ABSTRACT
Patch testing is a standardized diagnostic test routinely applied in clinical practice as the most important investigative method for studying delayed contact hypersensitivity (CHS). Properly performed and correctly interpreted patch testing represents the chief diagnostic method to confi rm allergic contact dermatitis. (ACD) A detailed clinical history complements, but does not replace the patch test in diagnosing ACD. Properly interpreted, patch test reactions are acceptable as “scientifi c proof” of the cause of dermatitis. It may be considered as one of the most direct of all methods of medical testing, as it employs the agent that causes the disease; it applies that agent to the target organ, and it locally reproduces the pathogenic mechanisms and morphological changes of the disease itself. The procedure involves the epicutaneous application, under controlled conditions, of a specifi c substance (allergen) that should induce a cutaneous infl ammatory reaction in the susceptible (sensitized) person; while causing no reaction in a non-sensitized person. The local reaction, reproducing the dermatitis “in miniature”, provides a visible representation of the subject’s general ability to react to the substance. Patch testing is very well tolerated, with very rare reports of systemic reactions.
