What Is The Treatment For Skin Darkening And Itching?

hi my wife used a soap and it has made her skin dark and itching for the past two years. this is around the breast, neck, shoulders,the back and on her stomach. this dark sports comes out when she is about to have her period, she was told to use HYDROCORTISONE and after the 5 use of the tube everything has come back again. what do you recommend for her as a doctor. thanks