Learning objectives: Reading this article will reinforce the reader's knowledge of the definition, pathophysiology, differential diagnosis, evaluation, and management of the most common of all the "eczemas," contact dermatitis, which can have an allergic and/or an irritant pathogenesis.
Data sources: Relevant articles and current texts on contact dermatitis were referenced and reviewed. The personal experiences of the authors in an Environmental Medicine Clinic, their private practices, and their teaching of residents and other physicians were evaluated. A MEDLINE database using subject keywords was searched from 1986 to date.
Study selection: Book chapters, pertinent articles, data source abstracts, guidelines for the management of contact dermatitis set by the American Academy of Dermatology, and the American Contact Dermatitis Society were critiqued.
Results: The recent elucidation of the pathoimmunology of contact dermatitis is concisely reviewed, highlighting its clinical implications. The protean clinical presentations of contact dermatitis, both "allergic" and "irritant" type are cited. The signs and symptoms warranting the search for a contactant are outlined. The most likely regional contactants are listed, but the need to reference a more complete textbook is often required. That patch testing is the gold standard to identify an allergenic agent causing allergic contact dermatitis is stressed. While the "who" and "when" to patch test is amply described, a cookbook "how" to patch test has been omitted in order to emphasize the importance of "hands on" experience for such testing. The advantages and limitations of the commercially available standard patch tests (Hermal, and T.R.U.E.) are described, plus the sources for "nonstandard" patch tests is made available. Therapeutic modalities, topical and systemic, for management of the uncomfortable patient are outlined.
Conclusion: The physician who manages a patient with an "eczematous" rash must be aware of the complete differential diagnosis of that clinical presentation. Suspicion that a "contactant" is the cause must have high priority, especially when the rash is persistent, and fails to respond to "appropriate" therapy. The value of a skin biopsy is limited to confirming its eczematous (spongiotic) nature and ruling out other diseases. Appreciating the paradox of patch testing, namely the deceptive simplicity of application versus the required expertise for interpretation and recognition of clinical significance, is the key to the proper management of the patient with contact dermatitis.