Warts are common skin growths often mistaken for fungal infections. They are benign proliferations of the skin that appear when surface cells grow at an accelerated rate. This growth is not caused by fungus, mold, or bacteria, but is instead entirely triggered by a viral infection. The appearance of a wart is the visible outcome of a highly specific biological process occurring within the skin layers.
The Definitive Cause: Human Papillomavirus (HPV)
The sole cause of warts is infection by the Human Papillomavirus (HPV). This DNA virus is highly prevalent, with over 200 types identified, though only a fraction cause the common skin warts that appear on the hands and feet. The virus gains entry into the body through tiny breaks, cuts, or abrasions in the skin’s outermost layer, the epidermis.
Once inside, the HPV targets the basal layer of the skin, where it infects the keratinocytes, which are the main cells that make up the epidermis. The viral DNA then instructs these cells to multiply more quickly and abnormally than normal skin cells. This rapid, uncontrolled growth of keratinocytes is what produces the characteristic raised, rough texture of the wart, a process known as epidermal hyperplasia.
Different types of HPV are responsible for specific wart appearances and locations. For instance, HPV types 2 and 4 are frequently associated with common warts, while HPV type 1 is a common cause of deep plantar warts on the feet. The resulting wart is essentially a mass of infected cells that continuously produce new viral particles, which can then be shed into the environment or spread to other parts of the body. The virus remains localized to the skin’s outer layers and does not spread systemically.
Understanding Transmission and Contagion
Warts are highly contagious because the HPV that causes them is easily transmitted through both direct and indirect contact. Direct transmission occurs through skin-to-skin contact with an existing wart on another person. The virus can also spread from an infected person to a surface, where it can remain viable for a period of time.
Indirect transmission happens when a person touches an object or surface contaminated with the virus, such as shared towels, razors, or certain public areas. Common environments for indirect spread include communal showers, locker room floors, and swimming pool decks, especially where people walk barefoot. The HPV is more likely to enter the skin if the surface is moist or if the skin has small breaks.
Not everyone who is exposed to the virus will develop a wart, as the immune system plays a determining role in whether the infection takes hold. The time between exposure to the virus and the appearance of a visible wart, known as the incubation period, can vary significantly, often taking several months. This latency period explains why it can be difficult to pinpoint the exact moment or source of the initial infection.
Variations in Wart Appearance and Location
Warts are classified based on their physical appearance and the location on the body where they develop, which often correlates with the specific HPV strain involved.
Common Warts
Common warts (verruca vulgaris) typically appear on the hands, fingers, and knees. They present as rough, dome-shaped growths with a grainy surface and often feature small black dots, which are the tips of clotted blood vessels.
Plantar Warts
Plantar warts develop on the soles of the feet. The pressure of walking causes them to grow inward rather than outward, often making them flat and surrounded by thickened, calloused skin. These can be painful, creating the sensation of stepping on a pebble.
Flat Warts
Flat warts (verruca plana) are distinct in that they are small, smooth, and only slightly raised above the skin surface, appearing flesh-colored, pink, or light brown. They frequently occur in large clusters on the face, arms, or legs. They are commonly spread in areas that are shaved, as the razor can move the virus across the skin.
Common Approaches to Wart Removal
Treatment for warts primarily focuses on destroying the infected skin tissue to eliminate the viral particles and stimulate an immune response against the HPV.
Over-the-Counter Treatments
Over-the-counter (OTC) options rely heavily on topical preparations containing salicylic acid, a keratolytic agent. This acid works by slowly dissolving the protein structure of the wart and peeling away the infected skin layers over a period of weeks or months.
Clinical Procedures
For more stubborn warts, clinical procedures are often necessary and are performed by a healthcare professional. Cryotherapy, which involves applying liquid nitrogen to the wart, is a common technique that rapidly freezes and destroys the tissue. The freezing causes blistering beneath the wart, leading to the eventual sloughing off of the dead tissue.
Other in-office treatments include electrocautery, which uses an electrical current to burn the wart away, and various forms of laser therapy that target the blood vessels supplying the wart. A physician may also recommend combining methods, such as using salicylic acid daily in conjunction with periodic cryotherapy treatments, which can increase the overall success rate.