Contact dermatitis

Overview & Definition

Picture the eight-year-old who returns to clinic with the same angry, weeping band of eczema around her navel that cleared with steroid last month and came back the day she wore her favourite jeans with the metal button. Her atopic eczema elsewhere is well controlled, yet this one patch refuses to settle. That pattern — a same-site, recurrent, anatomically-clued eruption — is the fingerprint of allergic contact dermatitis, and it is the scenario every general paediatrician must learn to spot. [8]

Contact dermatitis is an eczematous skin inflammation arising from direct skin contact with an exogenous agent. It is divided into irritant contact dermatitis, caused by the direct cytotoxic effect of a chemical or physical agent on the skin cells, and allergic contact dermatitis, a cell-mediated delayed type IV hypersensitivity reaction to a specific allergen. A third, overlapping pattern is photocontact dermatitis, in which a topical or systemic agent becomes allergenic or irritant only in the presence of ultraviolet light. In children, irritant disease is far more common than allergic disease, but the latter is increasingly recognised as patch testing becomes more available. [11] [10]

Three ideas anchor the whole topic. First, the morphology of contact dermatitis is eczematous — erythema, vesicles, weeping, scaling and eventually lichenification — so it mimics and often coexists with atopic eczema, which is the commonest source of diagnostic error. Second, the distribution is the key to the cause: a sharply demarcated eruption in the shape of the offending object or at the site of contact points straight to a contactant, whether irritant or allergic. Third, the distinction between irritant and allergic disease matters because management differs — both need removal of the cause and barrier repair, but only allergic disease benefits from patch testing, allergen identification and long-term avoidance counselling. [8] [9]