What ingredients in neosporin can an allergic reaction?

Neosporin: Neosporin is a very common allergen, as is Bacitracin (both are very commonly used). Interestingly, neither is better than vaseline at preventing infection, but both are usually better at treating one. So, if you have a scratch, simple use of vaseline (or equivalent) is best to prevent an infection, and save the antibiotics for a proven infection. Stop using neosporin if it causes a rash for u.