present as crust on top of a primary lesion that has been partially scratched off. They are almost
exclusively confined to the eczematous diseases.
Lichenification: A typical skin thickening seen in chronic pruritus with recurrent scratching. Resembles
the callus formation of palms and soles after recurrent trauma. Lichenified skin is hardened, leather-like, with prominent markings and some scaling. Like excoriation, lichenification is typical of eczematous
diseases. In fact, it is considered pathognomonic of atopic dermatitis.
Scales: Raised lesions presenting as flaking of the upper skin surface. In fact, they represent thickening
of the stratum corneum, the uppermost layer of the epidermis. Scales may be white, gray, or tan. They
may also be small or rather large. They provide the squamous component to papulosquamous diseases.
They are extremely common in the scalp, where they suggest either banal processes (dandruff) or more
serious conditions (seborrheic dermatitis, psoriasis, and tinea capitis).
Crusts: Raised lesions produced by dried serum and blood cell remnants. Usually preceded by fluid-filled
primary lesions (i.e., vesicles, pustules, or bullae). The most familiar crust is the “scab” of impetigo.
Erosions: Depressed lesions produced whenever the epidermis is either removed or sloughed. They are
moist, usually red, and well circumscribed. Classic erosions are those of chickenpox following rupture of
Ulcers: Depressed lesions produced whenever not only the epidermis but also part (or all) of the dermis
is gone. Ulcers are concave, often moist, and at times inflamed or even hemorrhagic. They heal with
scarring. A classic ulcer is that of the syphilitic chancre.
Fissures: Depressed lesions presenting as narrow, linear, and vertical cracks that penetrate through the
epidermis, reaching at least part of the dermis. Classic fissures are those of the athlete’s foot.
Atrophy: Usually the nonspecific end-product of various skin disorders. It is characterized by a pale
and shiny area, with loss of cutaneous markings and full skin thickness.
Sinuses: Connective channels between the surface of the skin and deeper components.