Thrush is a fungal infection caused by an overgrowth of Candida, a type of yeast that naturally lives on your skin and inside your body. It most commonly appears in the mouth or the vaginal area, though it can develop anywhere warm and moist. The yeast responsible, primarily Candida albicans, is found in the oral cavity of up to 75% of the population without causing any problems. It only becomes an infection when something disrupts the balance that normally keeps it in check.
Why Candida Overgrows
Candida albicans is a lifelong, harmless part of your normal microbiome. It coexists with bacteria and other microorganisms that compete for space and resources, keeping yeast numbers low. When that microbial balance shifts, Candida can multiply rapidly and change form, switching from a round yeast cell into long, thread-like filaments that penetrate tissue and cause inflammation.
Several things can tip the balance. Antibiotics are one of the most common triggers because they kill off protective bacteria along with harmful ones, leaving Candida with less competition. Corticosteroids, especially inhaled steroids used for asthma, suppress the local immune response in the mouth and throat. Conditions that weaken the immune system more broadly, like diabetes, HIV/AIDS, and cancer, also increase risk significantly. Even everyday factors play a role: wearing dentures, smoking, and medications that cause dry mouth all create an environment where Candida thrives.
Oral Thrush: What It Looks and Feels Like
Oral thrush produces creamy white patches on the tongue, inner cheeks, and sometimes the roof of the mouth, gums, or tonsils. These slightly raised patches have a distinctive cottage cheese-like texture. If you scrape or rub them, they may bleed slightly, revealing red, irritated tissue underneath.
Beyond the visible patches, oral thrush often causes a burning or sore sensation that can make eating and swallowing difficult. You might notice a cottony feeling in your mouth, loss of taste, or cracking and redness at the corners of your lips. People who wear dentures commonly experience redness, irritation, and pain beneath the denture plate.
Vaginal Thrush: Symptoms and Frequency
Vaginal thrush (also called a vaginal yeast infection) is extremely common. Roughly 75% of women will experience at least one episode in their lifetime. The hallmark symptom is a thick, white, adherent discharge, often described as clumpy or paste-like. It’s accompanied by intense itching, burning, and irritation of the vulva and vaginal area. Visible signs include redness, swelling, and sometimes small skin breaks from scratching.
One distinguishing feature is vaginal pH. During a yeast infection, pH typically stays below 5, which is more acidic than what you’d see with bacterial infections. This is one reason doctors sometimes test pH to help narrow down the cause of symptoms.
For some women, thrush keeps coming back. Recurrent vulvovaginal candidiasis is defined as three or more symptomatic episodes within a single year, with periods of improvement in between. This pattern often requires a different management approach than a one-time infection.
How Thrush Is Diagnosed
A doctor can often diagnose oral thrush just by looking at the characteristic white patches. Vaginal thrush is similarly recognizable from symptoms and a physical exam, but when the diagnosis isn’t clear-cut, a simple lab test can confirm it. A small sample of the affected tissue or discharge is placed on a glass slide with a potassium hydroxide solution, which dissolves skin cells and makes fungal structures visible under a microscope. Seeing branching filaments or budding yeast cells confirms the infection.
If that test comes back negative but thrush is still suspected, a fungal culture can provide a definitive answer, though cultures are more expensive and can take weeks to return results. In practice, most straightforward cases of thrush are diagnosed and treated based on symptoms alone.
Treatment for Oral Thrush
Oral thrush is treated with antifungal medications applied directly inside the mouth. The most common is a liquid suspension that you swish around your mouth before swallowing, typically taken four times a day. Lozenges and tablets that dissolve slowly in the mouth are also available for adults and children over five. Treatment generally lasts up to 14 days, and it’s important to finish the full course even if symptoms clear up earlier, since stopping too soon can allow the infection to return.
For more stubborn or widespread infections, particularly in people with weakened immune systems, doctors may prescribe a systemic antifungal taken by mouth as a pill. These work throughout the body rather than just locally.
Treatment for Vaginal Thrush
Most vaginal yeast infections can be treated with over-the-counter antifungal creams or suppositories. These come in different regimen lengths, typically one-day, three-day, or seven-day courses. The shorter courses use higher concentrations of medication, while the seven-day option uses a lower concentration spread over more time. Both approaches are effective, and the choice often comes down to personal preference and severity.
A single-dose oral antifungal pill is another option, available by prescription in many countries. For recurrent infections, longer or repeated treatment courses may be necessary to break the cycle of relapse.
Can Probiotics Help Prevent Recurrence?
There’s growing interest in using probiotics, particularly Lactobacillus strains, to prevent thrush from coming back. The evidence is promising but inconsistent. When probiotics are used alongside standard antifungal treatment, studies show improved short-term cure rates and reduced relapse rates. One systematic review found a significant reduction in recurrence at one month post-treatment in people who took probiotics compared to those who didn’t. Another trial found that 73% of women in the probiotic group remained recurrence-free at three months, compared to just 35% in the placebo group.
The challenge is that studies use different probiotic strains, doses, and schedules, making it hard to recommend one specific product. What the research does consistently show is that probiotics are safe and well-tolerated. For women dealing with recurrent vaginal thrush, adding a probiotic alongside antifungal treatment is a low-risk strategy that may meaningfully reduce the chance of another episode.
When Thrush Becomes Serious
For most people, thrush is a surface-level nuisance that clears up with treatment. In rare cases, however, Candida can enter the bloodstream and cause invasive candidiasis, a serious systemic infection. This almost exclusively happens in people who are already critically ill or have specific medical vulnerabilities: prolonged intensive care stays, central venous catheters, very premature infants with low birth weight, people undergoing chemotherapy or organ transplants, or those on long courses of broad-spectrum antibiotics.
A routine case of oral or vaginal thrush in an otherwise healthy person does not progress to invasive disease. But in people with severely compromised immune systems, even a mouth infection warrants close attention and prompt treatment to prevent the yeast from spreading deeper.