Skin Diseases

The skin is subject to many disorders. They occur through the direct action of external agents or as symptoms of disease in other parts of the body. Susceptibility to skin disorders is modified and sometimes determinate by generic factors.

Lesions
The appearance of abnormal changes, or lesions, in the skin is an important element in diagnosis and treatment. Various lesions can occur, not all of them diseases related. A flat lesion of a color differing from surrounding skin is called a Freckle. A papule is a solid, elevated by superficial mass, such as a raised Mole or a Wart. A wheal is a transitory lesion resulting from an allergic response, such as to an insect bite. A nodule is a solid mass that extends deeper, such as in certain tumors and cysts. A vesicle is a tiny blister filled with clear fluid, such as in early chicken pox. A bulla is a large blister, most often seen as the result of a coloration caused by deposits of blood or blood pigments within the skin.
The appearance of such lesions may be modified by secondary changes. These include scales or flakes of dead skin, as seen in Psoriasis and Dandruff; crusts, typically dried masses of material that have oozed out as in impetigo; fissures, or sharp breaks, as seen in athlete's foot; Ulcers, or destruction of one or more skin layers, exposing underlying tissue replacing lost tissue; and lichenification, a thickened scaly area in which normal skin creases and lines are exaggerated. Lesions may be seen in several different lesions.

Malignant Tumors
Any metastasizing tumor from else where in the body may appear in the skin. Many malignant tumors also originate in the skin. Four should be mentioned. Basal cell carcinoma may originate from basal cells of the epidermis. It almost never metastasizes, and it is easily cured. Squamous cell carcinoma does metastasize. Both tumors are common, especially in the elderly and in those overexposed to the Sun. Malignant melanoma derives from the same embryonic nervous tissue that produces moles. Finally, the once rare tumor called Kaposi's sarcoma has become more frequent because of AIDS.