»	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?

List three common misperceptions regarding the location of a contact dermatitis.

Fig. 9.3 Allergic contact dermatitis of the neck due to a nail polish transfer reaction.

Dermatitis has to be bilateral if the exposure is bilateral, that is, with a shoe or glove allergy. In most cases, contact reactions tend to be patchy and do not have the same intensity at all sites of exposure.
The rash of contact dermatitis occurs only at the site of maximal contact. Allergens can frequently be spread to distant sites of contact (Fig. 9-3), as when nail polish is transferred to the eyelid, inducing dermatitis when a sensitized patient rubs her eyelids with her fingernails.
Contact dermatitis does not affect the palms and soles because of their thick stratum corneum. Although it is true that other more sensitive areas such as the eyelids, face, and genitalia are more likely to be reactive, contact dermatitis definitely should be considered when dealing with an eczematous dermatitis of the palms or soles.