ANDY'S ANSWER: Thrush is an oral fungal infection that happens when Candida (a naturally-occurring yeast in the body) grows out of control. Anyone can get thrush at any age, especially if they have a weakened immune system, but it's most common in babies or older people. It's normally not considered serious, but it can be very uncomfortable.
Thrush looks like cottage cheese on the tongue or inside the cheeks. The white patches are hard to remove and may bleed if you try and rub them off. You will also have a sore mouth and may have difficulty eating or drinking.
Thrush may clear up on its own, or with help of a warm saltwater rinse several times a day if its just a minor infection. If the infection persists or continually recurs, you should see your doctor.