SKIN AND MUCOUS MEMBRANE INFECTIONS
Infection may primarily involve the skin and mucous membranes, or skin lesions may indicate infection elsewhere. The most common bacterial skin diseases include those caused by staphylococci, which tend to form boils (or pus-filled areas of inflammation), and streptococci, which result in a spreading area of skin inflammation. Measles, a systemic infection, is characterized by a generalized skin rash. Herpes simplex virus causes cold sores, and in impaired hosts, more widely spread lesions. Shingles, or herpes zoster, is an infection of the nerves supplying a specific area. The virus, identical to that which causes chicken pox, is thought to represent a reactivation of an old chicken pox infection. Diagnosis is usually easily made, because lesions characteristically cluster in a pattern representing the distribution of nerves on the surface of the skin. Parasites may invade the skin. For example, scabies is due to a small mite that burrows in the skin, causing intense itching and inflammation. The louse, which lays its eggs (nits) on hair, and ticks, which suck blood from the host, may transmit serious diseases. Fungal skin diseases, which are common and usually benign, include ringworm, athlete's foot, and thrush.