Thrush in the mouth, called oral thrush, is a fungal infection caused by an overgrowth of Candida, a type of yeast that normally lives in your mouth in small amounts. When something disrupts the balance of microorganisms in your mouth or weakens your immune system, Candida can multiply and form visible white patches on the tongue, inner cheeks, and other soft tissues. It can affect anyone but is most common in babies, older adults, and people with compromised immune systems.
What Oral Thrush Looks Like
The hallmark sign is creamy white, slightly raised lesions that appear on your tongue, inner cheeks, gums, the roof of your mouth, or the back of your throat. These patches have a cottage cheese-like texture. If you scrape or rub them, the tissue underneath is often red and may bleed slightly.
Beyond the visible patches, thrush can cause a cottony feeling in your mouth, soreness or burning (especially when eating), redness and cracking at the corners of your lips, and a diminished sense of taste. Some people describe a persistent unpleasant taste. Swallowing can become painful if the infection extends toward the throat.
Why It Happens
Your mouth naturally contains small amounts of Candida alongside bacteria that keep it in check. Thrush develops when that balance tips in the yeast’s favor. Several things can trigger this:
- Antibiotics: These kill bacteria throughout the body, including the helpful bacteria in your mouth that normally compete with Candida for space and resources. Without that competition, yeast multiplies.
- Inhaled corticosteroids: If you use a steroid inhaler for asthma or another lung condition, traces of the medication land in your mouth and throat, suppressing the local immune response and encouraging yeast growth.
- Weakened immune system: Conditions like HIV/AIDS, cancer, and organ transplantation (or the medications that follow it) reduce your body’s ability to keep Candida in check. Chemotherapy and radiation therapy, particularly to the head and neck, also raise risk.
- Uncontrolled diabetes: When blood sugar is poorly managed, saliva contains higher levels of sugar. Candida feeds on that sugar and grows more readily.
- Dry mouth: Saliva helps control yeast populations. Medications or conditions that reduce saliva flow create a more hospitable environment for Candida.
- Smoking: Tobacco use independently increases the likelihood of oral thrush.
- Age: Adults 65 and older face higher risk, partly because immune function naturally declines with age and partly because dentures, dry mouth, and medication use become more common.
Thrush in Babies and Breastfeeding
Oral thrush is especially common in infants during the first few months of life, when their immune systems are still developing. You’ll typically see the same white patches on the tongue and inside the cheeks. Babies may become fussy during feeding because of mouth soreness.
Thrush passes easily between a nursing baby and the breastfeeding parent. The yeast can transfer from the baby’s mouth to the nipple, or the other direction, creating a cycle of reinfection. Symptoms on the breast include persistent nipple pain, shiny or flaky skin on the areola, and stabbing pain during or after feeding. Because of this back-and-forth cycle, many healthcare providers treat both the parent and the baby at the same time, even if only one is showing symptoms. Treatment typically involves an antifungal applied directly to both the baby’s mouth and the parent’s breast.
How It’s Diagnosed
A doctor or dentist can usually identify oral thrush just by looking at the characteristic white lesions. In cases where the diagnosis isn’t obvious, they’ll take a sample by lightly scraping the affected area or using a swab. That sample is placed on a slide with a potassium hydroxide solution, which dissolves skin cells but leaves fungal structures intact, making them visible under a microscope. Color stains are sometimes added so the fungus is easier to spot. The result is straightforward: either fungal elements are present or they’re not.
If your doctor suspects the infection has spread deeper, particularly into your esophagus, an endoscopy (a thin camera guided down your throat) may be needed to check for damage below the mouth.
How Thrush Is Treated
Mild oral thrush in otherwise healthy adults and children typically clears within a couple of weeks with antifungal medication. The most common form is a liquid antifungal that you swish around your mouth and then swallow. For more stubborn cases or people with weakened immune systems, a pill-form antifungal may be prescribed for a longer course.
For infants, the antifungal is usually a gel or liquid applied directly inside the baby’s mouth with a clean finger or swab, typically for 7 to 14 days. Improvement usually begins within a few days, but finishing the full course is important to prevent the infection from coming back.
If thrush keeps returning, your doctor will likely look for an underlying cause, such as poorly controlled blood sugar, an immune condition, or a medication that could be adjusted.
When Thrush Spreads to the Esophagus
In people with significantly weakened immune systems, Candida can travel from the mouth down into the esophagus. This is called esophageal candidiasis, and it’s a more serious condition. Symptoms include pain or difficulty when swallowing, chest pain, heartburn, nausea, and abdominal pain. It typically affects people living with HIV, those undergoing chemotherapy, people who have been hospitalized on extended courses of antibiotics, and individuals who are malnourished.
Esophageal candidiasis requires stronger antifungal treatment, usually in pill or sometimes intravenous form, and is an important signal that the immune system needs closer evaluation.
Reducing Your Risk
If you use an inhaled corticosteroid, the single most effective step is rinsing your mouth with water and spitting after every dose. Following the rinse with tooth brushing reduces the risk of thrush even further. Using a spacer device with your inhaler also helps keep more of the medication in your lungs and less in your mouth.
Other practical steps include keeping blood sugar well controlled if you have diabetes, maintaining good oral hygiene (brushing twice daily, flossing, and cleaning dentures nightly if you wear them), and staying hydrated to support saliva production. If you’re on a long course of antibiotics, let your doctor know if you notice white patches or mouth soreness developing so treatment can start early. For breastfeeding parents, keeping nipples dry between feedings and sterilizing pacifiers and bottle nipples regularly can help interrupt the transmission cycle.