Q. Hi Doctor My 2year Old Daughter Has This Thing

Q. Hi doctor my 2year old daughter has this thing that looks like an allergy but it only appears at night everyday and its ichy. during the day there is no sign of it you would swear da was nothing. i am confused as to what it is. i have been giving her allergex every night and it does not show but when i dont give her before bed it appears. is it safe to give her allergex on regular baisis daily for weeks?