The Facts

Oral thrush is a yeast infection of the mouth caused by uncontrolled growth of an organism called Candida albicans.

Candida albicans is an organism that normally makes a quiet home for itself on your skin and doesn't bother anyone. We all carry this organism on our skin, in our mouth, in our gastrointestinal tract (gut) and, for women, in the vagina.

Occasionally the yeast multiplies uncontrollably, causing pain and inflammation. When this occurs, it is called candidiasis. It is also known as moniliasis or a yeast infection.


You don't "catch" oral thrush; the yeast is already there. A number of factors can increase the chance of the yeast growing out of control. The leading cause of oral thrush is overuse or prolonged use of antibiotics.

Yeast must compete with various other organisms, many of them bacteria. These bacteria, which live on the skin and in the intestine and vagina, among other places, are harmless but good at fighting off yeast. When we take antibiotics to deal with disease-causing bacteria, we kill the harmless bacteria as well. Yeast, which is unaffected by antibiotics, is no longer controlled by the bacteria and starts to grow and multiply.

Steroids and some cancer medications weaken the immune system and can also allow yeast to flourish. Oral thrush most often develops in people with diseases that weaken the immune system, such as cancer and AIDS. It can also develop in people with diabetes or in people who have long-term irritation resulting from dentures. Some medications can also change the environment in the mouth, causing the yeast to grow out of control. A common culprit is inhaled corticosteroids - medications used by people with asthma or chronic lung conditions.

Symptoms and Complications

Oral thrush causes curd-like white patches inside the mouth, on the tongue and palate and around the lips. It may also cause cracked, red, moist areas on skin at the corners of the mouth. Thrush patches may or may not be painful.

Making the Diagnosis

To make a diagnosis, your doctor will ask you about recent use of antibiotics or medications, which can weaken the immune system. The doctor will also take into consideration any history of diabetes, cancer, HIV, or other chronic diseases.

Candidiasis is easy to identify. The yeast can be seen under a microscope after being scraped off the affected area. However, since yeast is normally there anyway, your doctor will want to be sure that it's Candida albicans that's causing the problem and not something else.

Treatment and Prevention

Candidiasis isn't normally a dangerous condition except in the rare cases when it enters the blood and spreads to vital organs of people with weakened immune systems.

For oral thrush, a suspension of antifungal medication can be swished in the mouth and swallowed, or sometimes the doctor will have you dissolve an antifungal lozenge in the mouth. For severe and recurrent cases, antifungal medication taken by mouth may need to be taken for extended periods of time.

If the oral thrush is caused by the use of inhaled corticosteroids, rinsing the mouth after using the inhaler will help prevent the infection.