Teething rash or food allergy rash - how do you tell?

[cardamomginger]

I have started weaning dd, who is just over 5 months. We've been going through single vegetables and fruits, steamed and pureed, giving 1 new food a day for 2 days before moving to the next one. So far so good. I think. But I know we need to watch for signs of allergic reaction and that one of these is a rash round the mouth. DD is already CMP allergic and I have quite a lot of food allergies, so this is something we need to watch for. But we think she is starting to teethe (lots of dribbling, red cheeks on occasion, lots of chewing on things, but grizzly sometimes) and she gets an intermittent rash round her mouth, we think because of all the dribbling. So if we need to watch for mouth rash as a sign of allergy, but she sometimes gets a rash related to teething (and she gets a bit of eczema round her mouth sometimes too), how do we know what's what? What's the difference? I am confused! Help!

DD1 used to get a rash around her mouth from dribbling when teething. I started putting a thin layer of Vaseline around her mouth to act as a barrier and protect her skin. It worked but I don't know if that would tell you reliably whether the dribble or the food caused the reaction in the first place.

thanks! i'm starting to think it's more likely to be teething/her sporadic eczema. but it's hard to be sure!