What Causes Oozing Rashes On The Feet And Ankles?

My husband is 48 years old. he is 5 7 . He has had asthma since he was 2 and now takes advair and ventolin fha for it. It pretty much stays under control. since around 2000, 2003 he has had a rash like on the top of his feet and ankles. It comes and goes for no reason. He has been to a top dermatologist and has had patch tests, but no one can tell him what it is. It gets bright red,looks raw,and when its bad if hes outside and its warm, even though hes not in the sun, it will look wet and get little bumps that will ooze a light clear,yellow liquid.We have ot changed any detergents,body washes or anything. It just comes and goes for no reason.