Doc, is this a planter's wart?

One of the most stubborn things on the feet to get rid of are plantar warts. "Why is it called that?" you may ask. That's because naming it requires a little bit of medical lingo. The surface of the bottom of the foot is called the plantar surface. Your body has lots of surfaces to name, including a long list that I typed out and after thinking better about throwing around a lot of technical jargon, I've erased. All the name of the surface indicates is which direction the surface faces in relation to the body, the hand, the foot, etc. So when you have a plantar wart, it has nothing to do with gardening--it merely states you have a wart on the underside of your foot.

What is a wart and why is it so stubborn?

A wart is simply a virus that grows on the skin. A plantar wart is particularly a virus that is located on the bottom of the foot. They are cousins to the strain of virus that causes genital warts and cervical cancer (don't worry, they can't spread from your foot to... other places). This is the Human Papilloma Virus. There are 17 strains known of HPV, but only a couple can cause plantar warts and none of those are the ones your OB/GYN worries about.

The reason these are so stubborn is because of the location they're found. Many of you have probably had a wart frozen off before. Usually this is on a hand or something. This works pretty well for warts that are anywhere but beneath the foot. That's because when the wart is commandeering your skin cells and growing, there's not usually pressure on the top of the wart, so it grows upward and outward, like a sapling growing into a treelike a little mound of tissue on your finger or elbow. When it grows on the underside of the foot--the plantar surface--there is pressure on the skin because unless you walk everywhere on your hands (or you crawl, or roll, or something like that), there is always something pressing on it, so it expands deeper into the skin.

Because of all of the compression that happens, the wart gets deeper in the skin and a tough callus forms on top of it. It gets flatter and wider, while losing the cylinder shape of other warts. The little black dots on the top that are often called the "seeds" of the wart by people are actually the tops of little capillary loops that have grown up into the wart because of the wart's effect on the local tissue. I like to envision it as an invading army attempting to set up shop behind enemy lines by building a weapon factory along a river where they can use the local shipping channels to easily get supplies needed to continue building.

When it is embedded in the skin like that, the wart becomes insulated from temperature, so "freezing" the wart is less effective. Only the very tip-top of the wart gets cold, nowhere near where the deepest infected cells are, so it never really dies out completely. Because of this, other treatments need to be considered.

Effective Treatments

Treating a plantar wart requires one of two main treatment types either removing the whole infected area at once (freezing is this option for other wart locations) or speeding up the growth of the skin cells so they are shed by the body before they can infect the cells beneath them. This is usually done using salicylic acid (SA). Many SA formulations are over the counter but come in weaker concentrations than most prescriptions. These are often less painful options (I usually use a route like this on kids) but they work much slower.

The Goal with Salicylic Acid treatment is to speed up the "Conveyor Belt"

The more aggressive treatment option is to figuratively "drop a bomb" on the wart (sorry, another military metaphor), cratering out the whole area where infection is found. The options for this are varied but effective. Commonly you will find a medication called bleomycin that is often used to treat skin cancers. This is injected into the skin and kills all the cells in the skin in that area. Another option is called cantharidin. This is a personal favorite--because I'm a nerd--and it is a compound isolated from a variety of beetles (somewhere back in history people noticed that if you touched a certain beetle with your skin, a large blister would form there). This gets placed on the wart and the blister kills all the cells in a certain area, taking with it the infected ones. For more information, you can Google it, or click here for a riveting read by the University of Florida

The goal of this treatment is to get rid of the area where the
infected cells live and then allow the skin to heal back

Another medication exists that gets injected into the cells that is commonly used, but causes an immune response in the area, rather than killing everything indiscriminately. This is candida antigen. Basically, warts aren't recognized by the immune system because it lives in the skin, where most of the time it is invisible to the cells that recognize infection. You inject a protein from a yeast (no, you won't get a yeast infection from this injection) into the area and your body quickly realizes something is wrong and attacks the protein, taking with it the cells in the area.

The last way to crater out the zone of infection is to physically cut it out. This is not my preferred option because the recovery is pretty painful, but I will do this on occasion for very stubborn warts. The principle remains the same: remove the infected cells, there's no more infection. Most people would prefer one of the other options because often the idea of surgery is terrifying.

One more procedure exists in which you cut out a wart, turn it upside down, and sew it underneath the skin, exposing your body's immune system to it and causing a targeted attack of the virus. I have a number of doctors I've trained under who love the procedure for especially stubborn warts, but it's a bit overkill for most warts.

There are some conditions that mimic warts, and not all of them are easy fixes, so I recommend getting looked at by a specialist. This is especially true if you've tried treatments yourself and failed, or if the spot on your skin has any type of pigment to it. Skin cancers to the untrained eye can look like warts, or calluses, or any number of benign thing, so don't be afraid to ask for help--that's what we do best!

Again, the rudimentary diagrams are mine, Google and other links are just links I've done the work of including so you don't have to tax yourself by typing it in using your own hands.