Oral thrush — causes and treatment
Reviewed by the My London Pharmacy clinical team, Yvonne Lim, Pharmacist Independent Prescriber
·29 July 2026
·7 min read
Quick answer
Oral thrush is a common fungal infection of the mouth caused by an overgrowth of Candida yeast. It can cause white patches, soreness and an altered taste. It is usually treated with antifungal drops or gel, and sometimes tablets. A clinician can advise on treatment and look at why it developed if it keeps returning.
What oral thrush is
Oral thrush is an infection in the mouth caused by an overgrowth of a yeast called Candida. Small amounts of this yeast live harmlessly in the mouth for many people, kept in balance by the immune system and the natural bacteria present. Thrush develops when that balance is upset and the yeast multiplies more than usual, which is why it often follows something that disturbs the mouth's normal environment rather than appearing out of the blue.
It is not usually a sign of poor hygiene and is common in babies, older adults and people with certain health conditions. In most cases it responds well to treatment, and understanding what allowed it to develop is often just as important as clearing the current episode, because it helps prevent the infection from returning.
How to recognise oral thrush
The signs of oral thrush can include:
- White or creamy patches on the tongue, inner cheeks or roof of the mouth that may rub off
- Redness or soreness inside the mouth
- A cottony feeling or loss of taste
- Cracking at the corners of the mouth
- Discomfort when eating or swallowing
When the white patches are wiped away, the area underneath may look red and slightly sore. In babies, thrush may appear as white patches that do not wipe away easily and can make feeding uncomfortable, sometimes causing them to be unsettled during feeds. Not everyone has obvious patches; for some people a persistently sore or reddened mouth, an altered or metallic taste, or a burning sensation is the main clue, and this form can be easy to mistake for other mouth problems, which is one reason it is worth having it checked if it does not settle.
What makes it more likely
Several factors can disturb the natural balance in the mouth and make thrush more likely. These include:
- Taking a course of antibiotics, which can reduce the protective bacteria that normally keep yeast in check
- Using a steroid inhaler without rinsing the mouth afterwards
- Wearing dentures, particularly if they do not fit well or are not cleaned regularly
- A dry mouth, smoking, or diabetes that is not well controlled
- A weakened immune system, or being at the very young or older end of life
Recognising a contributing factor often helps both treatment and prevention. Rinsing the mouth after using a steroid inhaler, using a spacer where appropriate, keeping diabetes well managed and good denture care can all lower the risk of thrush returning. Often more than one factor is involved at once, so it is worth looking at the whole picture rather than a single cause.
How oral thrush is treated
Oral thrush is treated with antifungal medicines applied directly in the mouth. A clinician may suggest Nystan Drop, an antifungal suspension that is held in the mouth so that it reaches the affected areas before being swallowed, used over a course of several days. It is usually given after food, and it helps to keep it in contact with the affected areas for as long as possible rather than eating or drinking straight away.
Where thrush is more extensive, persistent, or affects people who are more vulnerable, an antifungal taken by mouth that works throughout the body, such as Fluconazole 150mg Thrush Capsule, may be considered after assessment. Alongside treatment, keeping the mouth clean, cleaning dentures thoroughly and addressing any underlying factor all support recovery. It is important to complete the full course even once symptoms improve, because stopping early can allow the infection to return before it has fully cleared.
Oral thrush in babies and denture wearers
Oral thrush is common in babies, where it can appear as white patches inside the mouth that do not wipe away easily and may make feeding uncomfortable. In breastfeeding, thrush can sometimes pass between a baby's mouth and the mother's nipples, causing soreness, so both may need treating at the same time to stop it passing back and forth. A clinician, pharmacist or health visitor can advise on suitable treatment for a baby, which differs from that used in adults.
Denture wearers are also more prone to thrush, particularly where dentures do not fit well or are not cleaned properly, because the covered surfaces can allow yeast to build up. Removing dentures overnight, cleaning them thoroughly each day, and having the fit checked all help clear an episode and reduce the chance of it returning. Treating the mouth without also caring for the dentures often allows thrush to come straight back.
Reducing the risk of thrush
A few simple habits can lower the chance of oral thrush developing or coming back. Rinsing your mouth with water after using a steroid inhaler, and brushing your teeth twice a day, help keep the mouth healthy. Spitting out rather than rinsing after brushing keeps a little protective fluoride in place, and regular dental check-ups help spot problems early.
If you wear dentures, removing them at night, cleaning them thoroughly and making sure they fit well all reduce the risk. Staying well hydrated to avoid a dry mouth, not smoking, and keeping any condition such as diabetes well managed also make thrush less likely. These steps are especially worthwhile for anyone who has had thrush more than once.
What to expect from treatment
With treatment, oral thrush usually starts to improve within a few days, and the white patches and soreness settle over the course of about a week to ten days, though this varies from person to person. Sticking to the full course, even after the mouth feels better, gives the best chance of clearing the yeast completely and reduces the likelihood of an early return.
If there is little improvement after finishing a course of treatment, or symptoms come back soon afterwards, it is worth going back to a clinician rather than simply repeating the same approach. This allows the diagnosis to be confirmed, any contributing factor to be addressed, and a different or longer treatment to be considered where needed.
Recurrent or persistent thrush
If oral thrush keeps coming back or does not clear with treatment, it is worth looking more closely at why. Recurrent thrush can be linked to factors such as inhaler technique, denture fit, a dry mouth or an underlying condition like diabetes.
A clinician can help identify and manage any contributing cause, which is often the key to preventing repeated episodes rather than treating each one in isolation. In some cases, further checks may be suggested to understand why the infection keeps returning, so that the underlying reason, not just the symptoms, is addressed.
Repeated episodes can be frustrating, but they usually have a manageable explanation once looked at properly. For example, adjusting inhaler technique or adding a spacer, having a denture reline or replacement, treating a dry mouth, or improving control of diabetes can each make a real difference to how often thrush returns. Tackling the cause alongside each course of treatment tends to be far more effective than treating episode after episode on its own.
When to seek medical advice
See a clinician if you think you have oral thrush, particularly if it is your first episode, if symptoms are not improving with treatment, or if it keeps returning. Get advice promptly if swallowing becomes painful or difficult, as thrush can sometimes extend further down the throat and needs assessment.
Thrush in a newborn baby, or in anyone with a weakened immune system, should be assessed sooner, and any white patch in the mouth that does not settle deserves review to confirm the cause. A pharmacist can offer advice and help you decide whether you need to see a clinician.
Frequently asked questions
Is oral thrush a sign of poor hygiene?
No. Oral thrush is caused by an overgrowth of Candida yeast when the natural balance in the mouth is upset, often by antibiotics, inhalers, dentures or a health condition, rather than by poor hygiene.
How is oral thrush treated?
It is usually treated with an antifungal held in the mouth, such as an oral gel or suspension, over a course of several days. More extensive cases may be treated with an antifungal tablet after assessment.
Can a steroid inhaler cause oral thrush?
Yes. Steroid inhalers can make thrush more likely. Rinsing your mouth and, where used, cleaning a spacer after each dose helps reduce the risk.
How long does oral thrush take to clear?
With treatment it usually starts to improve within a few days and settles over about a week to ten days. Completing the full course helps prevent an early return.
Why does my oral thrush keep coming back?
Recurrent thrush is often linked to an underlying factor such as inhaler technique, denture fit, a dry mouth or diabetes. A clinician can help identify and manage the cause.
When should I see someone about oral thrush?
Seek advice for a first episode, if symptoms do not improve with treatment, if swallowing becomes painful, or for thrush in a baby or anyone with a weakened immune system.