Medication

Nystatin

Nystatin is an antifungal that works on Candida yeast and nothing else. It does not treat athlete's foot, ringworm, or jock itch — those are dermatophytes, a completely different fungus. That mix-up is one of the most common prescribing errors in skin care.

At a Glance

Nystatin is an old, safe, and narrow antifungal. It kills Candida — the yeast behind oral thrush, diaper rash yeast infections, and the red, sore rashes that develop in skin folds — and it has essentially no effect on dermatophytes, the fungi that cause athlete's foot, ringworm, and jock itch. Applied to skin or swished in the mouth it is barely absorbed into the body, which makes it exceptionally safe, including in babies. Getting the right fungus is the whole game with this drug.

Key Facts

AKA	Nystop, Nyamyc, Mycostatin (cream, ointment, powder, and oral liquid)
Drug Class	Polyene antifungal — active against Candida only
Rx or OTC	Prescription only in the US
Typical Strength	100,000 units per gram in topical cream, ointment, and powder; 100,000 units per mL as an oral liquid
Time to Work	Improvement in a few days; treatment continues until healing is complete
Evidence Level	Long-established and reliable for Candida. No activity against dermatophytes, bacteria, or viruses
Important	It does nothing for athlete's foot, ringworm, or jock itch.

How It Works

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Nystatin binds to ergosterol, a fat molecule that sits in the membrane of yeast cells. Once bound, it punches holes in the membrane, and the contents of the cell leak out. Human cells use cholesterol rather than ergosterol in their membranes, so they are largely spared.

It is not absorbed through intact skin or through the lining of the mouth or gut in any meaningful amount. Swallowed, it works inside the gut and passes straight out. That is why a drug that would be quite toxic in the bloodstream is completely safe as a cream or a mouth rinse.

And it only works on yeast. The label is specific: it treats infections caused by Candida albicans and other susceptible Candida species, and it has no appreciable activity against bacteria, protozoa, or viruses. Dermatophytes — the Trichophyton and Epidermophyton species that cause ringworm and athlete's foot — are not covered either. Nystatin on a case of athlete's foot does nothing at all, and the weeks spent finding that out are the real cost.

What It Treats

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Intertrigo

Strong evidence

Nystatin is highly effective against Candida and has no activity against dermatophytes. That makes it a targeted choice once a KOH scraping has confirmed yeast.

Who It's For & Who It's Not

Who it's for

Babies and adults with oral thrush — white patches in the mouth from Candida.

Diaper rash where yeast has taken hold, which typically looks beefy red with smaller spots scattered just outside the main patch.

Yeast in skin folds — under the breasts, in the groin, under the belly, between the buttocks. This overlaps with intertrigo, which is often part friction and part yeast.

Yeast at the corners of the mouth, or under the edge of a fingernail in someone whose hands are wet all day.

People who need something extremely safe — newborns, pregnancy, the very elderly.

Who it's not for

Athlete's foot, ringworm, jock itch, or scalp ringworm. Nystatin does not touch dermatophytes. Use terbinafine cream, clotrimazole, or luliconazole instead.

Nail fungus, whether yeast or dermatophyte. It will not cross a nail plate.

Tinea versicolor and fungal acne. Those are caused by Malassezia, another yeast that nystatin does not reliably cover.

Vaginal yeast infections in the US, where azoles are standard.

Anyone with a Candida infection that has spread into the bloodstream. Topical and oral nystatin do not get absorbed, so they cannot treat internal infection.

How to Take It

How to use it on skin

Apply liberally to the affected area two or three times a day, and continue until the skin has healed completely — usually a few days past the point where it looks normal. Powder can be dusted on damp areas two or three times a day. This is educational only; follow your prescriber's directions.

Keep the area dry, or the cream will not win

Candida thrives in warm, damp, closed skin. Treating a skin-fold yeast infection while the fold stays wet is a losing battle. Dry properly after washing, including with a cool hair dryer on a low setting. Use a soft cloth or absorbent material to keep opposing skin surfaces apart. Loose, breathable clothing. Powder in the folds. Managing moisture is at least half the treatment.

For oral thrush

The liquid is swished around the mouth and held there as long as possible before swallowing, usually four times a day. Getting contact time is the point — swallowing it quickly wastes it. For babies, the dose is divided and painted into each cheek with a dropper or a clean finger.
If a baby has thrush and is breastfeeding, the mother's nipples usually need treating at the same time, or the two simply keep reinfecting each other.

