Mouth thrush, also called oral candidiasis, is a fungal infection that produces creamy white, slightly raised patches inside your mouth. It’s caused by an overgrowth of a yeast called Candida albicans, a fungus that already lives in the mouths of 30 to 60% of healthy adults without causing any problems. When something disrupts the balance of your immune system or the normal bacteria in your mouth, this yeast multiplies beyond what your body can keep in check.
Why Candida Overgrows
Under normal conditions, your immune system and the bacteria that naturally live in your mouth keep Candida populations small and harmless. Thrush develops when that balance tips. The disruption can be local, like residue from a corticosteroid inhaler sitting on the tissues of your mouth, or systemic, like a weakened immune system from an underlying illness.
The CDC notes that thrush is uncommon in healthy adults. The risk is highest in babies under one month old. Beyond infancy, the conditions most strongly linked to oral thrush are diabetes, HIV/AIDS, and cancer. Other well-established risk factors include:
- Antibiotics: They kill off the bacteria that normally compete with Candida for space in your mouth.
- Corticosteroid inhalers: Used for asthma and COPD, these deposit medication directly onto oral tissues.
- Dentures: Especially poorly fitting ones, which create warm, moist pockets where yeast thrives.
- Dry mouth: Saliva helps control fungal growth, so anything that reduces it (certain medications, radiation therapy) raises the risk.
- Smoking: Alters the oral environment in ways that favor Candida colonization.
- Malnutrition and vitamin deficiencies: A poorly nourished immune system is less effective at keeping yeast in check.
What It Looks and Feels Like
The hallmark sign is white patches or spots that look like cottage cheese on your tongue, inner cheeks, and sometimes the roof of your mouth, gums, or tonsils. These patches are slightly raised and can be sore. If you scrape or rub them, they may bleed slightly. Many people also develop cracking and redness at the corners of the mouth, a related condition called angular cheilitis.
Thrush can make eating uncomfortable, and some people describe a cottony feeling in the mouth or a loss of taste. In more severe cases, the soreness can make swallowing painful, which sometimes signals that the infection has started to spread deeper into the throat or esophagus.
Thrush in Babies and Breastfeeding
Infants are especially prone to thrush because their immune systems are still developing. In a breastfeeding pair, the infection can pass back and forth: the baby develops white patches in the mouth, and the mother’s nipples become a reservoir for the fungus, leading to persistent reinfection. Treating only the baby often fails because the yeast recolonizes from the mother’s skin at the next feeding. Both the infant and the breastfeeding parent need to be treated simultaneously to break the cycle.
How It’s Treated
Mild thrush is typically treated with a topical antifungal, a medicated liquid or gel that you swish around your mouth and then swallow or spit out. Treatment usually lasts 7 to 14 days, applied several times a day. For moderate to severe cases, or when topical treatment isn’t enough, doctors prescribe an oral antifungal tablet. The oral form is absorbed very efficiently, with over 90% of the drug reaching your bloodstream, so it works well even without an IV.
Most people start feeling better within a few days of starting treatment, though finishing the full course matters to prevent the infection from bouncing back. People with weakened immune systems may need longer treatment or a higher dose, and recurrent thrush sometimes requires ongoing preventive therapy.
Preventing Inhaler-Related Thrush
If you use a corticosteroid inhaler, thrush prevention comes down to keeping medication residue out of your mouth. The most effective steps are rinsing your mouth with water (or a baking soda solution), gargling, and then spitting after every inhaler use. Brushing your teeth right after using the inhaler also works. Simply drinking a glass of water is not enough, because the medication residue that settles on the back of the throat and tongue isn’t adequately cleared by swallowing alone.
Using a spacer device, the tube that attaches between the inhaler and your mouth, makes a significant difference. Spacers reduce the amount of medication that lands on your oral tissues by improving how much of the drug actually reaches your lungs, where it belongs. Medium to large volume spacers with one-way valves are the most effective. Metal or antistatic-lined models outperform basic plastic ones because they avoid static charge that traps the drug inside the device.
If you smoke and use an inhaler, quitting reduces thrush risk directly and may also allow your doctor to lower your inhaler dose over time, further reducing exposure.
The Sugar Connection
There’s a reason thrush is more common in people with poorly controlled diabetes. Lab research shows that Candida albicans grows faster in the presence of glucose: higher glucose concentrations directly shorten the time the yeast needs to reproduce. In the same study, fructose actually slowed Candida’s growth rate, nearly doubling the time needed for the fungus to replicate compared to glucose. This suggests that the high blood sugar levels in uncontrolled diabetes create a more hospitable environment for yeast in the mouth.
Whether cutting dietary sugar helps someone who already has thrush and normal blood sugar is less clear. But for people with diabetes, keeping blood sugar well controlled is one of the most effective ways to reduce the frequency of oral thrush episodes.
What Happens if Thrush Goes Untreated
In people with healthy immune systems, mild thrush sometimes resolves on its own, but it can also linger and worsen. The bigger concern is for anyone with a compromised immune system. Untreated oral thrush can spread from the mouth down into the esophagus, causing pain and difficulty swallowing. In severely immunocompromised individuals, there is a risk of the infection entering the bloodstream, which becomes a serious medical situation requiring hospital-level care. Candida albicans accounts for the vast majority of oral thrush cases (over 80%), but other Candida species can also be involved, and some of these are harder to treat with standard antifungals.
Denture Care and Oral Hygiene
If you wear dentures, daily cleaning and disinfection are essential for preventing thrush. Soaking dentures in an antimicrobial solution and then air-drying them removes the biofilm where Candida likes to hide. Dentures should be taken out for at least six hours each night to give your oral tissues a chance to recover. Brushing your teeth at least twice a day with a fluoride toothpaste (at a concentration of at least 1,000 ppm fluoride) helps maintain the bacterial balance in your mouth that keeps Candida from overgrowing.