Hello. I m Dr. Christensen. I m sorry your son is uncomfortable. The rash on his groin is likely due to a yeast infection, which could actually worsen if you treat it with a corticosteroid cream like Cortic-DS. (Corticosteroids reduce the local immune response in your skin, which is good for allergic rashes or contact dermatitis; however, such immune suppression can allow a fungus to grow more rapidly.) In addition, using a corticosteroid on certain areas (eyelids or genitals, for example) for more than a week or so can lead to skin thinning. I d suggest you have your doctor take a look at your son s new rash to determine its cause. In the meantime, try an antifungal cream, such as terbinafine or clotrimazole. Good luck!