Warts are caused by the human papillomavirus (HPV), of which there are more than 100 types. HPV probably infects the skin via areas of minimal trauma.

• Risk factors include use of communal showers, occupational handling of meat, and immunosuppression.

• In immunocompetent persons, warts are harmless and resolve as a result of natural immunity within months or years.

• For what is such a common condition, there are few large, high-quality randomized controlled trials (RCTs) available to inform clinical practice.

Topical salicylic acid increases complete wart clearance compared with placebo.

Cryotherapy may be as effective at increasing wart clearance as topical salicylic acid, but studies have been small and have had inconclusive results. We found insufficient evidence on the effects of cryotherapy versus placebo.

Photodynamic treatment may increase the proportion of warts cured versus placebo, although RCTs were small. It may increase pain or discomfort compared with placebo.

Contact immunotherapy with dinitrochlorobenzene may increase wart clearance compared with placebo, but it can cause inflammation.

We do not know whether intralesional bleomycin speeds up clearance of warts compared with placebo, because studies have had conflicting results.

We do not know whether cimetidine, formaldehyde, glutaraldehyde, homeopathy, duct tape occlusion, pulsed dye laser, surgery, or oral zinc sulfate increase cure rates compared with placebo, because we found few high-quality studies.

Definition

Nongenital warts (verrucae) are a common, benign, and usually self-limited skin disease. Infection of epidermal cells with HPV results in cell proliferation and a thickened, warty papule on the skin. There are more than 100 different types of HPV. The appearance of warts is determined by the type of virus and the location of the infection.

Any area of skin can be infected, but the most common sites are the hands and feet. Genital warts are not covered in this review. Common warts are most often seen on the hands and present as skin-colored papules with a rough verrucose surface. Flat warts most often occur on the backs of the hands and on the legs. They appear as slightly elevated, small plaques that are skin colored or light brown. Plantar warts occur on the soles of the feet and look like very thick callouses.

Incidence and Prevalence

There are few reliable, population-based data on the incidence and prevalence of nongenital warts. Prevalence probably varies widely with different age groups, populations, and periods of time. Two large population-based studies found prevalence rates of 0.84 percent in the United States and 12.9 percent in Russia. Prevalence is highest in children and young adults, and two studies in school populations have shown prevalence rates of 12 percent in four- to six-year-olds in the United Kingdom, and 24 percent in 16- to 18-year-olds in Australia.

Etiology and Risk Factors

Warts are most common at sites of trauma, such as the hands and feet, and probably result from inoculation of virus into minimally damaged areas of epithelium. Warts on the feet can be acquired from walking barefoot in areas where other persons have walked barefoot. One observational study (146 adolescents) found that the prevalence of warts on the feet was 27 percent in those who used a communal shower room and 1.3 percent in those who used a locker (changing) room.

Warts on the hand are an occupational risk for butchers and meat handlers. One cross-sectional survey (1,086 persons) found that the prevalence of warts on the hand was 33 percent in slaughterhouse workers, 34 percent in retail butchers, 20 percent in engineering fitters, and 15 percent in office workers. Immunosuppression is another important risk factor. One observational study in immunosuppressed renal transplant recipients found that 90 percent had warts five years or later after transplantation.

Prognosis

Nongenital warts in immunocompetent persons are harmless and usually resolve spontaneously as a result of natural immunity within months or years. The rate of resolution is highly variable and probably depends on several factors, including host immunity, age, HPV type, and site of infection. One cohort study (1,000 children in long-stay accommodation) found that two thirds of warts resolved without treatment within a two-year period. One systematic review (search date: 2005; 60 RCTs) comparing local treatments with placebo found that 48 percent of persons using placebo (range of 10 to 54 percent) had no warts by six weeks to 18 months after initiation of therapy.