The morphologic pattern is helpful in determining the offending agent.
Microvesicular dermatitis suggests allergic contact dermatitis, such as poison ivy dermatitis.
Photodistributed or streaky macular erythema suggests a phytophotodermatitis, such as lime, fig or meadow parsnip dermatitis. Agave dermatitis is seen among landscapers who come in contact with the juice from the leaves of the agave plant. Agave dermatitis is an irritant contact dermatitis, resulting in varying degrees of epithelial and vascular necrosis. The vascular necrosis results in purpura. Streaks of dermatitis suggest a point source of allergen.