Histologic aspects of patch test reactions in allergic contact dermatitis.

Twenty subjects with allergic contact dermatitis were patch tested with the responsible allergen applied to four fixed points on the back. Skin biopsies of the four sites were obtained after 6, 12, 24 and 48 hours, fixed in neutral formalin and stained with hematoxylin-eosin, Giemsa and toluidine blue. Sections were examined and lymphomonocytes, mast cells, eosinophils and basophils counted. In all cases the infiltrate consisted mainly of lymphomonocytes (80-82%); mast cells (5%) and basophils (0.2%) do not present clear variations within the given time. Eosinophils showed a definite numerical increase in six cases out of 20.