I wonder if it could be something to do with the fludrocortisone and the salt loss as we lose sodium in our sweat.  I found that my son used to sweat in his hair terribly, he would wake up with it wet. When we reduced his fludro dose once through puberty, the sweating stopped.  I noticed too he had cradle cap when young whereas my other children didn’t.  His hair is also thick and grows very quickly!!!