Patient information from BMJ

Oral thrush: what is it?

Last published:Sep 14, 2022

Oral thrush is an infection some people get in their mouth and throat. It's caused by a fungus called Candida. Thrush can make your mouth sore, but it can usually be easily treated with medicines. There are also things you can do to reduce your chances of getting it again. 

You can use our information to talk to your doctor about the best treatments for you. 

What is oral thrush?

Oral thrush is an infection that can affect almost any part of your mouth and throat. It’s caused by a type of fungus called Candida. The most common variety is called Candida albicans. The medical name for thrush is candidiasis.

It's normal to have a small amount of Candida in your body, including on your skin and in your mouth. This is usually harmless and doesn't cause any symptoms.

But sometimes Candida grows out of control and you get a candidiasis infection in your mouth. You can get thrush on your tongue, your gums, on the inside of your cheeks, on the roof of your mouth, or in your throat. 

You can also get thrush in many other parts of your body, such as your skin or your groin. Babies can get thrush in their nappy area. And women can get thrush in their vagina.

Who gets oral thrush?

Some people are more likely than others to get oral thrush. This is usually because they have another health problem that makes thrush more likely, or because they are taking medicines that weaken their immune system.

Your immune system helps your body fight off infections. When it's weakened, types of fungus that usually live in your body without causing any problems can grow out of control. 

People who are more likely to get oral thrush include:

• People whose immune systems are weakened by medical treatments, such as anti-cancer (chemotherapy) drugs, steroids (their full name is corticosteroids), or radiotherapy

• People whose immune systems are weakened by other condidions, such as AIDS and leukaemia

• People with diabetes. If you've got diabetes, you have too much sugar in your blood. Thrush grows best in a high-sugar environment, which can happen if sugar levels in your blood and saliva are high. Oral thrush can be caused by both type 1 and type 2 diabetes

• People with asthma who take corticosteroids through an inhaler 

• Those with a severe, long-term dry mouth. Thrush grows more easily in a mouth where there isn't much saliva. You can get a dry mouth when you take certain drug treatments, and after radiotherapy or surgery on your neck or head.

Babies are also more likely to get oral thrush because their immune systems aren’t fully developed.

Oral thrush is also more common in people who:

• Smoke

• Wear badly fitting dentures or have poor oral hygiene

• Have recently taken antibiotics (antibiotics can kill friendly bacteria as well as harmful bacteria, and this can allow thrush to grow)

• Are malnourished.

What are the symptoms of oral thrush?

Oral thrush usually appears as white patches in your mouth.

Your mouth may feel sore and you may get a burning feeling on your tongue. 

If you've got thrush in your throat, you may not be able to speak or eat properly. This can make you feel very unwell. Some people find that things taste different when they have oral thrush or that some foods are painful to swallow. 

There are four main types of oral thrush, and they can look quite different.

• Small white patches on the inside of the cheeks, throat, tongue, or gums. The patches come off if you rub them, and they may bleed. This is the most common type of oral thrush.

• Smooth red patches on the roof of your mouth, the back of your tongue, or the inside of your cheeks.

• A type of thrush called angular cheilitis is swelling of the angles of the mouth. The corners of the mouth can looked cracked, scaly, crusty, or red.

• People who wear dentures can get redness and swelling on the roof of their mouth or around their gums where their dentures come into contact with their mouth.

Your dentist may discover you've got oral thrush when you go for a check-up, and may give you some medicine to treat it. 

If you've got any of the symptoms listed above, or if the inside of your mouth looks different from usual, you should see your doctor. Your doctor will probably: 

• Look inside your mouth for white or red patches

• Ask you about your symptoms.

Sometimes the doctor will take a sample from the affected part of your mouth to test it for Candida.

If the patches in your mouth are still there after you've had medicines to get rid of oral thrush, your doctor may refer you to a specialist.

What to expect in the future

If you don't have treatment for oral thrush it can go on for months, or it could keep coming back after it clears up. 

It's especially important to have any white or red patches in your mouth checked out and treated. These patches could be a sign of another condition or, rarely, of the beginnings of cancer.

In young babies, oral thrush usually clears up on its own within a few weeks.