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

Candida is a yeast-like fungus that is part of the normal flora of the gut and mouth, and NICE Clinical Knowledge Summaries says that colonisation is usually symptomless. Trouble starts when the mouth's defences are lowered or its lining is disturbed, allowing the yeast to multiply and cause infection.

The NHS describes oral thrush as usually harmless and says it is common in babies and in older people with dentures. NICE CKS notes that several types exist, including pseudomembranous candidiasis (the classic white patches), denture stomatitis and chronic plaque-like candidiasis, and that most cases are caused by Candida albicans.

In adults the NHS says the inside of the mouth is red with white patches, and that wiping the patches away leaves red spots that can bleed. A baby typically has a white coating on the tongue that looks like cottage cheese and does not rub off easily, sometimes with white spots in the mouth, and may not want to feed.

• Cracks at the corners of the mouth.

• Not tasting things properly, or an unpleasant taste.

• Pain inside the mouth, such as a sore tongue or sore gums.

• Difficulty eating and drinking.

• In babies: reluctance to feed and a white coating on the tongue.

The NHS lists taking antibiotics over a long time, using asthma inhalers and having cancer treatment such as chemotherapy as situations where the fungus can grow more than usual. NICE CKS adds comorbidities that increase the risk of candidal infection, including diabetes mellitus, severe anaemia and immunocompromise from chemotherapy, radiotherapy, HIV infection and AIDS.

Other risk factors in NICE CKS are poor dental hygiene, local trauma, smoking, broad-spectrum antibiotics, inhaled or oral corticosteroids and malnutrition. The NHS dry mouth page also lists oral thrush among the causes of a dry mouth, so the two conditions can occur together.

Dentures deserve particular mention. The NHS advises people not to wear dentures at night, not to keep wearing ones that do not fit properly, and to clean them. Denture stomatitis, the type of oral candidiasis that sits under a denture, is named in NICE CKS, so denture care is part of treatment as well as prevention.

Most cases are diagnosed from the appearance of the mouth. The NHS points readers who are not sure it is thrush to look at other causes of a white or sore tongue. NICE CKS advises arranging referral or specialist advice if there is doubt about the diagnosis, and swabbing to identify the organism is one step it lists when infection has not cleared on treatment.

A particular warning in NICE CKS concerns chronic plaque-like candidiasis that does not respond to treatment: referral for biopsy should be considered because it carries a risk of malignancy. White patches that do not wipe off and do not clear after treatment therefore deserve a clinician's examination rather than repeated self-treatment.

The NHS says a mouth gel bought from a pharmacy can treat oral thrush in adults, children and babies over 4 months, and to follow the instructions on the packet. For someone whose immune system is working normally, NICE CKS recommends a topical antifungal first: miconazole oral gel is first-line for children aged 4 months and over, with nystatin suspension offered if miconazole is unsuitable.

If topical treatment fails, the infection is extensive or severe, or the person is significantly immunocompromised, NICE CKS advises oral fluconazole for people aged 16 and over for at least 14 days, followed by a review and possibly a further 7 days. It also lists swabbing, specialist advice or referral to a dermatologist, and monitoring for liver effects if treatment lasts more than 21 days. For under-16s, or when fluconazole cannot be used, specialist advice is sought. These are prescriber decisions, and nothing here is a dosing instruction.

The NHS prevention advice is to brush teeth twice a day, clean dentures, keep up regular dental check-ups even if you have dentures, brush gums and tongue with a soft brush if you have no teeth, and rinse your mouth after eating or taking medicine. If you use an inhaler that contains a steroid, rinsing the mouth afterwards is a sensible habit, and a pharmacist can advise on technique. People with a long-term condition such as diabetes are advised to attend regular check-ups, since poor control encourages yeast overgrowth.

For babies, the NHS recommends sterilising dummies and bottles. The NHS also says not to smoke. Anyone who has repeated episodes should mention that to their GP or dentist, because NICE CKS lists recurrent oral candidiasis as a reason for referral or specialist advice.

The NHS says to see a GP if your baby is under 4 months and has signs of oral thrush, if there is no improvement after 1 week of treatment with a mouth gel, or if you have difficulty or pain when swallowing. NICE CKS treats difficulty or pain on swallowing or pain behind the breastbone as a possible sign of oesophageal candidiasis, one reason for admission if infection is widespread or the person is unwell.

Dentists can examine the mouth and denture fit, and private dental or medical appointments are an option for people who would rather not wait, but the same stepwise approach applies. Treatment should be matched to the cause rather than repeated indefinitely.