There are four kinds of oral thrush: pseudomembranous, hyperplastic, erythematous and angular cheilitis.
The calling card of the pseudomembranous type is raised white lesions in the mouth that are described as having a cottage-cheese appearance. (If you were planning on having cottage cheese at lunch, we're sorry.) If you scrape them, they tend to bleed. Sometimes, they join together to make larger spots called plaques that can discolor into a yellowish hue. They like to grow on the insides of your cheeks, your tongue and the roof of your mouth.
The hyperplastic type prefers to stay in your cheeks, but unlike the pseudomembranous kind, the plaques can't be scraped off.
Angular cheilitis also involves white plaques, but its hallmark is cracks around the mouth. In a young person, it often signals HIV infection, as does erythematous oral candidiasis, characterized by red lesions on the palate and under the tongue or spots on the mucous membranes of the cheeks.
An infection of your mucous membranes isn't too bad, but if it spreads to your esophagus from, for example, the insertion of a nasogastric tube, things get more serious. Once the infection has spread way back there, your mouth may feel cottony and your sense of taste deadened. Esophageal infections might make you feel like food is stuck in your throat and inhibit your ability to swallow. For people with compromised immune systems, thrush can run rampant, taking over the lungs, liver and intestines.
Because the appearance of some types of oral thrush is so distinctive, it can often be diagnosed simply on sight, although sometimes a sample from one of the white spots is taken and treated with a potassium hydroxide solution, periodic acid-Schiff or Gram stain to spotlight the yeast cells under a microscope.
Thrush in the esophagus, however, is diagnosed by a throat culture (the same cotton throat swab that gets you a strep diagnosis) or an endoscopic exam. An endoscopic exam is reserved for serious cases because it requires anesthesia, but it enables a doctor to get a close look at your esophagus, stomach and duodenum with a camera.
Once you have a diagnosis or oral thrush, the next question on your mind is probably: Where did I get it from?