Warts are infections of the epidermis with human papillomavirus (HPV). Warts that involve the periungual skin or subungual area are typically associated with HPV subtypes 1, 2, 4, 27, and 57. Butcher's warts may also affect the nail apparatus and are due to HPV 2 and 7. Warts are the most common nail tumor and affect fingernails more frequently than toenails. Warts are spread by human contact or indirectly via fomites on surfaces. Infection is more likely to occur when the skin is macerated or traumatized.

Warts involving the nails are fairly common in children. Warts of all kinds reach their peak prevalence in childhood and adolescence. Risk factors include atopic dermatitis, immunosuppression, nail biting, and nail picking.

In adults, warts are especially common among transplant patients and in individuals immunosuppressed due to human immunodeficiency virus infection (HIV), malignancy, or medications. They are also common in adults who do wet work, as well as in nail biters and nail pickers. There is a subset of ungual warts due to HPV 16 and 18 that are at higher risk of transforming into squamous cell carcinoma.