Warts are superficial viral infections of the skin and are very common in children. They are caused by infection with the human papillomavirus (HPV). Transmission of HPV is very easy owing to its survival on the skin, fomites, and surfaces, and it can be transmitted from person to person and from one area of the body to another on the same person. Approximately 30% of children develop warts, and they are more common in those with atopic dermatitis [7]. Treating palmoplantar and periungual warts can be challenging. For this reason, a variety of treatments are used, often in combination.

Therapies for pediatric warts are characterized according to six major categories: destructive (salicylic acid, cryotherapy, cantharidin, podophyllotoxin, topical retinoids); immune stimulating (imiquimod, orally administered cimetidine, squaric acid, diphencyprone, intralesionally administered candida antigen); immune modulating (zinc, plerixafor); vascular destructive (pulsed dye laser); irritant (duct tape); photodynamic therapy and nitric oxide releasing [7, 8]. Therapies for children must be safe and preferably painless; this is very important because two-thirds of warts will resolve without treatment within 2 years [1]. The much lower scores for pain and burning sensation that were reported with NZCS use in this study (mean pain score, 0.24; mean burning score, 2.49) than for previous treatments (mean pain score of 4 for cryotherapy; mean burning score of 6.50 for cryotherapy and for salicylic acid) indicate that this is a more comfortable approach for children.

Nitric–zinc complex solution is an aqueous solution, commercially available, containing organic acids (lactic, oxalic, and acetic acid at 8.6% each), small amounts of metallic ions (zinc and copper salts), and 65% nitric acid as the leading compound with a caustic effect that causes “mummification”, protein denaturation, and coagulation of the wart. NZCS has been useful in the treatment of palmoplantar and genital warts in adults, as reported in previous publications [5, 6, 9, 10]; we are now able to provide data on its use in a pediatric population. The strengths of the study are that it provides new data on this treatment in a pediatric population, in a prospective study design; limitations include the small sample size, single-center design, and absence of a control group, although some data were available on tolerability (pain/burning) in patients who had had different previous treatments.

In this study we demonstrate the efficacy and excellent tolerability of NZCS in pediatric patients with palmoplantar and periungual warts known as “difficult-to-treat” warts due to the location, with less pain and discomfort than previous treatments. According to our results, NZCS was useful in a pediatric population with viral warts including cases that had been resistant to previous treatment, from 4 years old. The painless nature of the technique, the simplicity of administration in the clinic, and the twice-monthly dosing regimen represent an advantage over other existing treatments. More studies are needed to evaluate the rates of recurrence of viral warts after treatment with NZCS in children and adolescents as in adults.