April 16, 2007

Viral Skin Infections


Many viral infections—such as measles, chickenpox, and rubella—result in rashes, spots, or sores on the skin. Herpes viruses often produce rashes and sores. However, in two common infections, warts and molluscum contagiosum, the virus remains solely within the skin

Molluscum Contagiosum
Molluscum contagiosum is infection of the skin by a poxvirus that causes flesh-colored or white smooth, waxy bumps.

The bumps are usually less than ¼ inch in diameter and have a tiny dimple in the center. The virus that causes molluscum is contagious; it spreads by direct skin contact and is common in children (see Problems in Infants and Very Young Children: Rashes). Genital lesions are often transmitted sexually in adults.

Molluscum can infect any part of the skin. The bumps usually are not itchy or painful and may be discovered only coincidentally during a physical examination. However, the bumps can become very inflamed (resembling a boil) and itchy as the body fights off the virus. This inflammatory response may herald the disappearance of the lesions.

Most growths disappear spontaneously in 1 to 2 years; no treatment is needed unless they are disfiguring or otherwise bothersome. The growths can be treated by freezing or removing their core with a needle or sharp scraping instrument (curette). Sometimes doctors give high doses of cimetidine by mouth or apply trichloroacetic acid or cantharidin to molluscum. Others prescribe retinoic acid or imiquimod cream, which is applied for weeks or months.

Warts (verrucae) are small skin growths caused by any of 80 or more related human papillomaviruses.

Warts can develop at any age but are most common in children and least common in older people. People may have one or two warts or hundreds. Because prolonged or repeated contact is necessary for the virus to spread, warts are most often spread from one area of the body to another rather than from one person to another. Sexual contact, however, is often sufficient to spread genital warts (see Sexually Transmitted Diseases (STD): Genital Warts).

Most warts are harmless, although they may be quite bothersome. The exceptions are certain types of genital warts that sometimes cause cervical cancer in women.


Some warts grow in clusters (mosaic warts); others appear as isolated, single growths. Warts are classified by their location and shape.

Common warts (verrucae vulgaris), which almost everyone gets, are firm growths that usually have a rough surface. They are round or irregularly shaped; are gray, yellow, or brown; and are usually less than ½ inch across. Generally, they appear on areas that are frequently injured, such as the knees, face, fingers, and around the nails (periungual warts). Common warts may spread to surrounding skin.

Plantar warts develop on the sole of the foot, where they are usually flattened by the pressure of walking and are surrounded by thickened skin. They tend to be hard and flat, with a rough surface and well-defined boundaries. Warts may appear on the top of the foot or on the toes, where they are usually raised and fleshier. Warts are often gray or brown and have a small black center. Unlike corns and calluses, plantar warts tend to bleed from many tiny spots, like pinpoints, when a doctor shaves or cuts the surface away with a knife.

Filiform warts are long, narrow, small growths that usually appear on the eyelids, face, neck, or lips.

Flat warts, which are more common in children and young adults, usually appear in groups as smooth yellow-brown, pink, or flesh-colored spots, most frequently on the face and tops of the hands. The beard area in men and the legs in women are also common locations for flat warts, where they may be spread by shaving.

Genital warts (venereal warts, condylomata acuminata) occur on the penis, anus, vulva, vagina, and cervix. They are irregular, bumpy growths often with the texture of a small cauliflower

Symptoms and Diagnosis

Warts are painless, except for plantar warts. Plantar warts can be very painful when pressure is placed on them in the course of weight bearing.

Doctors recognize warts by their typical appearance. Growths on the skin that cannot be definitely identified may need to be removed for examination under a microscope (biopsy).


Many warts, particularly common warts, disappear on their own within a year or two. Because warts rarely leave a scar when they heal spontaneously, they do not need to be treated unless they cause pain or psychologic distress. Genital warts are more likely to persist and are more contagious, so doctors often remove them or treat them with drugs. All types of warts may recur after removal. Plantar warts are the most difficult to cure.

In general, warts can be removed with chemicals, cut off, frozen off, or burned off with a laser or electrical current.

Typical chemicals used for removal include salicylic acid, formaldehyde, glutaraldehyde, trichloroacetic acid, cantharidin, and podophyllin. Flat warts are often treated with peeling agents such as retinoic or salicylic acid. 5-Fluorouracil cream or solution may also be used. Some chemicals can be applied by the person, whereas others must be applied by a doctor. Most of these chemicals can burn normal skin, so when they are applied at home, it is essential to follow directions carefully. Chemicals usually require multiple applications over several weeks to months. The wart is scraped to remove dead tissue before each treatment.

Freezing (cryotherapy) is safe and does not usually require any numbing of the area but may be too painful for children to tolerate. Warts may be frozen with various commercial freezing probes or with liquid nitrogen sprayed on or applied with a cotton swab. Cryotherapy is often used for plantar warts and warts under the fingernails. Multiple treatments at monthly intervals are often required, especially for large warts.

Burning and cutting warts off is effective but is more painful and usually leaves a scar. A pulsed dye laser is also effective but, like freezing, usually requires multiple treatments.

Imiquimod is a new cream for the treatment of genital warts, which some doctors are using on other kinds of warts as well.

Adapted from: Merck & Co. Inc