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