Epikutantests

Epikutantests, also known as patch tests, are a diagnostic method in dermatology used to identify substances that cause allergic contact dermatitis. They help distinguish allergic reactions from irritant dermatitis and guide avoidance strategies.

In the procedure, small amounts of standardized allergens are applied to the back, usually in small chambers or patches, on a suitable vehicle such as petrolatum or water. The patches are left in place for about 48 hours, after which the test sites are removed and the skin is examined. Readings are typically performed at 48 hours and again around 96 hours; some centers perform a third late reading to detect delayed reactions. Reactions are interpreted using a standardized grading system and recorded as negative, doubtful, or positive with varying degrees of strength.

Results are correlated with the patient’s exposure history to determine the relevance of each positive reaction. A positive test indicates sensitization to a specific allergen, and clinically relevant positives are used to advise avoidance. Common allergen categories include metals (notably nickel), fragrances, preservatives, rubber additives, dyes, cosmetics, and contact allergens found in adhesives and topical medications. Standardized baseline series and country- or region-specific allergen panels are used, sometimes supplemented by user- or product-specific testing.

Limitations include the potential for irritant reactions to mimic positives, false negatives due to recent steroid use or immunosuppression, and variability in exposure history. Patch testing requires careful technique and interpretation by trained clinicians to determine relevance and to devise effective avoidance strategies.