Healthy adults rarely get oral thrush out of the blue. When creamy white patches or a sore, red mouth turn up, there is usually a reason behind it: a recent course of antibiotics, a preventer puffer, dentures worn overnight, diabetes, a dry mouth or a weakened immune system. Treating the yeast clears the patches, but finding that reason is what stops them coming back.
A yeast that normally lives quietly in the mouth
Oral thrush is an overgrowth of Candida, a yeast that many people carry in small numbers without any problem. Saliva, the normal mouth bacteria and the immune system keep it in check. Thrush appears when one of those controls is weakened and the yeast multiplies on the lining of the mouth.
The NHS describes the typical adult picture as a red mouth with white patches, where wiping the patches can leave red spots that may bleed. Other signs include cracks at the corners of the mouth, an altered or unpleasant taste, and pain or soreness inside the mouth. Some adults never get white patches at all and simply have smooth, red, tender areas, often on the tongue or palate, which is one reason an examination helps.
The usual triggers in adults
Antibiotics
Antibiotics reduce the normal bacteria that compete with Candida, giving the yeast room to grow. A sore, red mouth soon after a course of antibiotics is a common pattern.
Preventer puffers
Inhaled corticosteroids used for asthma and COPD leave some medicine in the mouth and throat. A 2022 meta-analysis of 86 trials in people with asthma (Shang and colleagues, Clinical Immunology) found oral or throat candidiasis was about two and a half times as common with long-term inhaled steroids as without them. Clinical guidelines recommend rinsing the mouth after each dose, yet in an Australian survey of 380 inhaler users (Johnstone and colleagues, International Journal of Clinical Pharmacy, 2021) almost a third were not rinsing properly. Rinse with water and spit after every dose. Our article on asthma inhalers and oral health covers the other effects.
Dentures
Yeast grows readily on the fitting surface of a denture, especially one worn day and night. Red, inflamed tissue under an upper denture is often a form of thrush called denture stomatitis. See our guide to denture stomatitis.
Dry mouth
Saliva has natural antifungal properties, so a mouth that is dry from medicines, illness or ageing is more vulnerable. Our guide to dry mouth causes and treatment explains how to manage it.
Diabetes
The NHS lists diabetes among the long-term conditions that raise the risk, and well-controlled blood sugar makes a difference to mouth health more broadly, as covered in diabetes and gum disease.
Lowered immunity
Chemotherapy, long-term steroid tablets, HIV and medicines that suppress the immune system all make thrush more likely, and more likely to be widespread or stubborn.
Clearing it means treating the yeast and the cause
Mild thrush usually responds to an antifungal gel, drops or lozenges, which a pharmacist, dentist or doctor can advise on. Use it for the full time recommended, even after the patches fade, because stopping early invites a relapse. More widespread or stubborn infections, and thrush in people with weakened immunity, may need antifungal tablets prescribed by a doctor or dentist. The NHS advises seeing a GP if there is no improvement after a week of gel treatment.
At the same time, deal with the trigger. Rinse after your puffer. Take dentures out overnight and clean them daily. Look after a dry mouth. Keep diabetes under control. Without these steps, thrush often returns.
A safety warning if you take warfarin
Some antifungals interact with warfarin and can increase bleeding risk. In a Danish study of warfarin users (Iversen and colleagues, American Journal of Medicine, 2021), starting miconazole oral gel was followed by a marked rise in INR, the blood test that measures warfarin's effect, and the share of people with an INR above 5 rose from 5.5% to 30.1%. Fluconazole tablets also raised INR, while nystatin oral solution did not change it. Always tell your dentist, doctor or pharmacist that you take warfarin before using any thrush treatment, and never stop or change your warfarin dose yourself.
Simple habits that help prevent a repeat
- Brush twice a day with fluoride toothpaste and clean between your teeth.
- Rinse with water and spit after using a steroid inhaler.
- Clean dentures every day and keep cleaned dentures in a clean, dry container overnight.
- Sip water through the day if your mouth tends to be dry.
- Keep sugary drinks and snacks to mealtimes.
- Have regular dental check-ups, and have a loose or poorly fitting denture looked at.
When a white patch is not thrush
A white patch that cannot be wiped off may be something else, such as oral lichen planus or leukoplakia or erythroplakia, which need different management. Any white or red patch, sore or lump that has not healed or changed within three weeks should be checked by a dentist or GP. See a dentist or doctor sooner if thrush keeps returning, makes swallowing painful, or appears when you have a condition that weakens your immunity.
Questions about thrush in adults
Is oral thrush contagious?
The NHS states that oral thrush in adults is not contagious. Many people already carry the yeast, and thrush reflects a change in the mouth rather than catching it from someone.
How long does it take to clear?
Mild thrush often settles over several days of treatment once the trigger is dealt with. If it has not improved after a week of gel, the NHS advice is to see a GP, and a dentist can also check for a denture or dry mouth problem keeping it going.
Why does mine keep coming back?
Recurring thrush usually means the trigger is still there: a puffer without rinsing, dentures worn overnight, an untreated dry mouth or blood sugar that is running high. Our related guide on the different forms of oral thrush describes how each type shows up.
If you have sore white or red patches that are not settling, the dentists at Lumi Dental in Melrose Park can examine your mouth, look for the trigger and rule out anything that needs different care. See our current offers or our general dentistry page to book.
