Epidermal damage induced by irritants in man: a light and electron microscopic study

Irritant contact dermatitis may be induced by many chemicals and has a far greater incidence than allergic contact dermatitis. Despite this, it receives relatively little attention and its pathogenesis remains poorly understood. To gain a greater understanding of the interaction of irritants with the skin, we investigated the histopathological changes resulting from the topical application of a series of structurally unrelated irritants. Human volunteers were patch-tested with appropriate concentrations of nonanoic acid, sodium lauryl sulphate, dithranol, benzalkonium chloride, croton oil, and propylene glycol, which produced generally mild to moderate responses. Biopsy specimens were taken after 48 h and examined by light and electron microscopy. Spongiosis and the infiltration of predominantly mononuclear cells were observed in the epidermis of the majority of biopsy specimens, and were particularly pronounced and extensive in croton oil reactions. In addition, several irritants induced distinct and characteristic patterns of keratinocyte damage. Nonanoic acid and sodium lauryl sulphate caused morphologic changes indicative of disturbances in keratinocyte metabolism and differentiation, giving rise to dyskeratosis and parakeratosis respectively, while dithranol induced marked swelling of keratinocytes in the upper epidermis. The results suggest that there is a diversity and specificity in the histopathology of irritant contact dermatitis, reflecting the different ways in which chemicals may interact with components of the skin.