Contact Hypersensitivity to Environmental Chemicals

Abstract

Allergic contact dermatitis has been defined in many ways: the classical statement in toxicology texts states that it occurs after multiple (rather than first) exposures, is immunologic (cell mediated), and that it can be reproduced by patch testing at low levels of antigen. In recent years this definition has proven inadequate and it has led to incorrect classification of several dermatitis producing chemicals. For this reason, an operational, rather than a purely mechanistic definition, has proven more useful. This operational definition includes not only patch test results, but verification (retesting) and provocative use tests, to rule out the Excited Skin Syndrome (see below).