Allergic contact dermatitis
The term “contact dermatitis” describes an inflammation of the skin caused by contact with external agents. Allergic contact dermatitis is a delayed-type hypersensitivity reaction due to the contact with a chemical to which the individual has previously been sensitised. Possible allergens are found in jewellery, personal care products, topical medications, plants and work-related materials. Usually, the eczematous reaction develops within 24 to 72 hours after contact with the causative chemical in a sensitised individual.
Clinical picture: An acute eczematous eruption may present with erythema, oedema, papules, vesiculation or bullae, displaying a polymorphic pattern. Not all the above-mentioned symptoms are necessarily manifested. The lesions are often accompanied by itching, burning or stinging. Chronic eczema is characterised by lichenification, scaling and possibly fissures, displaying a rather monomorphic pattern. Itching, burning and stinging may occur to a lesser extent than in acute eczema.
Distribution: The reaction is localised to the area of skin that comes into contact with the allergen. Patchy or diffuse lesions may also be seen. Systemic exposure to an allergen by oral or intravenous administration may lead to a diffuse dermatitis. Airborne allergens may produce lesions in the exposed portions of the skin, leading to an airborne contact dermatitis.
Diagnosis: The diagnosis is based on the patient history, clinical examination and patch testing.
Differential diagnoses: Other forms of dermatitis such as irritant contact dermatitis, atopic dermatitis, stasis dermatitis, asteatotic eczema, idiopathic dyshidrotic eczema and seborrhoeic dermatitis have to be taken into account. Depending on the localisation of the lesions, non-eczematous dermatoses such as erysipelas, rosacea (if the face is affected), palmoplantar psoriasis and dyshidrotic tinea manuum also have to be excluded. When there is widespread disease with diffuse distribution, Sézary syndrome and pityriasis rubra pilaris are possible differential diagnoses too.