Excessive thickening of stratum corneum with desquamation
Fine scales (pityriasiform) to coarse (psoriasis)
Color: white, gray, yellow
Size: mm to cm
Desquamation refers to diffuse shedding of scales. Special form: collerette with the scaling at the border of the lesion.
May appear anywhere on body surface: when localized often favours the palms and soles; may be generalized as in ichthyosis.
May develop erosions or crusts. Associated with papules, pustules and plaques.
Comment / Explanation
Localized keratosis with excessive scales such as cutaneous horn
Lichenification (thickened, scaly epidermis)
Inflammation: psoriasis, atopic dermatitis
Ichthyosis, xeroderma (dry skin), keratoderma
Excessive hyperproliferation of epidermal layers, loss of adhesion of keratinocytes.