Epicutaneous testing.

The patch test and chamber test are the ordinary methods for detecting delayed type contact allergies. The method, test substances and criteria of positive reactions are already well standardized. Open testing is also used for problematic chemicals such as strong topical medicaments, emulsifiers and propylene glycol. The many problems of standardization are still unresolved in photocutaneous testing. Some chemicals are applied to the skin without occlusion, though the chamber test or patch test methods are used with most of them. The composition of the vehicle and occlusion time vary greatly from one photosensitizing substance to another. A xenon arc is recommended for screening any photosensitizers but fluorescent black light tubes are sufficient for routine clinical use. Type I contact allergies are far more common than was previously believed, especially among people allergic to birch pollen. This type of reaction and other forms of contact urticaria can be examined using the scratch chamber or scarification chamber techniques as well as with an open test on diseased or scratched (scarified) skin.