Oral thrush in adults (oral candidiasis): causes, symptoms and treatment

Candida is part of the normal oral flora of many people, so merely finding yeasts on a culture or swab does not mean disease. In a case-control study from Sri Lanka (250 people with type 2 diabetes and 81 without diabetes), oral Candida carriage was similar in both groups (81%), whereas a high yeast count (above 2,000 CFU/ml) was found in 32.8% of people with diabetes against 12.3% of healthy people. The difference was linked to wearing dentures, female sex and smoking.

This difference between presence and mass overgrowth explains why thrush is not a simple consequence of 'catching a fungus'. Infection develops when conditions in the mouth change: saliva production falls, the bacterial flora is disturbed, saliva glucose rises, a damp environment forms under a denture, or immunity weakens locally or generally. That is why treating symptoms alone without considering the cause often ends in recurrence.

The 2016 IDSA guideline lists HIV infection, diabetes, leukaemia and other cancers, steroid use, radiotherapy, antibiotic therapy and denture use as conditions in which oropharyngeal and oesophageal candidiasis occur; the authors stress that its occurrence is recognised as an indicator of immune dysfunction. In people infected with HIV, thrush is most often seen at CD4 counts below 200 cells/µl, and effective antiretroviral therapy has dramatically reduced its frequency.

This is important for people with asthma and COPD, because inhaled steroids are drugs that must not be stopped on your own, and yet thrush is one of their most common local side effects. A 2025 narrative review notes that the main risk factors include high ICS doses, poor oral hygiene and incorrect inhaler technique, and that preventive methods include spacers, rinsing the mouth after inhalation and proper denture care. We write about asthma treatment in our entry on asthma.

A denture is a separate, very important factor. In a cross-sectional study of older people (91 people), yeasts were grown from 83.3% of denture wearers and 53.5% of people without dentures (OR 4.3), and symptomatic candidiasis occurred mainly in denture wearers. The authors link the risk to dentures and insufficient oral hygiene. At the same time, older people with diabetes had a 4.4-fold higher estimated risk of candidiasis, although no statistically significant association was shown linking dentures and diabetes to the onset of the disease, which shows how hard it is to separate these factors in small samples.

The typical form is creamy-white plaques on the tongue, the lining of the cheeks, the palate or the throat, which can often be wiped off with gauze, revealing a reddened, sometimes slightly bleeding surface. Symptoms are burning, a feeling of dryness, altered taste and soreness when eating. Candidiasis may also involve the corners of the mouth (angular cheilitis: cracks and redness). People with dentures can have inflammation of the mucosa under the denture with redness over the palate, often without clear white plaques.

Not every white coating is thrush. A white film on the tongue can also be an ordinary coating in smokers or people who neglect hygiene, and a white patch that cannot be wiped off needs assessment by a dentist or doctor, because it may be leukoplakia, lichen planus or another change, including rarely a precancerous one. The diagnosis of thrush is most often clinical, and a swab with culture is considered for recurrences or lack of response to treatment, which also matters because fluconazole resistance is linked mainly to repeated, long-term exposure to azoles.

Symptoms such as pain on swallowing, a feeling of food sticking behind the breastbone or difficulty swallowing suggest the fungus may have involved the oesophagus (oesophageal candidiasis). That is a different clinical situation from oral thrush, always requiring systemic treatment and a doctor's assessment, as we describe in the section on warning signs.

Several practical conclusions follow from the guideline. First, topical treatment is the first-choice method in mild cases. Second, it is not short: 7-14 days, even if symptoms ease sooner. Third, the form of the drug matters: troches and suspensions act locally, which is why they are used several times a day. Fourth, in a study of people infected with HIV, a once-daily mucoadhesive miconazole tablet was as effective as clotrimazole troches five times a day, which can make it easier to stick to treatment.

We do not treat the doses and forms of drugs here as recommendations for self-treatment: the choice of preparation, duration of treatment and contraindications are decided by a doctor or pharmacist on the basis of the leaflet. The availability of specific preparations differs between countries, so we do not discuss brand names or reimbursement.

Data from the HIV population should be interpreted with caution, because these people have deeper immune disorders than most adults with thrush after an antibiotic or an inhaled steroid. In this group fluconazole did better than nystatin, which agrees with the IDSA review, which describes that in people with HIV symptomatic relapses came sooner and more often with topical treatment than with fluconazole. In people with normal immunity and mild changes topical treatment usually suffices, and fluconazole is reserved for more severe forms, recurrences or cases where topical treatment has failed.

Fluconazole is an effective drug, but not without reservations. The 2023 safety review of antifungal drugs stresses that fluconazole has numerous cytochrome P450 interactions, so before it is used the doctor should know all the medicines the patient takes. With repeated courses the risk of resistance also rises: IDSA describes that resistance to fluconazole and other azoles is mainly the result of earlier, repeated and long-term exposure to these drugs.

On the other hand, the studies we cite do not show that herbal rinses, baking soda, yoghurt or supplements effectively treat or prevent thrush. We did not find randomised trials in this article that confirm it, so we do not recommend replacing antifungal treatment with them. At most they may ease discomfort, and some (for example hot, irritating rinses) may make it worse.

What can the work-up of recurrent thrush include? The doctor usually starts with the history: which inhaled drugs, antibiotics, steroids and immunosuppressants you take, whether you wear a denture, what your oral hygiene is like, whether your mouth is dry. Then they consider tests for diabetes (fasting glucose, glycated haemoglobin, which we write about in our entry on HbA1c), sometimes a blood count and other tests depending on the clinical picture, and in people with risk factors also an HIV test. In some situations a swab with culture is taken to confirm the diagnosis and the species of fungus.

As for treating recurrences, IDSA notes that chronic suppressive therapy is usually unnecessary, and for recurrences fluconazole 100 mg three times a week can be considered; the doctor decides this after assessing the risks and drug interactions. In people with HIV, antiretroviral therapy is recommended as a way to reduce the number of recurrences. These recommendations do not apply to typical thrush after a single course of antibiotics, which most often clears after treatment and removal of the cause.

Thrush in adults is usually a sign that something has changed the conditions in the mouth: a drug, a denture, sugar or immunity. Good management therefore has two parts. The first is treating the infection itself with an antifungal for as many days as the leaflet or doctor advises. The second is finding and removing the cause: improving inhalation technique, denture hygiene, diabetes control, a review of medicines. If the second step is skipped, thrush returns, and repeated courses of fluconazole raise the risk of resistance.