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The histopathological features of allergic contact dermatitis were compared with those of irritant contact dermatitis in a group of 17 subjects. Each patient received simultaneous patch tests of a known allergen and a standardized irritant (benzalkonium chloride). The cellular changes occurring between 3 h and 7 days after patch test application were studied by light and electron microscopy and immunocytochemistry. No differences were observed between the induced allergic contact dermatitis (ACD) and the irritant contact dermatitis (ICD), either in the responding cell types or the sequence of cellular events. Both reactions showed a predominantly T lymphocyte infiltrate with no polymorphonuclear leukocyte involvement. Apposition of Langerhans cells to lymphocytes in the epidermis was seen in both types of response. Considerable variability in the intensity of reaction to irritant and allergen occurred within individuals. There was no statistically significant difference between the intensity of the reactions to the irritant and the allergen.

Compositae dermatitis is rare in childhood, with few cases documented in the literature. We report a 7-year-old boy who presented with a dermatitis mainly affecting his dominant hand. Patch testing revealed contact sensitivity to sesquiterpene lactone (SL) mix, and subsequent testing with Compositae oleoresins showed sensitivity to daisy, dandelion and chrysanthemum. The dermatitis improved on avoidance of handling plants. We have not documented any other cases of Compositae sensitivity in 187 other children, aged under 16 years, who have undergone patch testing with SL mix between 1992 and 1996 in our department. This case illustrates that Compositae sensitivity may present with a localized dermatitis and that, although uncommon, sensitization may occur in early childhood.

Reactive perforating collagenosis is an uncommon disorder and few accounts refer to ultrastructural features. This report includes a study by light and transmission electron microscopy of serially sectioned biopsies from early lesions in two patients. Immunohistological investigations utilizing antibodies to basement membrane, laminin, collagen and cytokeratin were also done. Collagen and elastin were demonstrated within the centre of the lesions and there was a defect in the basal lamina at the base of the lesion. The collagen, cytokeratin and the basal lamina in the lesions were antigenically similar to those in the surrounding normal skin. These results are compared with previous findings and discussed in the light of the current views on the pathogenesis of this disorder.

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