Itchy cheeks

Im not sure why but when I take off my baby's diaper and put her in the bathtub she scratches at her cheeks and back uncontrollably to the point the she will leave little cuts. Im thinking I should try switching diapers for a little while. I havent switched because this is the only time she seems to have a problem scratching. Ive tried letting her air out for like 20 min before bath and I've tried hydrocortisone before bath. Has anyone else had this happen?