A wart isn’t just a bump sitting on top of your skin. Beneath the surface, it’s a mass of thickened, virus-altered skin cells that can extend several millimeters deep, with its own blood supply visible as tiny black dots. What you see on the outside is only part of the story, especially with plantar warts on the feet, which Cleveland Clinic compares to an iceberg because so much of their bulk is hidden below.
How a Wart Grows Into the Skin
Warts are caused by human papillomavirus (HPV), which infects the deepest living layer of the skin called the basal layer. The virus enters through tiny cuts or breaks, and once inside, it hijacks the normal skin cell machinery. An infected cell produces roughly 50 to 100 copies of the virus, and as these cells divide, one stays anchored in that deep layer while others push upward. This is why warts keep coming back if treatment only removes the surface: the virus-producing factory sits at the base.
As infected cells rise toward the skin’s surface and mature, the virus ramps up production dramatically, generating thousands of copies per cell. Along the way, it forces the cells to multiply faster than normal and resist the body’s usual signals to die off. The result is a column of excess tissue that bulges outward and, depending on location, also grows inward.
What the Inside of a Wart Looks Like
If you could slice a wart in half and look at it under a microscope, you’d see a structure very different from normal skin. The outer layer is dramatically thickened, with finger-like projections pushing upward. These projections give common warts their characteristic rough, cauliflower-like texture on the surface. Beneath that, the middle layers of skin are also abnormally thick, stacked in tiers rather than the smooth, orderly layers of healthy skin.
Woven through this overgrown tissue are tiny blood vessels, capillaries that the wart recruits to feed its rapid cell growth. These capillaries often become clotted, and that’s what creates the small black or dark red dots you can sometimes see when you look closely at a wart’s surface. Many people mistake these for “seeds,” but they’re actually thrombosed (clotted) capillaries. If you were to pare down a wart layer by layer, these dark pinpoints become more visible as you get closer to the core. When nicked, they bleed readily.
How Deep Warts Actually Go
Common warts on the hands and fingers typically range from 2 to 10 millimeters wide, roughly the size of a pencil eraser or smaller. Their depth is usually limited to the outer skin layer (the epidermis), which is only about 1 to 2 millimeters thick on most of the body. The virus doesn’t invade deeper tissues like muscle or fat. So while a wart can feel like it has “roots,” what you’re actually feeling is densely packed, abnormal skin tissue.
Plantar warts are the exception in terms of perceived depth. Because they grow on the sole of the foot, your body weight pushes them inward rather than letting them protrude outward. This creates a wart that extends deeper into the skin, sometimes causing significant pain when you walk. The tissue itself is still confined to the outer skin layers, but the inward growth pattern means there’s more hidden bulk beneath the surface than what’s visible. After removal, plantar warts can leave a noticeable hole where the compressed tissue used to be, which gradually fills in with normal skin over time.
How to Tell a Wart From a Callus
One of the most reliable ways to identify a wart beneath the skin, especially on the feet, is to look at your skin lines. The natural fingerprint-like ridges on your palms and soles (called dermatoglyphics) are interrupted by warts. The lines stop at the edge of the wart and pick up again on the other side. A callus, by contrast, preserves these lines completely. In one study examining 30 wart cases, interrupted skin lines were present in 100% of them, making this one of the most consistent diagnostic markers.
The other telltale sign is those black dots. Calluses and corns don’t have their own blood supply the way warts do, so they never show the dark pinpoints. If you gently pare the surface of a suspicious bump and see tiny dark spots or minor bleeding, it’s almost certainly a wart.
Mosaic Warts and Cluster Growth
Sometimes warts don’t grow as isolated bumps. Mosaic warts are clusters of plantar warts that merge together on the sole of the foot, forming a larger patch that can be an inch or more across. Beneath the surface, each individual wart in the cluster has its own blood supply and its own core of virus-infected tissue. Because they grow deeply into the skin and cover a wider area, mosaic warts tend to be more painful and harder to treat than a single wart.
What a Dying Wart Looks Like
If you’re treating a wart and wondering what’s happening below the surface, there are visible signs of progress. As treatment kills the infected tissue, the wart begins to shrink and the surface starts peeling. The skin over and around the wart turns white, especially after soaking, which indicates dead tissue that can be filed away with a pumice stone or emery board.
With freezing treatments, a blister forms underneath the wart, physically lifting the infected tissue away from the healthy skin below. This blister typically flattens within two to three days, and the dead wart tissue falls off within two to three weeks. Some topical treatments work similarly by creating a blister that pushes the wart upward until it separates.
After the wart falls off, the skin underneath may look lighter than the surrounding area. This color difference can take several months to fade, and in some cases it’s permanent. With deeper plantar warts, you may notice a small indentation or hole where the wart’s bulk used to sit below the surface. Normal skin growth gradually fills this in, though it can take weeks to months depending on how deep the wart extended.