Eczema is a heterogeneous disease and the pathophysiological mechanism should be clarified in each disease. Allergic contact dermatitis and atopic dermatitis are representative diseases showing eczematous reaction. A major player in both allergic contact dermatitis and atopic dermatitis is skin-specific T lymphocytes. The significance of these T lymphocytes, especially the expression of cutaneous lymphocyte-associated antigen on T helper cells types 1 and 2, and its counter-receptor on vascular endothelial cells needs further investigation. The evidence showing that infiltrating T cells participate in the formation of eczematous reaction through Fas-induced apoptosis is important in our understanding of eczematous reactions and also for treatment.