Oral thrush, also known as oral candidiasis, is a yeast/fungi infection of the genus Candida that develops on the mucous membranes of the mouth.

It is most commonly caused by the fungus Candida albicans, but may also be caused by Candida glabrata or Candida tropicalis.

For the majority of individuals, oral thrush does not cause any serious problems. However, this is not the case for people with a weakened immune system, whose signs and symptoms may be much more severe.

The outcome for oral thrush is generally very good. Most people respond well to treatment. However, oral thrush tends to reappear, especially if the causal factor (smoking, for instance) is not removed.

In this article, we will cover all aspects of oral thrush, including the causes, symptoms, and treatment.

Fast facts on oral thrush

Here are some key points about oral thrush. More detail and supporting information is in the main article.

  • Oral thrush is a common condition, but for most, it does not cause major problems.
  • Individuals with a reduced immune system are worst affected by oral thrush.
  • Oral thrush can occur more regularly after chemotherapy or radiotherapy to the head and neck.
  • It is more common in people who are taking steroids, wear dentures, or have diabetes.
  • The most obvious symptom of oral thrush is creamy or white-colored deposits in the mouth.

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Oral thrush is caused by species of Candida fungus.

Doctors will usually prescribe anti-thrush drugs, such as nystatin or miconazole in the form of drops, gel, or lozenges.

Alternatively, the patient may be prescribed a topical oral suspension which is washed around the mouth and then swallowed.

Oral or intravenously administered antifungals may be the choice for patients with weakened immune systems.

If treatment is not working, amphotericin B may be used; however, this will only be used as a last resort due to the negative side effects which include fever, nausea, and vomiting.

Alongside medical treatment, the following can help reduce the risk of worsening the condition:

  • Rinse mouth with salt water.
  • Use a soft toothbrush to avoid scraping the lesions.
  • Use a new toothbrush every day until the infection has gone.
  • Eat unsweetened yogurt to restore healthy bacteria levels.
  • Do not use mouthwashes or sprays.

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Oral thrush is typically diagnosed after an oral examination.

Oral thrush in adults generally appears as thick, white or cream-colored deposits (spots) on the mucous membrane of the mouth (wet parts of the inside of the mouth).

The mucosa (mucous membrane) may appear swollen and slightly red. The spots may be raised. There may be discomfort or a burning sensation.

If the cream or white-colored deposits are scraped, bleeding may occur.

The white spots may join together to form larger ones, also known as plaques; these may then take on a grayish or yellowish color.

Occasionally, the affected area simply becomes red and sore, with no detectable white spots.

Individuals who wear dentures may have areas that are constantly red and swollen under a denture. Poor oral hygiene, or not taking the dentures out before going to sleep may increase the risk.

Oral thrush is sometimes divided into three groups based on appearance, although the condition can sometimes sit between categories:

Pseudomembranous - the classic and most common version of oral thrush.

Erythematous (atrophic) - the condition appears red raw rather than white.

Hyperplastic - also referred to as "plaque-like candidiasis" or "nodular candidiasis" due to the presence of a hard to remove solid white plaque. This is the least common variant; it is most often seen in patients with HIV.

There are a number of other lesions that can also appear with oral thrush. Sometimes, these lesions might be due to other types of bacteria that are also present in the area. These can include:

  • Angular cheilitis - inflammation and/or splitting in the corners of the mouth
  • Median rhomboid glossitis - a large, red, painless mark in the center of the tongue
  • Linear gingival erythema - a band of inflammation running across the gums

Tiny quantities of Candida fungus exist in various parts of our body, including the digestive system, skin, and mouth, causing virtually no problems to healthy individuals. In fact, C. albicans is carried in the mouths of up to 75 percent of the world's population.

However, people on certain medications, with reduced immune systems, or certain medical conditions are susceptible to oral thrush when C. albicans grows out control.

Adult oral thrush is more likely to become a problem for the following groups:

  • People who wear dentures - especially if they are not kept clean, do not fit properly, or are not taken out before going to sleep.
  • Antibiotics - people who are on antibiotics have a higher risk of developing oral thrush. Antibiotics may destroy the bacteria that prevent the Candida from growing out of control.
  • Excessive mouthwash use - individuals who overuse antibacterial mouthwashes may also destroy bacteria which keep Candida at bay, thus increasing the risk of developing oral thrush.
  • Steroid medication - long-term use of steroid medication can increase the risk of oral thrush.
  • Weakened immune system - people with weakened immune systems are more likely to develop oral thrush.
  • Diabetes - people with diabetes, especially if it is poorly controlled, are more likely to have oral thrush.
  • Dry mouth - people with less than normal quantities of saliva (xerostomia) are more prone to oral thrush.
  • Diet - malnutrition predisposes people to oral thrush; this could be caused by a poor diet or a disease that affects the absorption of nutrients. In particular, diets low in iron, vitamin B12, and folic acid appear to affect infection rates.
  • Smoking - heavy smokers are more at risk, the reasons behind this are unclear.

In the vast majority of cases, the doctor can diagnose oral thrush by looking into the patient's mouth and asking some questions about symptoms.

The doctor may scrape some tissue from the inside of the mouth for analysis.

If the doctor believes the oral thrush is being caused by a medication or some other underlying cause, that cause must be dealt with. Treatments in such cases depend on the underlying cause.