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Contact Dermatitis

»	Name the two pathogenic types of contact dermatitis.
»	Name the two subtypes of irritant contact dermatitis, and describe them.
»	Explain the pathogenesis of allergic contact dermatitis (ACD).
»	Can urticarial reactions occur from contact with a substance?
»	Why is the distribution of a contact dermatitis rash important?
»	List three common misperceptions regarding the location of a contact dermatitis.
»	How is patch testing done?
»	What substances are tested in the standard “screening” patch test?
»	An astute physician should not need to patch test. Right?
»	What is a repeated open application test (ROAT)?
»	What is the differential diagnosis of contact dermatitis?
»	Which is the most common allergen on the standard tray?
»	Is nickel the most common allergen overall?
»	If a change in a skin care product does not lead to clearing of a patient’s rash, does this mean that the original product was not the culprit?
»	How is contact dermatitis managed?

What is a repeated open application test (ROAT)?

Fig. 9.5 Positive ROAT test from a moisturizing cream.

The ROAT, or usage test, is used when patch testing is negative, and yet there remains a strong clinical suspicion for ACD. Remember, patch testing is a onetime occlusive test that does not always duplicate low-level chronic daily exposure. With the ROAT, patients apply the suspected product to a quartersized area on the forearm twice a day for 1 week. If the patient is allergic, a localized dermatitis will occur, confirming the suspected allergy (Fig. 9-5).