Oatmeal allergies are rare. Your child may be "sensitive" oatmeal.
My neighbor delt with the same when her son was 7 months. She kept trying it and he actually had stonger reactions closer to 12 months so after tests and some scary moments finally quit giving him oatmeal for a year. Now he is almost three and eats all foods without showing signs of any allergies.
My kids have food allergies and we have tried to "listen" to what their bodies are telling you. The fine red rash has indicated, to me, that they aren't ready for it. Maybe try it again in a few months.
Lots of people will tell you, "Oh, I started mine on strawberries and peanut butter at 12 months and they were JUST FINE" and blah-blah ...blah.
Great for them! Your baby's body is letting you know that you need to err or the side of caution.
Dr. Zora at Atlanta Asthma & Allergy, in Alpharetta, is great if it gets to that point.