A yeast infection in your mouth, called oral thrush, happens when a fungus called Candida that normally lives in your mouth grows out of control. In healthy people, your immune system and the natural balance of bacteria keep this fungus in check. When something disrupts that balance, the fungus multiplies and forms white, raised patches on your tongue, inner cheeks, and other soft tissues.
What Triggers the Overgrowth
Candida lives in the mouths of most people without causing problems. It only becomes an infection when your body’s defenses drop or when something shifts the environment inside your mouth in the fungus’s favor. Several common triggers can set this off.
Medications are one of the most frequent causes. Antibiotics kill bacteria throughout your body, including the helpful bacteria in your mouth that compete with Candida for space and nutrients. With that competition removed, the fungus can multiply rapidly. Inhaled corticosteroids, commonly used for asthma, are another major trigger. A large study of over 52,000 people starting inhaled steroid therapy found they were nearly three times more likely to develop oral thrush in the first three months of use. That risk stayed elevated for at least a year. Oral corticosteroids, such as prednisone, carry a similar risk because they suppress your immune system more broadly.
Weakened immunity is the other big category. Conditions like HIV reduce the immune cells that keep Candida in check. Diabetes is another significant risk factor: high blood sugar impairs the ability of your white blood cells to find and destroy the fungus, and the extra sugar in your saliva may feed Candida growth. Cancer treatments, organ transplant medications, and anything else that suppresses your immune system can open the door to thrush.
Risk Factors for Specific Groups
Denture wearers face an unusually high risk. Research estimates that denture stomatitis, a form of thrush under the denture plate, affects up to 67% of denture wearers worldwide. The warm, moist space between the denture and your gums is an ideal environment for Candida, especially if the denture fits poorly, isn’t cleaned regularly, or is worn overnight. People with full dentures are more likely to develop the condition than those with partials or implant-supported options.
Infants are also highly susceptible because their immune systems are still developing. In breastfeeding families, a cycle of reinfection can develop: the baby passes the fungus to the mother’s nipples during feeding, and the mother’s breasts then become a continuous source of Candida, reinfecting the infant. Breaking this cycle requires treating both mother and baby at the same time.
Older adults, particularly those in nursing care who drink very little fluid, are at increased risk because a dry mouth lacks the saliva that helps wash away excess fungus and maintain a healthy balance of microorganisms.
What Oral Thrush Looks and Feels Like
The hallmark sign is creamy white patches on your tongue, inner cheeks, or the roof of your mouth. These patches are slightly raised and often described as looking like cottage cheese. If you scrape or rub them, they may bleed slightly. Other common symptoms include:
- Redness and burning inside your mouth, sometimes severe enough to make eating or swallowing difficult
- Cracking at the corners of your mouth
- A cottony feeling in your mouth, as if you have a film coating your tongue
The patches can also appear on your gums, tonsils, and the back of your throat. In mild cases, you might notice only a small patch on your tongue with slight discomfort. In more severe cases, especially in people with weakened immune systems, the infection can spread down into the esophagus, making swallowing painful.
How It’s Diagnosed
Doctors and dentists can usually diagnose oral thrush just by looking at the characteristic white patches. If confirmation is needed, they may take a small swab of the affected area and examine it under a microscope. A solution is applied that dissolves mouth cells but leaves the Candida intact, making the fungus easy to identify. In less common cases where the patches are thick and hardened, a small tissue sample may be taken for closer analysis.
How Oral Thrush Is Treated
For mild cases, treatment typically involves an antifungal medication applied directly inside the mouth. This might be a medicated lozenge you dissolve on your tongue or a liquid suspension you swish around your mouth before swallowing. These topical treatments are used for 7 to 14 days and clear most mild infections.
Moderate to severe cases usually require an oral antifungal pill taken once daily for 7 to 14 days. If thrush keeps coming back, your doctor may recommend taking an antifungal pill three times a week as a preventive measure. For stubborn infections that don’t respond to the first-line treatment, stronger antifungal options are available, sometimes used for up to four weeks.
For denture-related thrush, treatment works best when combined with thorough denture cleaning. Soaking your dentures overnight in an antifungal solution and leaving them out as much as possible while healing helps prevent the fungus from recolonizing the denture surface.
Reducing Your Risk
Good oral hygiene is the most effective prevention strategy. Brush with a soft toothbrush, clean between your teeth daily, and consider using an antiseptic mouthwash. If you wear dentures, clean them thoroughly every day with a brush and a dedicated cleaning solution, and avoid sleeping with them in.
If you use an inhaled corticosteroid for asthma or another lung condition, rinsing your mouth with water after each use is one of the simplest ways to reduce your risk. This washes away the medication residue that would otherwise settle on your oral tissues and suppress the local immune response.
Staying well hydrated keeps your mouth moist and your saliva flowing, which naturally limits fungal growth. Some people also use probiotics to help maintain a healthy balance of microorganisms in the mouth, though evidence for this approach is still limited. If you have diabetes, keeping your blood sugar well controlled reduces the immune impairment and excess oral sugar that allow Candida to thrive.