Allergic contact dermatitis is the clinical expression of contact allergy. Contact allergy is an altered immune status of an individual induced by a particular sensitizing substance, a contact allergen. This involves a clinically unapparent sensitisation phase, also called the induction phase, resulting in the expansion of a clone of allergen-specific T cells. At this point, an individual is immunologically sensitised. Upon re-exposure with the same, or a cross-reacting, allergen/antigen, the elicitation phase is triggered, leading to specific T cell activation with clinically visible disease. In this guideline, the term contact allergy is used synonymously with contact sensitivity. The substances inducing contact allergy are reactive chemicals, usually with a molecular weight of <500 Da, but exceptionally in the range of 500–1000 Da. These substances are generally not antigenic by themselves, but only after protein binding, and are also referred to as haptens ((citation guideline, link – see above – to guideline)).”
Contact allergens for Allergic contact dermatitis
Common contact allergens are metals (nickel, chromium, cobalt, gold), fragrances (perfume chemicals), colophony resin, rubber chemicals, topical drugs (neomycin, corticosteroids), preservatives, plastic chemicals (acrylates, epoxy resins), dyes, formaldehyde, plants etc. In a patient with an established contact allergy, the interval between skin contact and the following eruption of dermatitis is longer than in cases of antibody-mediated allergies, viz. a matter of hours/days (delayed allergy). This efferent link involves aggregation of specific T lymphocytes at the site of cutaneous exposure to the antigen and release of biologically active cytokines resulting in clinical disease. An acquired contact allergy cannot be obliterated by treatment but is persistent for many years. If it possible to avoid contact with the allergen, dermatitis may, however, stay in remission. In principle, individuals are allergic to one chemical only – the allergy is antigen specific – but cross-sensitivity may be present: the patient may react with eczema to a chemically similar substance even if it is met in quite another product. Example: the patient may become sensitised to p-phenylenediamine in a hair colouring preparation but later flare up with eczema from p-aminobenzoic acid in a sunscreen.
Testing for Allergic contact dermatitis
Contact allergy is demonstrated through patch testing by a dermatologist. Small amounts of standardised and other suspected allergens are applied with an adhesive on the skin of the back for 48 hours. A positive test shows up as miniature eczema during the following few days. It is important to carefully consider the relevance of all positive patch tests since some of them may constitute immunological residues from eczematous episodes earlier in life. Treating Allergic contact dermatitis The main treatment for allergic contact dermatitis is by topical corticosteroids, often supplemented by moisturising creams, sometimes even ultraviolet radiation. In order to prevent a recurrence, it is necessary for the patient to avoid further contact with the allergen. Other types of contact dermatitis p Irritant contact dermatitis p Photocontact dermatitis p Contact urticaria
Treating Allergic contact dermatitis
The main treatment for allergic contact dermatitis is by topical corticosteroids, often supplemented by moisturising creams, sometimes even ultraviolet radiation. In order to prevent a recurrence, it is necessary for the patient to avoid further contact with the allergen.