for a special examination at an allergy clinic. In case of a positive test result, the allergen will be recorded in your allergy card.
Avoid allergens
The first step in the treatment of allergic contact dermatitis is advice on possible substances or products that contain the given allergen. The patient should of course avoid these products. Unfortunately, this is not always possible, especially if allergens are almost ubiquitous. In this case, efforts should be aimed at least at limiting contact with the allergen.
Creams, ointments, cortisone , etc.
Depending on the stage of the allergic skin change, medicines are applied to the skin (local treatment). If the eczema oozes, hydrophilic emulsions, creams or aqueous solutions are applied. If the skin is dry, a greasy ointment is applied. Corticosteroids (either applied to the skin or in the form of tablets, only in severe cases in the form of an infusion ) are used to keep the inflammation under control. The time that cortisone is applied to the skin is usually limited because the side effect is thinning of the skin. However, it is usually possible to restart the treatment after stopping it. If the rash shows signs of infection , antibiotic treatment may be necessary .
You should regularly use a moisturizing skin cream recommended by your doctor to gradually restore the skin and its natural barrier. In addition, preparations containing urea can be applied to the skin .
For the treatment of moderate to severe atopic eczema, so-called calcineurin inhibitors are sometimes used . These can be prescribed by a doctor in case of allergic contact dermatitis on the face, because the skin thins less after them than after cortisone creams.
In rare cases, immunosuppressants are used . Furthermore, therapy with ultraviolet light can have a supportive effect , especially in the case of the chronic variant.
Who can I contact?
Allergists diagnose and treat allergic contact dermatitis. However, the first step is usually a visit to a dermatologist, who will pronounce the expected diagnosis and at the same time rule out other skin diseases .
