Disorders of the Skin
The skin is subject to many disorders, some of which are more annoying than they are life threatening. For example, athlete's foot is caused by a fungal infection that usually involves the skin of the toes and sales. Impetigo (im"peti'go) is a highly contagious disease occurring most often in young children. It is caused by a bacterial infection that results in pustules that crust over. Eczema (ek'ze-mah) and psoriasis (so-ri'ah-sis) are due not to an infection, but to overactive cell division, which results in areas of scaling and itching. Eczema is caused by sensitivity to various chemicals (soaps or detergents), to certain fabrics, or even to heat or dryness. Psoriasis is a chronic condition, possibly hereditary, in which the skin develops pink or reddish patches covered by silvery scales. Its cause is unknown, but outbreaks may be triggered by stress or infections. Dandruff is a skin disorder not caused by a dry scalp, as is commonly thought, but by an accelerated rate of keratinization in certain areas of the scalp, producing flaking and itching. Urticaria (ur"tI-ka'reah), or hives, is an allergic reaction characterized by the appearance of reddish, elevated patches and often by itching.
Skin Cancer
Skin cancer is categorized as either melanoma or nonmelanoma. Melanoma, the malignant type of skin cancer, starts in the melanocytes and has the appearance of an unusual mole. Unlike a normal mole, which is dark, circular, and confined, a melanoma mole looks like a spilled ink spot, and a single melanoma mole may display a variety of shades. A melanoma mole can also itch, hurt, or feel numb. The skin around the mole turns gray, white, or red. Melanoma is most common in fair-skinned persons, particularly if they have suffered occasional severe bums as children. Melanoma risk increases with the number of moles a person has. Most moles appear before the age of 14, and their appearance is linked to sun exposure. Melanoma rates have risen since the turn of the century, but the incidence has doubled in the last decade. Now, rediagnosed each year,
The most common type of skin cancer, begins when ultraviolet (UV) radiation causes epidermal basal cells to form a tumor, while at the same time suppressing the immune system's ability to detect the tumor. The signs of a tumor are varied. They include an open sore that will not heal; a recurring reddish patch; a smooth, circular growth with a raised edge; a shiny bump; or a pale mark. About 95% of patients are easily cured, but reoccurrence is common.
Squamous cell carcinoma begins in the epidermis proper. While five times less common than basal cell carcinoma, it is more likely to spread to nearby organs, and Raised growths on the skin, such as moles and warts, usually are not cancerous. Moles are due to an overgrowth of melanocytes, and warts are due to a viral infection.
Skin cancer is associated with ultraviolet radiation and occurs in three forms. Malignant melanoma is the most dangerous forrn of skin cancer. Squamous cell carcinoma and basal cell carcinoma are less severe forms and can usually be removed surgically.
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