The lesions are those of psoriasis, driven by T lymphocyte elaboration of cytokines driving cellular proliferation so that the normal sequence of keratinocyte maturation is disrupted. Acanthosis refers to epidermal hyperplasia, in which the thickness of the entire epidermis is increased. Dyskeratosis refers to premature keratinization below the stratum granulosum. Hyperkeratosis is an increased thickness of the stratum corneum with abnormal keratin; a callus would refer to thickened stratum corneum in response to mechanical forces, such as the hands of a carpenter working with tools, or the soles of the feet of a child going barefoot. Spongiosis is edema between the cells of the epidermis.