Patch Testing Guidelines for Allergic Contact Dermatitis

Target Audience: Dermatologists, allergists, primary care providers

Background and Objective

Allergic contact dermatitis, a cutaneous inflammatory process, is responsible for considerable morbidity and a common cause of occupation-related skin disease. Patch testing is used to diagnose the problem and identify responsible agents. Experts convened by the European Society of Contact Dermatitis developed guidelines regarding the use of this important diagnostic tool.

Key Points

• Patch testing is indicated when contact allergy is a consideration. It may also be useful in: 1) resistant cases of atopic, stasis, or seborrheic dermatitis with a possible superimposed contact allergy; 2) inflammatory disorders of mucous membranes; 3) when reactions to implants are suspected; and 4) some cases of erythema multiforme, lichen planus, psoriasis, and granulomatous reactions.

• When interpretation might be difficult (e.g., in patients taking immunosuppressive medications, when the dermatitis involves skin sites chosen for patch test application, or when patch test sites have recently been exposed to topical steroids or ultraviolet radiation) postponing patch testing might be prudent. Oral antihistamine use and topical steroids at other than the patch test sites are not a contraindication.

• In patients with immunosuppressive diseases or in whom withdrawal of immunosuppressive medications is impossible, patch testing can be performed, although test sensitivity may be reduced.

• Adequate evaluation of patch tests requires at least two readings — at days 2 to 4 and around day 7.

• Evaluation of specific products suspected of causing contact allergy can be performed with a repeated open application test: The agent is applied twice daily for up to 2 weeks on the flexural surface of the forearm near the antecubital fossa and the site watched for eczematous response.

• The frequency of positive patch test responses is often similar in patients with atopic dermatitis and the general population. Age is no contraindication to patch testing: Adults and children have similar likelihood of allergic contact dermatitis.

• Patch testing is generally very safe. Potential adverse effects include irritant reactions, sensitization to chemicals, pigmentary changes, flare of dermatitis in other body areas, and persistent reactions. Scarring and necrosis are extremely unlikely but have been described.