Psoriasis. Light micrograph of a section through skin affected by psoriasis, a chronic skin disease causing inflammation and scaly lesions. The surface of the skin (stratum corneum) is at top. There is a parakeratotic layer (top) showing abnormal keratinisation and microabcesses (upper centre) immediately below the cornified layer. Beneath this, the stratum spinosum layer of the epidermis is greatly thickened (acanthosis). This is a major feature of psoriasis. The rete pegs (sections of epidermis, dark pink, that protrude into the dermis, light pink) and dermal papillae (sections of dermis that protrude into the epidermis) are elongated and pronounced.