Originally Posted by paperclippy
When he talked to them on the phone yesterday they thought it might just be a heat rash and said keep an eye on it -- steroids are often used to treat rashes so it shouldn't be a reaction to the steroids. I told DH to take the toothpaste along to the doctor in case there is some ingredient in it that is common for allergies. It could also be from whatever virus caused her croup in the first place, because A doesn't have it. The croup seems about the same as before.
There are people who react to cortisone, and the symptoms are usually skin symptoms. It's rare but not unheard of. You can check it out on WebMD or other medical sites. It would be unusual for one twin to be allergic to the toothpaste and the other not--or are you only using it for one?