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...