Pitfalls in patch testing.

Allergic contact dermatitis is a common skin disease affecting both genders and individuals of any age. The patch test is the only useful in vivo method for the etiological diagnosis of allergic contact dermatitis. It is an apparently simple technique, but pitfalls may be encountered. False-positive and false-negative reactions are the most common. Times of occlusion and of reading may influence the result. Some difficulties are encountered in patients with active dermatitis or under immunosuppressive therapy, and climate conditions may interfere with the procedure. In addition, difficulties may be encountered in performing the patch test on dark-skinned patients, and patch testing in children may give some misconception due to the fact that the technique has been optimized in adults. A validated standard for readings and the interpretation of the patch test result is a recommended goa