Thrush is caused by forms of a fungus called Candida. This organism lives in your mouth and is usually kept in check by healthy organisms that also live there. However, when your resistance to infection is low, the fungus can grow, leading to lesions in your mouth and on your tongue.

The following can lessen your resistance to infection and increase your chances of getting thrush:

• Taking antibiotics or steroid medications
• Having HIV infection or AIDS
• Receiving chemotherapy for cancer or drugs to suppress your immune system following an organ transplant
• Being very old or very young
• Being in poor health
• Having diabetes

Thrush is commonly seen in infants. It is not considered abnormal in infants unless it lasts longer than a couple of weeks.

Candida can also cause yeast infections in the vagina.

Thrush appears as whitish, velvety lesions in the mouth and on the tongue. Underneath the whitish material, there is red tissue that may bleed. The lesions can slowly increase in number and size.

If you are immunocompromised (for example, you are HIV positive or receiving chemotherapy), the infection can spread to other organs, such as the esophagus (causing pain with swallowing), or throughout your body, which can be deadly.

Your doctor or dentist can almost always diagnose thrush by looking at your mouth and tongue. These fungal lesions have a distinct appearance. If not entirely clear, one of the following tests may be performed to look for the candida organisms:

• Microscopic examination of mouth scrapings
• Culture of mouth lesions