A topical antifungal for athlete's foot and ringworm
Undecylenic acid
An over-the-counter topical antifungal applied to the skin to treat athlete's foot and ringworm.
What is Undecylenic acid?
Undecylenic acid is a topical antifungal applied to the skin to treat fungal infections such as athlete's foot and ringworm. It works against the fungi that cause itchy, flaky, cracked skin, often between the toes. To clear the infection it needs to be used regularly and the full course completed, even once the skin looks better, because stopping early can let it return. Keeping the area clean and dry helps it work and reduces the chance of the infection coming back.
Education and reference only. This is a plain-language guide to Undecylenic acid — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Undecylenic acid is an antifungal medicine for use on the skin, found in creams, powders and sprays for problems like athlete's foot and ringworm. It is applied directly to the affected skin rather than swallowed. It is a self-care treatment for common fungal skin infections, available from pharmacies, and is often used alongside foot-care measures to keep the skin healthy and dry.
How it works
Undecylenic acid works against the fungi that infect the outer layers of the skin, helping to stop them growing and spreading. By reducing the fungal growth, it allows the itchy, flaky, sometimes cracked or sore skin to settle and heal over the course of treatment. Powder forms also help by keeping the area dry, since fungi thrive in warm, moist conditions such as sweaty feet inside shoes. It acts where it is applied and does not treat infections deeper in the body.
Company & origin
Originated / developed by: Various (widely available).
A long-established topical antifungal used on the skin for fungal infections such as athlete's foot and ringworm. It is a familiar pharmacy treatment in the UK, sold under brands such as Mycota, in creams, powders and sprays designed to tackle and help prevent fungal skin infections on the feet.
Practical use
How to take Undecylenic acid
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Wash and dry the affected skin thoroughly, especially between the toes, before applying it.
- Apply the cream, powder or spray to the affected area as directed and to the surrounding skin.
- Keep using it for the full recommended course, continuing after the skin looks better to prevent return.
- Keep the area dry, change socks regularly and let footwear air to discourage the fungus.
- Seek advice if the infection spreads, involves the nails, or does not improve.
Weighing it up
Advantages & disadvantages of Undecylenic acid
Advantages
- Treats common fungal skin infections like athlete's foot without a prescription.
- Available in cream, powder and spray forms to suit different needs.
- Powder forms also help keep the skin dry and discourage regrowth.
Disadvantages
- Needs regular, sustained use, and stopping early often lets the infection return.
- Acts only on the skin surface and does not treat nail or deeper infections.
- May not be strong enough for severe or widespread infections.
Practical use
Good to know
The key to success is keeping the area clean and dry and completing the full course, typically continuing for a period after the skin looks normal, because stopping too soon is a common reason the infection comes back. Drying carefully between the toes, changing socks and letting shoes air all help. If the skin is badly broken, the nails are involved, the infection is spreading, or it does not improve, it is worth getting it checked, as a different or stronger treatment may be needed.
Who should not take it / use with caution
- Anyone who has previously reacted badly to undecylenic acid or a similar product.
- People needing treatment for fungal nail infection, which usually needs different treatment.
- Anyone applying it to badly broken, weeping or infected-looking skin without advice.
Monitoring
- No blood tests are needed; judge by whether the skin is healing.
- Watch the treated area for increasing irritation or a spreading rash.
- Review with a clinician if it does not improve or keeps coming back.
Side effects
- Mild skin irritation, redness or stinging where it is applied.
- Occasional itching or a burning feeling on the treated skin.
- Rarely, an allergic skin reaction with a worsening rash.
Key interactions
- Few medicine interactions, as little is absorbed through the skin.
- Avoid applying other strong topical products to the same area at the same time unless advised.
- Tell a pharmacist about other skin treatments if the infection is not clearing.
Available as: Creams, powders and sprays applied to the skin.
Answers
Undecylenic acid: frequently asked questions
How long do I need to use it?
You usually need to keep using it for the full recommended course and continue for a period after the skin looks normal. Stopping too early is a common reason athlete's foot comes back, so finishing the course matters.
Will it treat a fungal nail infection?
No, it works on fungal infections of the skin, not the nails. Nail infections sit under the nail and usually need different, often longer treatments, so see a pharmacist or doctor for those.
Why is keeping the area dry important?
Fungi thrive in warm, moist conditions such as sweaty feet inside shoes. Drying carefully between the toes, changing socks and airing footwear makes it harder for the fungus to grow and helps the treatment work.
Can I use it for ringworm elsewhere on the body?
Undecylenic acid is used for skin fungal infections including ringworm. If the patch is large, spreading or on the scalp or face, or it does not improve, get it checked as it may need a different treatment.
What if it does not clear up?
If the infection does not improve, spreads, involves the nails or keeps returning, seek advice from a pharmacist or doctor. A different or stronger antifungal may be needed.
Authoritative sources
- BNF
- NICE CKS
Building a medicines information resource?
We create evidence-led, dose-free drug and formulary references for teams.