What Are Plantar Warts?

Plantar warts (known scientifically as verruca plantaris) are small growths that appear on your feet. The warts are caused by certain strains of human papillomavirus (HPV) that enter your body through a break in the skin. It's believed that about 1% of the U.S. population has plantar warts, with most of these cases being in children.

These skin growths aren't typically serious, but for some people they can be embarrassing or painful enough to change the way they walk. Most plantar warts resolve on their own, but it can take weeks, months, or even years for this to happen. Fortunately, there are several options for removal.

Types of Plantar Warts

Plantar warts are generally categorized by how many there are and what their pattern is. Using this method, there are two ways to describe plantar warts: solitary and mosaic.

Solitary warts start as a single wart that may grow over time and multiply. The newer warts may form in a circle around the original wart, but there will be space between each one.

Mosaic warts refers to several plantar warts that grow close together in a cluster. They often feel rough and look like patches of thickened skin. Mosaic warts are generally harder to treat than solitary ones.

Symptoms

If you have a plantar wart, you'll most likely notice that a small patch of skin on your foot has changed. Although warts can form anywhere on the foot, they most often develop on the parts that have the most contact with the floor: the heel and base of the toes.

A plantar wart that forms on the sole of your foot tends to grow inward due to pressure. These warts are like icebergs in structure—with only a small portion of the wart visible on the outside. Thick tissue then often grows on top of the warts. That's why it's easy to confuse a plantar wart with a callus. If thick skin hasn't covered a wart that has grown inward, the wart may be harder to notice.

Other distinctive plantar wart features include:

• Appearing yellowish or grayish on lighter skin and lighter on darker skin
• Tiny black dots on the surface that form from broken capillaries
• Skin that doesn't contain the lines and ridges that cover the rest of the foot
• A gradual increase in size over time (some can grow bigger than an inch)
• Multiple warts in the same area

Some people with plantar warts feel pain or the sensation that there’s a pebble inside their foot when they move around. When squeezed, the wart may feel tender.

What Causes Plantar Warts?

A plantar wart develops when the immune system can’t fully fight off HPV. There are about 150 types of HPV. However, only about a dozen of them can cause plantar warts—and of those, only four strains are responsible for the vast majority of plantar warts. 

You can pick up the virus from direct contact with a plantar wart or from touching an infected surface. The virus enters the body through breaks in the skin, such as scrapes or spots that have been weakened by water. 

Not everyone infected with HPV will develop a wart. A plantar wart will develop if your immune system can't fight off the virus or doesn’t detect the virus because it's confined to the outer layer of skin. The lingering virus triggers an excess production of the hard protein keratin, which results in a wart.

Risk Factors

You’re more likely to come in contact with the types of HPV that cause plantar warts if you spend a lot of time with someone who has a plantar wart or walk barefoot in communal places such as such locker rooms, showers, and pool decks.

Plantar warts most often affect children between the ages of 5 and 16, possibly because they spend more time in common areas without shoes.

People who are immunocompromised are more susceptible to developing plantar warts because it's more difficult for them to fight off HPV.

If you've already had a plantar wart, you might be more susceptible to developing one again.

How Are Plantar Warts Diagnosed?

A healthcare provider will examine the soles of the feet and look for classic plantar wart features, such as small black dots. Sometimes they'll use a microscope to better examine the growth.

A close inspection should be able to rule out skin conditions that look similar, such as corns or calluses. However, in rare cases, a healthcare provider may want the skin biopsied for a more definitive diagnosis. This entails scraping off a portion of the wart and sending it to a lab for testing.

Treatment

The goal of treatment is to fully remove the plantar wart. If a wart isn't painful, a healthcare provider may recommend waiting to see if it resolves on its own. Otherwise, there are two common treatments.

Salicylic acid is often the initial go-to treatment. This is an over-the-counter or prescription beta hydroxy acid that’s also used to treat other skin conditions, such as acne and psoriasis. If effective, it will loosen layers of the wart until the entire wart disappears, usually after weeks or a couple months.

You might also undergo cryotherapy with liquid nitrogen. For this in-office procedure, a healthcare provider attempts to freeze the wart by applying liquid nitrogen with a cotton ball or spray. This forms a blister around the wart, and the dead tissue eventually falls off. The procedure can be painful and may cause permanent loss of skin color around the treated area. 

If these two treatments don't work or the wart has been there for more than six months, your healthcare provider may recommend alternative treatment. These treatments include:

• Cantharidin, a liquid that causes a blister to form under the wart
• Electrosurgery and curettage, which involves burning the wart before or after scraping it off 
• Laser treatment, in which a pulsed dye laser burns the wart and kills skin tissue 
• Chemical peels, which are prescribed topical medications that include high-strength salicylic acid, tretinoin, and glycolic acid 
• Bleomycin, which is an anti-cancer medicine that may be injected into the wart
• Shave excision, or numbing the skin and using a blade to remove the wart
• Immunotherapy, a last-resort strategy that involves topical treatment (usually diphencyprone) or shots (interferon) that boost your body's ability to fight off the HPV

How To Prevent Plantar Warts

You can help ward off plantar warts by taking measures to limit exposure to the HPV strains that cause them. Strategies to avoid HPV include:

• Not touching someone else’s wart
• Wearing shoes in communal areas, such as locker rooms, pool decks, and public showers
• Not sharing towels, shoes, socks, nail clippers, and other personal items with other people
• Covering cuts on your feet and moisturizing your feet to make it harder for HPV to enter your body
• Washing your hands often

You'll also want to prevent a pre-existing plantar wart from spreading. You can do this by:

• Touching your wart as little as possible
• Washing your hands after touching your wart
• Avoiding using items that have touched your wart, such as a washcloth, on other parts of the body
• Keeping your wart covered with something like a Band Aid or duct tape

No reliable evidence shows that the HPV vaccine can protect against plantar warts. The vaccine has been proven to prevent you from contracting the type of HPV that can lead to cervical cancer or genital warts.

Comorbid Conditions

If you have a plantar wart, there's a chance that it can lead to other health issues. One is additional plantar warts. This most often happens when the skin of an existing plantar wart sheds, as all skin does, and the virus breaks through nearby skin.

Some people may begin to change their walk to alleviate pain from putting pressure on their wart. Over time, this can cause new aches and pains.

In very rare instances, a plantar wart may turn into verrucous carcinoma, a type of highly treatable cancer that can also occur in the mouth and genitals. While it's unlikely to have a plantar wart that turns cancerous, it's more likely to happen to people who are immunocompromised. Cancerous lesions on the foot may be:

• Reddish in color
• More painful than plantar warts
• More crumbly than plantar warts

Living With Plantar Warts

Most people won't be seriously harmed by their plantar wart, but these little foot bumps may be embarrassing, painful, and frustrating. Although an estimated 70% of plantar warts resolve on their own, treatment can help the wart heal faster. Plantar warts that remain for more than six months tend to be more resistant to treatment. However, even the most stubborn warts have a chance of being cured through methods such as laser treatment or immunotherapy. 

As your wart heals, talk to a healthcare provider in the meantime about how you can alleviate wart-related pain. There are a number of strategies, including wearing shoes that put less pressure on your feet and cushioning the wart with patches or pads.