Hello.Psoriasis is a possible diagnose to consider.There are different types of psoriasis,one of them is inverse psoriasis.Inverse psoriasis, the lesions occurs in large folds:gluteal cleft,inguinal,under the breast,armpits.Initially Lesions have your husband are not in those places. Is very important confirm or exclude diagnose of psoriasis.Psoriasis diagnose is established,in many cases,only by symptoms and exploration.It is sometimes necessary additional test such as dermoscopy and biopsy. Now prednisona is correct treatment.Improve skin lesions probably, but the most important is establish diagnose. If confirmed psoriasis,you must know that is cronic patholgy but there are very effective treatments to treat presently. I wish you good health (In case the answer would have been useful please indicate this)