Neosporin Original Ointment contains three antibiotics: bacitracin zinc (400 units per gram), neomycin sulfate (3.5 mg per gram), and polymyxin B sulfate (5,000 units per gram). These three ingredients are blended into a petroleum-based ointment that keeps the antibiotics in contact with the wound. Each one targets bacteria in a different way, which is why the combination works against a broad range of common skin infections.
The Three Active Antibiotics
The reason Neosporin uses three separate antibiotics instead of one comes down to coverage. Different antibiotics kill different families of bacteria, and minor cuts and scrapes can be contaminated by several types at once. By combining all three, the ointment covers most of the bacteria you’d encounter in everyday wounds.
Bacitracin zinc handles the majority of gram-positive bacteria, the family that includes Staphylococcus aureus (staph), one of the most common causes of skin infections. It works by interfering with the way bacteria build their cell walls. Without a functional wall, the bacteria can’t survive or reproduce. Bacitracin also has some activity against Haemophilus influenzae and certain Neisseria species.
Neomycin sulfate belongs to a class of antibiotics called aminoglycosides. It kills bacteria by disrupting their ability to make proteins. Bacteria depend on protein production for virtually every function, so shutting that process down is lethal. Neomycin is particularly effective against gram-negative bacteria, including E. coli and Klebsiella-Enterobacter species.
Polymyxin B sulfate takes a completely different approach. It binds to the outer membrane of gram-negative bacteria and punches holes in it, essentially acting like a detergent that dissolves the membrane’s structure. This makes it effective against organisms like Pseudomonas aeruginosa, a bacterium notorious for infecting wounds, especially in moist environments.
Together, the three antibiotics are considered active against Staphylococcus aureus, E. coli, Haemophilus influenzae, Klebsiella-Enterobacter species, Neisseria species, and Pseudomonas aeruginosa. That list covers the bacteria most likely to colonize a minor wound.
The Ointment Base
The antibiotics make up only a tiny fraction of the tube’s contents by weight. The bulk of Neosporin is its inactive base: a blend of petroleum-derived ingredients (including white petrolatum and mineral oil) that give the ointment its thick, greasy texture. This base serves two purposes. First, it keeps the active ingredients stable and evenly distributed so each application delivers a consistent dose. Second, it forms a moisture barrier over the wound, which helps prevent the cut from drying out and cracking. Moist wounds generally heal faster than dry ones, so the base itself contributes to recovery even apart from the antibiotics.
The petroleum base is also what gives Neosporin its long shelf life. The ointment should be stored between 68°F and 77°F (20°C to 25°C). You’ll find an expiration date printed on the packaging, and it’s worth checking before applying an old tube, because the antibiotics lose potency over time.
How It Differs From Pain Relief Versions
Neosporin sells several product variations beyond the original ointment. The most popular alternative is Neosporin + Pain Relief, which adds a topical numbing agent called pramoxine hydrochloride at a concentration of 10 mg per gram. Pramoxine works by temporarily blocking nerve signals at the skin’s surface, reducing the sting and soreness around a fresh cut. The three core antibiotics remain the same across all versions; the pain relief line simply layers on an analgesic.
There’s also an important format difference. The original comes as an ointment (greasy, petroleum-based), while the pain relief version is available as a cream (lighter, water-based, and easier to wash off). Creams absorb more quickly but don’t create the same occlusive moisture barrier that the ointment does.
Neomycin Allergies Are Common
One ingredient worth knowing about is neomycin, because it’s a relatively common cause of contact allergies. A large meta-analysis covering over 456,000 patch-tested adults found that roughly 3.2% had a contact allergy to neomycin. Among children, the rate was even higher at about 4.3%. That makes neomycin one of the more frequently flagged allergens in dermatology patch testing.
If you apply Neosporin and notice increasing redness, itching, or a rash that spreads beyond the wound’s edges, that’s more likely an allergic reaction to the neomycin than a worsening infection. The two can look similar at first glance, but an allergy tends to cause itchy, bumpy skin in a pattern matching where the ointment was applied, while an infection usually brings warmth, swelling, and sometimes pus. People who know they’re sensitive to neomycin can use alternatives that contain only bacitracin, or bacitracin combined with polymyxin B, skipping the neomycin entirely.
What Neosporin Does Not Cover
All three antibiotics in Neosporin target bacteria. The ointment has no effect on viruses, fungi, or deeper tissue infections. It’s designed for minor surface wounds: small cuts, scrapes, and burns where the goal is to prevent bacteria on the skin from colonizing the damaged tissue. Wounds that are deep, punctured, heavily contaminated, or already showing signs of infection (spreading redness, fever, red streaks moving away from the wound) need more than a topical ointment. Neosporin also won’t help with surgical wounds or animal bites, which carry infection risks that go well beyond what a surface antibiotic can manage.