Fungal, Bacterial, and Viral Infections of the Skin

The skin can become infected by viruses, fungi, and bacteria, including some that ordinarily are harmless colonizing organisms. The most common fungal infections are caused by dermatophytes, which can involve the hair, nails, and skin. Potassium hydroxide (KOH) preparations of specimens from affected areas typically demonstrate hyphae, and either topical or systemic antifungal therapy usually cures or controls the process. The most common bacterial pathogens are Staphylococcus aureus and group A streptococci, which, alone or together, can cause a wide variety of disorders, including impetigo, ecthyma, and cellulitis. Topical antibiotics may suffice for impetigo, but ecthyma and cellulitis require systemic treatment. S. aureus, including methicillin-resistant strains, can also cause furuncles, carbuncles, and cutaneous abscesses. For these infections, incision and drainage without antibiotics are usually curative. Warts are the most common cutaneous viral infection, and eradication can be difficult, especially where the skin is thick, such as the palms and soles, or the patient is immunocompromised. Most therapies consist of trying to destroy the viruses by mechanical, chemical, or