Wart

Warts are non-cancerous growths that appear on the skin.

While they can look unusual, they are fundamentally different from cancerous tumors. Warts are caused by a viral infection rather than uncontrolled cell growth. Specifically, they are triggered by the human papillomavirus, or HPV. There are approximately 130 known types of HPV. Each type of the virus typically targets specific areas of the body. Most warts are benign, meaning they are not harmful to otherwise healthy people. However, they are incredibly common, affecting an estimated 1% to 13% of the general population.

The mechanism of a wart begins when the virus enters a host. This usually happens through a small wound or break in the skin. Once inside, the HPV infects the squamous epithelium. This is the layer of cells that makes up the skin and the genitals. The virus then causes the skin cells to grow in a specific way. Under a microscope, this looks like thickening of several skin layers. This includes the stratum corneum and the stratum spinosum. These layers are known as hyperkeratosis and acanthosis. The infection also causes the blood vessels at the junction of the skin layers to become large.

Warts are categorized into several distinct types based on their appearance and location. Common warts, or verruca vulgaris, are raised and have a rough surface. They are most frequently found on the hands. Flat warts, known as verruca plana, are small, smooth, and flesh-colored. They often appear in large numbers on the face, neck, or knees. Filiform warts look like thin threads or fingers and often grow near the eyelids or lips.

Plantar warts, or verruca plantaris, are hard lumps found on the soles of the feet. These often appear on pressure points and may contain small black specks. Other types include periungual warts, which grow around the nails, and mosaic warts, which are tight clusters of plantar-type warts.

Humans have recognized these growths for thousands of years. The Greek physician Hippocrates described warts as far back as 400 BC. Since then, medical understanding has shifted from simple observation to identifying the specific viral causes. We now know that different HPV types lead to different results. For example, HPV types 2 and 4 are common causes of standard warts. In contrast, "high-risk" HPV types, such as 16 and 18, are associated with serious conditions like cervical cancer. This distinction is vital for modern medicine and public health.

Prevention and treatment are major focuses of modern science. To prevent non-genital warts, people can wear shoes in public areas like locker rooms or showers. For genital warts, which are often sexually transmitted, barrier methods like condoms are used. Vaccines like Gardasil 9 provide significant protection. This vaccine targets several specific HPV types, including 6, 11, 16, 18, 31, 33, 45, 52, and 58. While these vaccines help prevent genital warts and certain cancers, they do not protect against the strains that cause plantar warts.

If warts do not resolve on their own, several medical treatments are available. Many warts disappear naturally within months or years. If treatment is needed, doctors might use cryotherapy. This process involves freezing the wart, often with liquid nitrogen.

Another option is applying salicylic acid directly to the skin. For more resistant cases, doctors may use lasers. A pulse dye laser works by absorbing the light into blood cells. A carbon dioxide (CO2) laser works by absorbing water molecules to vaporize the tissue.

Other advanced methods include using chemotherapy agents like fluorouracil or injecting drugs like bleomycin.

Understanding the biology of warts connects to the broader study of virology and immunology. The way the body reacts to HPV shows how our immune systems interact with pathogens. For instance, some treatments like imiquimod work by encouraging the body to produce interferon. Interferon is a protein that helps the immune system fight viruses. By studying these small growths, scientists gain a deeper understanding of how viruses manipulate human cells. This knowledge helps improve vaccines and treatments for many different types of infections worldwide.