It is generally thought that about 50 percent of all warts will spontaneously resolve within six months. However, some warts may remain at the same location with no apparent change for many years and others will continue to spread, expand or enlarge with time. Warts are generally self-limiting and very harmless but may cause symptoms due to the fact that they are unsightly, cause embarrassment, impede function, become irritated or cause pain. Verrucae are commonly termed warts. These are benign intraepidermal neoplasms caused by a variety of different viruses. Papillomaviruses belong to the family Papovaviridae and are species-specific, double-stranded DNA viruses. There are approximately 150 different human papillomaviruses (HPV) that have been implicated in the formation of human warts. The HPV types are listed numerically by their DNA composition for identification purposes. Individual variations in cell-mediated immunity may explain the differences in the size, severity, location and duration of warts. This may also explain why some warts respond readily to simple treatment while others appear to be extremely resistant to most forms of therapy. A Few Thoughts About Differential Diagnosis Clinically, warts obscure the normal visible skin lines and this usually helps to differentiate the wart from other lesions with a similar clinical appearance. Contrary to popular misconception, there are no “roots” penetrating into the dermis or subcutaneous layers. There is, in many cases, a single point in the wart tissue that is thicker or deeper than adjacent wart tissue. This may make the wart appear to be on a stalk or have a deep rooted base, which is probably the source of the mistaken belief in roots. Small thrombosed blood vessels may become entrapped in the cylindrical projections formed by the virus and are seen as small black dots on the surface of some warts. It is not always possible to identify a skin lesion as a wart simply based upon its appearance. The most common group of lesions in the differential diagnosis include: acquired digital fibrokeratoma, actinic keratosis, arsenical keratosis, cutaneous horns, lichen planus, molluscum contagiousum, prurigo nodularis, seborrheic keratosis and squamous cell carcinoma. Many of these lesions require a biopsy for positive identification. How To Differentiate Between Different Warts The most common lower extremity warts are common warts (verruca vulgaris), plane or flat warts (verruca plana), cylindrical (or digitate) warts, peri- and subungual warts, plantar warts and mosaic warts (see “A Review Of Common Lower Extremity Warts” below). Common warts. The common wart starts as a smooth, flesh-colored papule and eventually evolves into a dome-shaped, discolored, thickened growth with hemorrhagic or small thrombosed capillaries. Generally, these warts are few in number and are common on the non-weightbearing surface of the lower extremities. Common warts may range in color from light brown and slightly erythematous to darkly pigmented. They vary in size from 1 millimeter to well over 1 centimeter in diameter and may coalesce to produce larger lesions. Flat or plane warts. Flat or plane warts are also referred to as juvenile warts. They are very small lesions with a slightly raised, smooth, skin-colored or slightly pigmented, flat surface. These flat warts usually do not have the typical rough warty appearance or vascular display of other warts. They may occur along a pressure area or an area that has been scratched (Koebnerized), and are usually multiple and linear in arrangement. You’ll frequently see these warts on the lateral aspect of the foot or ankle. These flat warts are extremely likely to undergo spontaneous remission or involution but may be extremely persistent and unresponsive to therapy. Be aware that if you mistake these lesions for inflammatory conditions and treat them with topical corticosteroids, they will usually spread. Cylindrical warts. These warts, also known as digitate warts, are less common on the foot but you may see them on the toes. They are more frequently found on the face, neck or anogenital region. These growths consist of a few or multiple fingerlike projections that emanate from a single base. They may have visible capillaries within the cylinders that bleed easily with trauma or manual trimming. Periungual warts.