Because the skin is in contact with the environment, it is especially susceptible to injuries, such as abrasions (scraping), contusions (bruises), and cuts. Other common disorders of the skin may be subdivided into infectious and noninfectious disorders. Some inflammatory disorders may fall into either group, depending on the specific cause of the disorder. Common childhood diseases, such as chicken pox and measles, are not listed here but produce skin lesions that characterise the particular disease.

Infectious Disorders

Acne (ak’-ne) is a chronic skin disorder characterised by plugged hair follicles that often form pimples (pustules) due to infection by certain bacteria. It often appears at puberty, when sex hormones stimulate increased sebum secretion.

Athlete’s foot (tinea pedis) is a slightly contagious infection that is caused by a fungus growing on the skin. It produces reddish, flaky, and itchy patches of skin, especially between and under the toes, where moisture persists.

Boils are acute, painful Staphylococcus infections of hair follicles and their sebaceous glands as well as the surrounding dermis and subcutaneous tissue. The union of several boils forms a carbuncle.

Fever blisters, or cold sores, are clusters of fluid- filled vesicles that occur on the lips or oral membranes. They are caused by a Herpes simplex virus (type 1) and are transmitted by oral or respiratory exposure. Genital herpes, which is caused by either Herpes simplex virus type 1 or Herpes simplex virus type 2, results in the formation of painful blisters on the genitals as a result of infection transmitted by sexual activity.

Impetigo (im-pe-ti’-go) is a highly contagious skin infection caused by bacteria. It typically occurs in children and is characterised by fluid-filled pustules that rupture, forming a yellow crust over the infected area.

Non-infectious Disorders

Alopecia (al-o-pay’-she -ah) is the loss of hair. It is most common in males who have inherited male pattern baldness, but it may result from noninherited causes, such as poor nutrition, sensitivity to drugs, and eczema.

Bed bugs (Cimex lectulariur) are microscopic parasitic insects that feed almost exclusively off human blood. Their preferred habitats are sleeping areas in hotels and homes, but they can also be found in office buildings, movie theatres, and public transportation vehicles. Bed bugs exhibit peak feeding activity at night, with a preference for exposed areas of skin, and leave behind itchy welts. Washing infested clothes and bedding at 115° F (46°C) will kill bed bugs. Insecticides, deep cleaning of infested areas, and discarding mattresses are recommended for living areas and other contaminated areas.

Bedsores (decubitus ulcers) result from a chronic deficiency of blood circulation in the dermis and subcutaneous tissue. Bedsores form over bones that are subjected to prolonged pressure against a bed or cast. They are most common in bedridden patients. Frequent turning of bedridden patients helps to prevent bedsores.

Blisters, fluid-filled pockets, form when an abrasion, burn or injury causes the epidermis to separate from the dermis.

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