Allergic skin disease
Atopic Dermatitis or eczema
The dry, scaling itchy rash that characterises eczema often occurs behind the knees, in fold of the elbow, or around the eyes. This can occur with other allergies and IgE sensitisation (especially in children) or alone.
Diagnosis of allergen sensitisation may help as avoidance of allergens such as foods or dust mites is helpful.
Some forms of dermatitis are due to contact- for example, with metals- or irritants. These have a different immunological basis to IgE mediated allergy and can be detected by patch tests where a test solution is applied to the skin for 48 hours or more to cause a delayed skin reaction.
Otherwise management is with moisturising creams and ointments, topical steroids or other anti-inflammatory medicine. Often a dermatology opinion is helpful.
Anti-histamines are of little help for the itching of eczema.
Urticaria occurs as outbreaks of raised red itchy lumps similar to those after a nettle sting. It can be acute and disappear rapidly or persist for over 6 weeks (chronic urticaria). Chronic urticaria can be debilitating. It may have a physical cause such as heat, cold, pressure or exercise, but is rarely due to a specific allergic trigger through IgE sensitisation. Exhaustive searches for a cause or strict exclusion diets are seldom helpful.
Management is with high doses of antihistamines or other agents with anti-histaminic properties. Occasionally anti-inflammatory agents such as cyclosporine A are used but this should be in consultation with a dermatologist.