What to Avoid

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There are no drug interactions to worry about, because nystatin is not absorbed. It is safe alongside almost anything, and safe in pregnancy and breastfeeding.

Using it on the wrong fungus

Repeating this because it is the point of the page: nystatin does nothing for athlete's foot, ringworm, or jock itch.

Airtight coverings

, including tight plastic pants over a diaper, which trap the moisture the yeast is living on.

Reaching for a nystatin-plus-steroid combination out of habit

The steroid can thin skin in folds, where skin is already thin, and it masks what is going on.

Eyes

Not for ophthalmic use.

Side Effects

One of the best-tolerated drugs in dermatology. Reactions are reported in well under one percent of people.

Common and expected

Mild burning, stinging, or itching where it is applied.
With the oral liquid: an unpleasant taste, occasional nausea, and sometimes diarrhea at higher doses.

Tell your doctor

A rash that gets redder or itchier during treatment — occasionally people become allergic to nystatin itself.
A rash that has not improved at all after about a week. That usually means it is not yeast, and the diagnosis needs revisiting.
Skin in a fold that becomes painful, weeping, or foul-smelling, which suggests a bacterial infection on top.

Stop and get care

Swelling of the face, lips, or tongue, hives, or trouble breathing. Very rare, but reported.
Widespread blistering or peeling of the skin.

How Long Until It Works

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Soreness and itching usually ease within two to three days, and skin infections clear over about one to two weeks.

Oral thrush generally improves in a few days, but treatment should carry on for around 48 hours past the point where the mouth looks clear, or it comes straight back.

If there is no change at all after a week, the most likely explanation is that this is not Candida. That is the moment to reconsider the diagnosis rather than to keep applying.

What Happens When You Stop

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Once the yeast is cleared, it stays cleared as long as the conditions that let it grow are dealt with.

Relapse is common where those conditions persist: a skin fold that stays damp, poorly controlled blood sugar, an inhaled steroid used without rinsing afterward, a breastfeeding pair where only one side was treated, or a course of antibiotics. Nystatin cures the episode. It does not change the reason the episode happened.

If yeast keeps coming back in the same fold, moisture management — drying, separating skin surfaces, breathable fabrics, powder — usually does more over the long run than another tube of cream.

Who should not take it+

Do not use it if you are allergic to nystatin.

Do not use it in the eyes.

Topical and oral nystatin are not treatments for infection that has spread into the bloodstream, because the drug is not absorbed.

It is considered safe in pregnancy, in breastfeeding, and in newborns.

FAQ+

Will nystatin cure athlete's foot?No. This is the single most consequential misunderstanding about this drug. Athlete's foot, ringworm, and jock itch are caused by dermatophytes, and nystatin has no activity against them. You need terbinafine cream, clotrimazole, or a similar drug.

How do I know whether my rash is yeast or ringworm?Yeast tends to sit in warm damp folds, looks beefy red and shiny, and often has small separate spots just outside the main patch. Ringworm tends to form a ring with a raised scaly edge and a clearer center, and it appears on exposed skin rather than in folds. Neither rule is perfect. A skin scraping settles it, and it is worth asking for when a rash is not behaving.

Why was I given nystatin with a steroid in it?Combination products are prescribed very commonly. The steroid reduces itch quickly, which patients like — but it also masks the picture, and if the rash is actually a dermatophyte it makes things worse. Plain nystatin is usually the better choice for a confirmed yeast rash in a fold, where the skin is thin.

Is it safe for babies?Yes. It is one of the standard treatments for infant thrush and yeast diaper rash, and it is barely absorbed.

Does swallowing it treat a yeast infection elsewhere in my body?No. Oral nystatin works inside the gut only. It is not absorbed, so it cannot treat a vaginal, skin, or bloodstream infection.

Can it treat a vaginal yeast infection?Nystatin vaginal preparations exist in some countries, but in the US the standard treatments are azoles like fluconazole, miconazole, or clotrimazole.

How long should I keep using it?Until the skin has healed completely, and a couple of days beyond that. For oral thrush, about 48 hours past the point where the mouth looks normal.

What if it is not working?After about a week with no change, assume the diagnosis is wrong before assuming the drug is. In practice the rash is usually a dermatophyte infection, eczema, psoriasis, or plain friction intertrigo.

Does it work on nail fungus?No. It cannot penetrate a nail plate, and most nail infections are dermatophytes anyway.