ESSENTIALS OF DIAGNOSIS
Erythema and edema, with pruritus, vesicles, bullae, weeping, or crusting.
Irritant contact dermatitis: occurs only in area of direct contact with irritant.
Allergic contact dermatitis: extends beyond area of direct contact with allergen; positive patch test.
Contact dermatitis (irritant or allergic) is an acute or chronic dermatitis that results from direct skin contact with chemicals or allergens. Eighty percent of cases are due to excessive exposure to or additive effects of universal irritants (eg, soaps, detergents, organic solvents) and are called irritant contact dermatitis. The most common causes of allergic contact dermatitis are poison ivy or poison oak, topically applied antimicrobials (especially bacitracin and neomycin), anesthetics (benzocaine), preservatives, jewelry (nickel), rubber, essential oils, propolis (from bees), vitamin E, and adhesive tape. Occupational exposure is an important cause of allergic contact dermatitis.
1. Allergic contact dermatitis
The acute phase is characterized by intense pruritus, tiny vesicles, and weepy and crusted lesions (Figure 6–27). The lesions, distributed on exposed parts or in unusual asymmetric patterns, consist of erythematous macules, papules, and vesicles and may occur beyond the contact area, distinguishing it from irritant dermatitis. The affected area may also be edematous and warm with honey-colored crusting, simulating—and at times complicated by—bacterial or viral infection (eFigure 6–86). The pattern of the eruption may be diagnostic (eg, typical linear streaked vesicles on the extremities in poison oak or ivy dermatitis) (eFigure 6–88) (eFigure 6–87), (eFigure 6–48). The location will often suggest the cause: scalp involvement suggests hair dyes or shampoos; face involvement suggests creams, cosmetics, soaps, shaving materials, nail polish; and neck involvement suggests jewelry, hair dyes. Reactions may not develop for 48–72 hours after exposure.
Allergic contact dermatitis to Neosporin. (Used, with permission, from Lindy Fox, MD.)
Contact dermatitis with linear pattern due to poison ivy. (Used, with permission, from TG Berger, MD, Dept Dermatology, UCSF.)
Poison oak. Note the linear streaky distribution of lesions. (Used, with permission, from S Goldstein, MD.)
Allergic contact dermatitis to an adhesive dressing in patient with darker skin. Key features are erythematous papules with impetigo-like honey-colored crusting. (Used, with permission, from Kanade Shinkai, MD.)
2. Irritant contact dermatitis
The rash is erythematous and scaly (but less likely vesicular) and occurs only in the direct sites of contact with the irritant. ...