What could this sore be?

[Mecra7]

My husband has a bump on the bottom of his foot that started out as a small, pin like white spot in the skin of his foot. He has smooth, soft feet that sometimes sweats when he's at work, but never with a smell and are well taken care of when he is at home. He thought that there was a hair stuck in his foot because his skin is so soft, his hairs are like needles to his skin. There was no hair there, just this pin like, small, white mass. After he attempted to get the hair he saw in it out, he found out that there was no hair that was causing him pain and the mass grew bigger. Now it is the size of a double AA battery top and has a black dot or so in the middle. It reminds me of warts, especially since his feet and hands always sweats, but I am not sure. We don't have insurance yet because they are all too expensive for us right now. Does anyone have an idea of what this could be? (I wish that this site allowed pictures so that I could show it) It is causing him a lot of pain now, to the point that he limps when walking.