Plantar warts are growths on the soles of the feet caused by certain strains of the human papillomavirus (HPV). Their distinct appearance is shaped by their location on the plantar surface, where the constant pressure of walking and standing flattens the growth. This pressure forces the wart tissue inward, often making it feel like walking on a small stone. A plantar wart can become quite painful due to this inward growth and the resulting pressure on surrounding nerve endings.
Where Plantar Warts Form and Their Shape
Plantar warts commonly develop in weight-bearing areas of the foot, though they can appear anywhere on the sole. Because of the downward force, the wart does not project outward like warts on other parts of the body. Instead, it appears flat or slightly depressed into the skin, often covered by a layer of hard, thickened skin.
The wart is usually skin-colored, whitish, or yellowish-brown. It presents as a grainy or rough patch with a defined border, distinguishing it from the surrounding smooth skin. In some cases, a tight cluster of small warts forms a larger patch, known as a mosaic wart. When a thick callus forms over the core, the viral tissue may only be visible as a small, central “eye” surrounded by the hardened skin.
Key Visual Signifiers: Black Dots and Skin Lines
The primary visual marker for a plantar wart is the presence of tiny black dots. These specks are actually the ends of small blood vessels, called capillaries, that have clotted within the wart tissue (thrombosed). These capillaries grow into the wart to supply it with blood; the constant pressure on the foot causes them to rupture and clot, appearing as dark spots.
These black dots are often visible on the surface, but they become much clearer if the top layer of hard, callused skin is gently filed away. Once the protective callus is removed, the overall surface of the wart appears rough, granular, or bumpy. Another distinguishing feature relates to the normal skin lines, or dermatoglyphics, on the sole of the foot.
Healthy skin lines are parallel and will continue across the surface of a callus. In contrast, the abnormal growth of the plantar wart tissue disrupts this pattern. This disruption causes the normal skin lines to stop abruptly at the wart’s border and go around the lesion instead of through it.
Distinguishing Plantar Warts from Calluses
Plantar warts are frequently confused with calluses because both are areas of thickened skin found on the bottom of the foot. A callus is a defense mechanism where the body thickens the skin in response to repeated friction or pressure. Unlike warts, calluses are not caused by a viral infection and are not contagious.
The black dots, which are clotted blood vessels, are absent in a callus, which is composed only of dead skin cells. A difference in pain response provides another clue for identification. Calluses cause pain only when direct pressure is applied straight down onto the spot. A plantar wart is more painful when the lesion is squeezed from side-to-side, as this lateral compression pinches the inward-growing tissue against nerve endings.