Human papillomaviruses can live on healthy skin without causing infection. But when a human papillomavirus enters the body through small breaks in the skin, it can infect the skin cells beneath the surface, causing a wart to grow.
A wart can take many months to grow before it becomes visible.
Warts, particularly newer ones, are easily spread. They can spread to other parts of the body or to other people.
Plantar warts can be pushed beneath the skin's surface by pressure from standing and walking. A thickening of the skin slowly forms over most of the wart and looks and feels like a callus.