The short version

Neosporin is a petrolatum base carrying three antibiotics: neomycin, bacitracin and polymyxin B. The petrolatum is fine. The antibiotics are the problem, and neomycin is the worst of them.

Neomycin was named the American Contact Dermatitis Society’s Contact Allergen of the Year for 2010. In North American Contact Dermatitis Group patch-test data for 2009–2010 it came in second among all allergens tested, at 8.7% prevalence, and patch-test positivity has run roughly 7.2%–13.1% across the last twenty years. It is the topical antibiotic most likely to cause contact allergy, and co-reactivity with bacitracin and polymyxin is well documented — which matters here, because all three are in the same tube.

That is a high number for something people spread on their face without a second thought.

The trap that makes it worse

Allergic contact dermatitis from neomycin shows up as redness, itching, scaling and swelling spreading out from where the ointment went. It is usually delayed — appearing a day or more after application, not immediately.

Which means it looks exactly like an infection that is getting worse.

So the intuitive response is to apply more ointment. That adds more allergen, the rash spreads further, and the whole thing reads as confirmation that the infection is winning. People can run this loop for a week before anyone suggests the tube is the cause.

The rule worth remembering: if a wound gets angrier the longer you treat it, the treatment is a suspect. Stop, and see whether it settles.

What to do instead for a clean minor wound

For an ordinary scrape, shaving nick, or picked spot that isn’t actually infected, dermatologists routinely recommend the same thing:

  1. Wash it with soap and water.
  2. Apply plain petrolatum — the unscented, single-ingredient kind.
  3. Cover it if it’s somewhere that will get knocked or dirty.

What helps a minor wound heal is keeping it moist and covered. That is the part petrolatum does, and it is the part Neosporin’s petrolatum base was doing all along. The antibiotics are along for the ride on a wound that was never infected, and they carry the allergy risk.

Plain petrolatum is also unusually well behaved for a sensitive-skin product: one ingredient, no fragrance, nothing to react to. If you reach for Aquaphor instead, note that it isn’t the same thing — it contains lanolin alcohol, which is also a recognised contact allergen, though a far less common one than neomycin. If a healing ointment seems to be making a spot angrier, plain petrolatum is the honest control experiment.

When to see a doctor

None of the above applies to a wound that is genuinely infected — spreading warmth and redness, pus, increasing pain, fever, or a red streak tracking away from the site. That needs medical attention and probably an oral antibiotic, not anything sold next to the bandages. The same goes for anything on the face near the eye, any bite from an animal, and any wound that isn’t closing.

And it is worth saying plainly: if you have already been using Neosporin on your face and the area is inflamed, the useful next step is to stop applying it and get it looked at, rather than switching to another antibiotic ointment.

Why there are no application instructions

People usually reach this page while planning to use Neosporin on a pimple, a cyst, or under a bandage. We do not give instructions for those uses. Neomycin can cause allergic contact dermatitis, clean minor wounds usually do not need a triple-antibiotic ointment, and Neosporin is not an acne treatment.

Sources

This page summarizes published guidance. For a wound you are worried about, see a doctor.