Skin infections
The skin is the largest organ in the human body. It is the front line of defense against many types of pathogens, and remains disease-free over most of its area most of the time. However, breaks in the skin are particularly prone to invasion by microorganisms, and skin infections are a relatively common complaint. Skin infections may be bacterial, viral or fungal in nature.
Among the more common bacterial skin infections is impetigo, a usually mild condition caused by staphylococcal or streptococcal bacteria. It causes small skin lesions and typically spreads among schoolchildren. Folliculitis results in pustules at the base of hairs or, in more serious cases, in painful boils. Often it is caused by Staphylococcus species. A relatively recent manifestation called "hot tub folliculitis" results from Pseudomonas bacteria in poorly maintained hot tubs. Those bacterial skin infections that do not resolve spontaneously are treated with topical or oral antibiotics.
Among the more serious bacterial infections of the skin is cellulitis, a deep infection involving subcutaneous areas and the lymphatic circulation in the region as well as the skin itself. The affected area is painful, red, and warm to the touch, and the patient may be feverish. Cellulitis is usually caused by bacterial invasion of an injury to the skin. Treatment includes oral and/or intravenous antibiotics, and immobilization and elevation of the affected area.
Viral skin infections typically show up as warts caused by the Human Papillomavirus (HPV). Common warts usually appear on the extremities, especially in children and adolescents. Plantar warts often grow on the heel or sole of the foot, surrounded by overgrown, calloused skin. When they develop on weight-bearing surfaces such as the heel, plantar warts may become painful. HPV also causes genital warts, or condylomata, which may increase the risk for cervical or penile cancer. Many methods are used in attempts to remove warts, with varying degrees of success. These include cryotherapy, antiviral agents, application of salicylic acid, surgical removal, and laser treatment.
Skin infections caused by fungi, including yeast, are called dermatomycoses. A common subcategory consists of the dermatophytoses, caused by Trichophyton species. These infections include tinea capitis ("cradle cap"), tinea corporis ("ringworm"), tinea cruris ("jock itch"), and tinea pedis ("athlete's foot"). Candida, which often affects the mucous membranes, may also be responsible for skin infections. Obese patients are prone to fungal infections in skin folds, as are uncircumcised men. Candida is also involved in some cases of diaper rash. Fungal infections are typically treated with topical imidazole creams or sprays.