Warts can appear anywhere on your skin such as feet, knees, or hands. Even though they may seem smooth from the surface, they are thick and scaly from beneath. You can even call them bumps that go deeper into your skin. Unlike a skin tag, a wart appears due to a virus and not because of genetic or damage to your skin caused by the sun. You need to be extra careful of warts because they are contagious and can spread from one person to another. Thus, a wart on your skin can also reflect the fact that you have recently come into contact with someone suffering from them.