Oral thrush is a fungal infection inside the mouth. It is common in people who wear dentures, use inhalers, or have a weakened immune system — and it is treatable.
Oral thrush (also called oral candidiasis) is an infection of the mouth caused by a fungus called Candida albicans. This fungus is naturally present in the mouth in small amounts, but under certain conditions it can multiply and cause an infection.
It can affect people of any age, but is most common in:
Babies and young children
Older adults, especially those who wear dentures
People with a weakened immune system
People taking inhaled corticosteroids (such as inhalers for asthma)
People with dry mouth
People taking long-term antibiotics
Oral thrush is not contagious in healthy adults through normal contact, and it is not a sexually transmitted infection.
What causes oral thrush?
Certain conditions allow Candida to overgrow:
Steroid inhalers — inhaled steroids (used for asthma or COPD) can leave steroid residue in the mouth, encouraging fungal growth. Rinsing your mouth with water after using an inhaler greatly reduces this risk.
Antibiotics — these kill helpful bacteria in the mouth that normally keep Candida in check.
Dry mouth — saliva has antifungal properties; reduced saliva flow allows Candida to thrive.
Dentures — especially if not cleaned properly or worn during sleep. Ill-fitting dentures trap the fungus under the plate.
Weakened immune system — due to conditions such as HIV, diabetes, cancer treatment, or long-term steroid use.
Smoking — alters the mouth environment and increases risk.
Signs and symptoms
Oral thrush can look and feel different depending on the type and severity:
White or cream-coloured patches on the tongue, inside the cheeks, roof of the mouth, or throat. These patches can often be wiped off, leaving a red or bleeding surface underneath.
Redness and soreness in the mouth — often underneath dentures (called denture stomatitis)
A burning or sore sensation in the mouth or throat
An unpleasant taste or altered taste
Cracking and redness at the corners of the mouth (angular cheilitis — often associated with thrush)
Difficulty eating or swallowing in more severe cases
How is oral thrush treated?
Oral thrush is very treatable. Your dentist or doctor will usually prescribe an antifungal medicine:
Miconazole oral gel — an antifungal gel applied directly in the mouth. It is the most commonly prescribed first-line treatment. Apply with a clean finger after meals, and keep it in contact with the affected area as long as possible before swallowing. Important: miconazole interacts significantly with warfarin (a blood-thinning medication) and can increase bleeding risk. Tell your dentist or doctor if you take warfarin or any anticoagulant before being prescribed miconazole.
Nystatin suspension — an antifungal liquid held in the mouth and swallowed. Preferred when miconazole cannot be used — for example in patients taking warfarin or certain other medicines.
Fluconazole tablets — a systemic antifungal taken by mouth, used for more severe or persistent infections.
It is important to complete the full course of treatment even if symptoms improve quickly. Stopping early can allow the infection to return.
What you can do at home
Good oral hygiene and simple precautions can prevent thrush from recurring:
Rinse your mouth with water and spit out after using a steroid inhaler every time — this is highly effective at preventing inhaler-related thrush. Using a spacer device with your inhaler also significantly reduces the amount of steroid deposited in the mouth and throat; ask your GP or asthma nurse about this.
If you wear dentures: remove them at night, clean them thoroughly with a denture brush and denture cleaner, and soak them overnight in a denture cleaning solution. Do not sleep in your dentures.
Clean your tongue gently when brushing your teeth.
Avoid sugary foods and drinks — Candida thrives on sugar.
Stay hydrated — good saliva production helps prevent overgrowth.
If you have a dry mouth, ask your dentist about dry mouth products that contain antifungal agents.
When to see your dentist or doctor
See your dentist or doctor if:
You have white patches in your mouth that have not resolved within 2 weeks with treatment, or that keep recurring
You are unsure whether the patches are thrush — not all white patches in the mouth are thrush, and some require further investigation
The infection is spreading or you are having difficulty swallowing
You are in a high-risk group (immunocompromised, uncontrolled diabetes) and develop symptoms
Important: A white patch in the mouth that does not wipe off, does not clear with antifungal treatment, and persists beyond 3 weeks must always be assessed by a dental or medical professional — it is not likely to be thrush and requires further investigation.
This leaflet is for general information only and does not replace professional dental advice. Your dentist will discuss your individual circumstances and any risks and treatment specific to you. Treatment outcomes vary between patients depending on individual circumstances.
References
Aligned with guidance from: NICE, SDCEP, FGDP(UK).