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 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.