What could  cause an allergic reaction making my daughters face swell and turn bright red? it starts around her mouth and spreads to her entire face.  It swells to the point that her lips will crack.  We apply ice packs and give benadryl but once it starts there is no stopping it.  The swelling lasts around two days and the redness will last a week or more. after about three days,  any affected skin will begin to peel like a healing sunburn.  We have seen three doctors (including an allergist) they say "Contact Dermatitis"  but have no idea what the irritant could be. They say to treat her with hydrocortisone cream and cold compresses.  Also, to use vaseline on her lips. Maybe someone has had a similar experience or has heard of one and could give me some clues.  My daughter is a nail biter, thus making it nearly impossible to pinpoint what exactly could be going into her mouth.  I would appreciate any help i can get.  I just can't figure this out.

Summarized question: What triggers allergic reactions with facial swelling and redness?