The Langerhans cell: the master key to contact dermatitis: a hypothesis.

A tentative model is presented which is based on existing published data. The model suggests that the epidermal Langerhans cell plays a central role in contact dermatitis by proliferation control of keratinocytes and as the most peripheral outpost of the immune system. Contact dermatitis to chemicals is the injurious expression of a defense mechanism designed phylogenetically against arthropods and insects.