I just saw my dermatologist and scheduled to have a large mole removed because my clothes rub and irritate it. She explained to me the type of mole it is called and what causes it. It is characterized by a white center that is hard and goes deep under the skin, like a seed under the skin. But she spoke so fast, and we talked about three different moles; so I no longer remember what this kind is called or how/why it develops.