Warts are viral skin squatters with a way of overstaying their welcome. They can appear anywhere; on the soles of your feet, around your nails, or in places you’d rather not mention, and though not dangerous, these seemingly minor skin bumps are contagious and often maddeningly persistent.

Understanding what kind of wart you’re dealing with and why it’s so stubborn is the first step toward finding the proper treatment and keeping it from coming back.

What Are Warts, Exactly?

Warts are benign skin growths caused by a localized HPV infection in the top layers of the skin. Unlike viruses that travel through the bloodstream, HPV stays local, burrowing into a specific site after entering through a tiny cut, scrape, or compromised barrier.

Once inside, the virus triggers excess skin cell growth, resulting in a raised, often rough-surfaced bump that can vary in shape, size, and location. 

Why Are They So Persistent?

Part of what makes warts so frustrating is their ability to evade your immune system. Unlike systemic viruses that circulate through the bloodstream, HPV lives in the outermost layers of the skin, where immune surveillance is limited, so your body may not recognize the virus as something to fight off.

Even when your immune system does respond, it may not be enough to clear the virus entirely. In the meantime, warts can spread through self-inoculation, like shaving over a wart or picking at it, and pop up in new locations. Add in other factors like friction, moisture, and compromised skin barriers in the form of cracked heels or dry hands, and you have the perfect conditions for recurrence.

Types of Warts

While all warts stem from HPV, they don’t present the same way or respond equally to treatment. With over 150 types of HPV, identifying the type of wart can help determine both its cause and the most effective way to keep it from coming back. The different types of HPV are identified by numbers and are grouped based on whether they infect cutaneous (skin) cells or mucosal (genital) cells.

Cutaneous warts cause warts on top of the skin on areas like the hands, feet, face, legs and arms, while mucosal warts appear in areas such as the

  • Vagina, anus, cervix, and vulva (area around the outside of the vagina)
  • Inner foreskin and urethra of the penis
  • Inner nose, mouth, and throat
  • Trachea (windpipe) and bronchi (smaller breathing tubes branching off the trachea)
  • Inner eyelids

Cutaneous (skin) HPV types

Many HPVs are cutaneous types, meaning they enter and live in cells on the skin. Cutaneous HPVs can cause warts on top of the skin in areas such as hands, feet, face, arms, and legs. These are common warts that are only on the skin. They are not the same as genital warts.

Common Warts (Verruca vulgaris)

If you had warts as a kid, there’s a good chance it was the common wart: small, rough bumps that tend to cluster around your fingers, knuckles, or knees. These are caused by HPV types 2 and 4 (most common), followed by types 1, 3, 27, 29, and 57.

Kids are particularly prone to common warts, which spread easily through casual contact. Couple that with a still-developing immune system and the way they interact with the world; digging in dirt, sharing toys with half the playground, putting fingers in their mouths creating constant opportunities for the virus to enter through tiny cuts or scrapes.

In adults, these warts often appear in people who work with their hands, especially if frequent washing or glove use compromises the skin barrier.

Look for:

  • Raised, rough-surfaced bump
  • Skin-colored or grayish with a thickened texture
  • Often dotted with small black points (clotted capillaries)

Plantar Warts (Verruca plantaris)

Plantar warts develop on the soles of the feet, usually in high-pressure areas like the heels or balls of the feet. They’re caused by HPV types 1, 2, 3, 4, 27 and 57, which thrive in warm, damp environments like locker rooms and pool decks.

Teens are especially prone to plantar warts because of a perfect storm of factors: They’re more likely to go barefoot in communal spaces, they often have increased foot sweat due to puberty, and many participate in sports that create constant friction and pressure. All of that moisture and microtrauma softens the skin and weakens the barrier, giving the virus an easy way in.

Unlike most warts, plantar warts grow inward due to walking pressure, which can make them harder to spot and more painful to live with.

Look for:

  • Flat or indented lesion surrounded by thickened skin
  • May cause tenderness with pressure or walking
  • Can disrupt normal skin lines
  • Often dotted with small black points (clotted capillaries)

Flat Warts (Verruca plana)

Flat warts, which are linked to HPV types 3, 10, 28 and 49 are more subtle than other types because of how they present: smooth to the touch, nearly flush with the skin, and often misidentified as minor texture changes or breakouts, especially in younger patients.

You’ll usually find them on the face, neck, or backs of the hands areas where the skin experiences repeated friction or minor trauma from shaving, scratching, or even drying off with a towel. When that happens, it can spread the virus across the surface of your skin, causing new warts to form in a straight line in a response known as a Koebner phenomenon.

Look for:

  • Small, smooth, flat-topped bumps
  • Flesh-toned, pink, or light brown
  • Often appear in clusters or lines
  • Common on the face, forehead, arms, and hand

Filiform Warts (Verruca filiformis)

HPV types 1, 2, 4, 27, and 29 can lead to filiform warts, which grow vertically, forming long, narrow projections that rise above the skin. They tend to form on the eyelids, lips, or nose, where the skin is thinner and more mobile, and can develop very quickly. Though filiform warts are not typically painful, shaving or facial movement can irritate them further and they may be cosmetically distressing, making them feel more intrusive despite their small size.

Look for:

  • Long, thread-like projection above the skin
  • Flesh-colored or slightly darker
  • Most common around the mouth, eyes, nose, and chin
  • Can become irritated by shaving or facial movement.

Periungual Warts (Verruca periungualis)

Periungual warts, associated with HPV types 1, 2, 4, 5, 7, 27 and 57, begin as small, gritty patches that develop along the edges of fingernails or toenails.

Treatment can be especially frustrating because your hands rarely get a break, whether you’re washing dishes, typing, or working in construction. It’s much more difficult for the skin to heal fully, which allows the virus to continue to spread until the warts grow large enough to interfere with nail growth and grooming.

Department of Dermatology and Allergology, Friedrich Schiller University Hospital, Jena, Germany

Look for:

  • Rough, thickened skin around the nail edges
  • May lift or push against the nail plate
  • Can interfere with normal nail growth
  • Often slow to respond to treatment

Mucosal (genital) HPV types

Mucosal or genital HPV types are categorized into low-risk and high-risk types, depending on their ability to cause cancer.

Low-risk mucosal types

HPV 6 and HPV 11 are low-risk HPV types. They tend to cause genital warts and rarely cause cancer, although some of these types may have proteins in them, such as E6 and E7 that might add to their ability to cause cancer. Having a low-risk genital HPV infection can cause cauliflower-shaped warts on or around the genitals or anus. Warts may appear in areas that aren’t always noticed, such as the cervix and vagina.

High-risk mucosal types

HPV 16, HPV 18, HPV 31, HPV 33, and HPV 42 are examples of high-risk HPV types that can cause cancer. These HPV types can sometimes avoid the body’s immune system, so the body can’t get rid of the HPV. The infection causes damage to normal cells that can turn them into abnormal cells, which might later become cancer. High-risk HPV types are known to cause 6 different types of cancer; cervical, vulvar, vaginal, penile, anal and mouth and throat.

If there’s one takeaway, it’s that no two warts behave the same, so it’s easy to second-guess when and how to treat it.  When you’re dealing with wart worries or you’ve already tried to treat it without results, let Dr. Elizabeth Briden take a look. She can help you find the best treatment plan for you, which we hope you’ll come back next week to learn about!

Until then, reach out to schedule an appointment and get the personalized care you need to conquer even the most stubborn spots once and for all.