Neomycin Sulfate
A first-aid-ointment antibiotic that's a top contact allergen — the classic "the wound won't heal" reaction
INCINeomycin Sulfate
- Category
- Antibiotic
- Risk level
- medium
- What it is
- An aminoglycoside topical antibiotic; a component of "triple antibiotic" (with bacitracin + polymyxin)
- How common
- Among the most frequent contact allergens — ACDS "Allergen of the Year" 2010
- Cross-reaction
- Other aminoglycosides — gentamicin, tobramycin, kanamycin
- The classic clue
- "Paradoxical" worsening — a treated wound gets redder/itchier instead of healing
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This ingredient may appear under any of these names:
Commonly found in
Possible reactions
- A wound/rash that worsens or won't heal where the ointment is applied
- Redness, swelling, itching at the application site
- Delayed reaction 24–72 hours after use
- Eyelid/periorbital dermatitis from eye drops
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What is neomycin?
Neomycin sulfate is an aminoglycoside antibiotic used topically to prevent or treat bacterial skin infection. It's in OTC triple-antibiotic ointments (with bacitracin and polymyxin B), prescription topical preparations, and some eye and ear drops. It's effective — but it has a notable downside: it's one of the most common causes of allergic contact dermatitis among topical drugs, named the American Contact Dermatitis Society's "Allergen of the Year" in 2010.
Why it causes reactions — the "paradoxical" wound
Neomycin causes Type IV delayed hypersensitivity (24–72 hours after exposure), and its signature presentation is genuinely counterintuitive:
Someone puts antibiotic ointment on a cut or scrape. Instead of healing, the wound and the skin around it get redder, itchier, and more swollen. Assuming infection, they apply more ointment — which worsens the allergic reaction.
This paradoxical worsening — a "treated" wound that won't settle — is the classic clue to neomycin allergy. Because people think of it as "medicine," not a cosmetic, the allergy is often overlooked.
Neomycin also cross-reacts with other aminoglycosides (gentamicin, tobramycin, kanamycin), so a neomycin allergy means avoiding those too — including in eye/ear drops.
How to spot and avoid it
- Read first-aid labels for Neomycin / Neomycin Sulfate (and remember triple-antibiotic ointments contain it).
- Suspect allergy when a treated wound worsens rather than heals.
- Avoid the aminoglycoside family if sensitised — and tell your doctor before eye/ear drops.
- Patch test to confirm and identify cross-reactors.
Safer alternatives
- Plain petrolatum for simple minor wounds — heals as well as antibiotic ointment, no sensitisation.
- Mupirocin — a different class, no neomycin cross-reactivity (prescription).
- Genuine infections: see a clinician for a non-aminoglycoside antibiotic.
- Note bacitracin (often in the same ointment) is also a common allergen.
The bottom line
Neomycin is an effective topical antibiotic and, simultaneously, a leading contact allergen whose tell is a wound that worsens instead of healing. Most minor cuts don't need it at all — plain petrolatum is a safer default — and if you're sensitised, avoid the whole aminoglycoside family and flag it to your doctor.
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