Oral Thrush: Causes, Symptoms and Treatments

July 12, 2016 at 4:10 PM

Written by Christian Nordqvist

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 Candida albicans, but may also be caused by Candida glabrata or Candida tropicalis.

Candidosis or Moniliasis refers to adult oral thrush, while "oral thrush" can refer to both adults and babies.

You can read our article about oral thrush in babies here.

Contents of this article:
 1.  Causes and risk factors of oral thrush
 2.  Symptoms, diagnosis and treatment of oral thrush


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 substantial problems
  • Candida cause oral thrush
  • 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
  • Oral thrush 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
  • Treatment of the condition depends on the initial cause
  • Drug treatments often include nystatin, amphotericin or miconazole
  • Heavy smokers are more likely to have oral thrush.


What is oral thrush?

Oral thrush causes thick white or cream-colored deposits, most commonly on the tongue or inner cheeks.

The lesions can be painful and may bleed slightly when they are scraped. The infected mucosa of the mouth may appear inflamed and red.
Oral thrush can sometimes spread to the roof of the mouth and the back of the throat.oral_thrush.jpg

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

People with poorly controlled diabetes, those taking steroids (especially long-term), as well as individuals who wear dentures have a higher risk of developing oral thrush with more severe symptoms.

Long-term antibiotic therapy can increase the risk of developing oral thrush. Some medications, especially those that dry out the mouth can cause oral thrush to develop. The National Health Service (NHS), UK, mentions that oral thrush is more common among patients who receive chemotherapy or radiotherapy to the head and neck.

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.


Causes of oral thrush

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 35 - 50% of the world's population.

However, people on certain medications, reduced immune systems and certain conditions/illnesses are susceptible to oral thrush when C. albicans can get out of control.


Risk factors for oral thrush

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

  • 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 reproducing 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 saliva (xerostomia) are more prone to oral thrush
  • Diet - malnutrition, whether caused by poor diet or a disease that hinders nutrient absorption, predisposes people to oral thrush. 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.


Symptoms of oral thrush

Oral thrush in adults generally appears as thick, white or creamy-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 creamy or white-colored deposits are scraped, bleeding may occur.

The white spots may join together to form larger ones, also known as plaques; which may then take on a grayish or yellowish color.oral_thrush2.jpg

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 grouped into three groups based on appearance, although the condition can sometimes sit between categories:

  • Pseudomembranous: the classic and most common version of oral thrush; it accounts for around 35% of oral candidiasis cases.
  • 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, 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.


Treatments for oral thrush

Doctors will usually prescribe anti-thrush drugs, such as nystatin, amphotericin or miconazole in the form of drops, gel or lozenges. The patient may alternatively be prescribed a topical oral suspension which is washed around the mouth and then swallowed.

Oral or intravenously administered anti-fungals 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.