How do you know if it's an allergic reaction?

[melon1]

DD has eczema which is pretty much under control at the moment -when it started at 2 months she did have some on her face but that cleared up pretty quickly and she hasn't had any there for months - recently she's started to develop a red rash round her mouth when she eats anything tomatoey - could this be the eczema? Teething? The eczema on her body hasn't flated up, just around her mouth - is this an allergic reaction or just sensitive skin?

sorry had to dash away earlier but wanted to reply. The short answer is its really hard (see post about husband and egg ) Try putting tomato on her arm or back to see if that goes red, if it does its probably allergy. Tomatoes are quite a common allergen. You need skin prick and blood tests to be sure.