I suspect it's sweet potato that cause sudden outbreak of eczema in my 7mo. I have removed it from his diet for a few days and he improved...how shld I confirm it? When can I try to introduce the suspect food again or he can't have it for life?

Wow sweet potato allergy that's quite rare. You may want to try a little again after two months and if still allergic perhaps wait till after one year old. Babies can grow out of allergies. When he is older you may want to bring him to Kkh to do allergy test https://www.kkh.com.sg/Services/Children/AllergyService/Pages/Home.aspx