Lichen planus. Light micrograph of a section through skin affected by lichen planus, a clinically and histologically distinct form of dermatitis. The epidermis (upper layer) shows hyperkeratosis (flaky, red), above a thickening of the granular layer (dark pink). Below this there is acanthosis in the prickle cell layer (also dark pink). The basal layer shows characteristic hydropic degeneration, producing rete pegs (finger-like) and an irregular junction between the epidermis and the dermis (lower layer, light pink). The dermis shows a layer of dense chronic inflammatory cells.