What are the white patches appearing on my wifes skin?

My wife just showed me her hands and arms and the white patches that are appearing on them. My wife is a retired nurse and she tells me the patches are the results of an overactive immune system and the patches are extra skin cells, produced by her body. She has an appointment with her doctor. Question: Is this a normal function of the human body? If so, is there a medication available to correct her overactive immune system and is this a dangerous situation?