I have the same thing happening... although mine itch! It starts out as a small blister under the skin, filled with clear fluid sometimes a bit of blood. I went to my regular Dr. and he said its a skin fungus. My podiatrist confirmed it also. He told me to rub a anti-fungal cream on it twice a day. I am using a generic product similar to lotrimin. Mine seem to be clearing up now. You need to find a way to keep his feet dry, that will help.