Snapshot A 3-year-old boy presents to his pediatrician's for a rash on his left lower leg. He had been playing in a wooded area yesterday. He reported a very itchy rash on his left lower leg since this morning. On exam, there are erythematous papules and vesicles in a linear pattern, as though he had brushed something. He is given topical corticosteroids and reassurance. Introduction Clinical definition erythematous and pruritic rash caused by cutaneous exposure to allergens most common form of contact dermatitis irritants often involves hands often from occupational exposures Epidemiology prevalence 15-20% demographics female > male risk factors exposure to potential allergens or irritants occupations with higher risk of contact dermatitis healthcare food production cosmetics Etiology most common allergens include poison ivy poison oak nickel most common irritants include chemicals alcohol Pathogenesis allergic contact dermatitis immunologic reaction to allergen causing type IV hypersensitivity reaction delayed T-cell mediated reaction activation of Th1 cells memory CD4+ cells are created and dermatitis develops upon re-exposure or cross-reaction irritant contact dermatitis nonimmunologic reaction to substance that causes direct damage to the skin release of inflammatory cytokines activated by non-immune pathways Prognosis typically resolves with treatment Presentation Symptoms presents 12-48 hours after exposure to allergen pruritic burning or stinging Physical exam linear or geometric rash, corresponding to topical exposure, composed of papules and vesicles can progress to blisters and bullae for example, patients allergic to the adhesive in a bandaid will present with a square or rectangular-shaped rash eczematous rash lichenification fissuring scaling Studies Labs none Patch testing to identify potential allergens help prevent future exposures Histology spongiosis (epidermal intercellular edema) Differential Atopic dermatitis Treatment Conservative skin moisturizer indication decrease irritation in nonimmunologic contact dermatitis Medical topical corticosteroids indication localized or mild-to-moderate disease first-line therapy systemic corticosteroids indications widespread or severe disease disease that involves mucosa Comlications Secondary bacterial infection