What is oral thrush and why do I keep getting it?

Q. I've had thrush three times this year. What is thrush? Why might this be happening?

A. Thrush is an infection of the mouth caused by a common yeast called Candida (pronounced CAN-did-a). It often causes a whitish coating on the tongue, inside the cheeks, and in the back of the throat. Some people find that food tastes differently than usual.

We all have Candida on our skin and in our mouths. But it's usually kept in check by your immune system. Also, "normal" bacteria that live on the skin and in the mouth compete with the Candida for nutrients. So, Candida does not overgrow.

Thrush can be a problem that happens over and over for people with dentures. The wet, warm space underneath the denture is an ideal place for candida to multiply.

Thrush often happens if you need to stay on an antibiotic for an extended period of time, or if you have taken several different antibiotics within a year. Antibiotics kill bacteria that normally keep Candida numbers in control.

A weakened immune system from chemotherapy or radiation therapy for cancer, or from a disease like AIDS, can also give Candida an opportunity to grow.

Doctors commonly treat thrush with the medicine clotrimazole, taken as a troche. A troche is medicine in lozenge form that dissolves in the mouth. If that doesn't work, a stronger anti-Candida pill, fluconazole (Diflucan), usually will.

If you wear dentures, it's important to remove and clean them at bedtime and to soak them overnight in Efferdent, Polident, or some similar product.

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