I was in the marine corps and went to both iraq and afgan. had the problem both places, spent minimal time out of my boots. I eventually saw the doc and he explained it was common. It is from your feet being to moist from sweat and constantly being in a shoe, then when your not in shoes they get over dry. the one thing i found really helped was vasiline before i went to bed and put a sock on. morning time it was great. hope this helps