This is classically pitted keratolysis. It's a bacterial infection due to prolonged closure and occlusion of feet with foot wear. I would advise you to clean feet daily after getting back home with Luke warm water, dry it and apply antibiotic +/- keratolytic ointment . prescription for these may be obtained from a dermatologist near you. Also make it a point to change your socks daily and also exposure your shoes to sunlight on weekends so that they get sufficiently aerated and don't colonize and organisms. Hope this helps. Warm regards.