Oral thrush is a fungal infection that develops inside the mouth, on the tongue, and in the throat. It is caused by an overgrowth of a yeast called Candida albicans. Oral thrush can affect Canadians at any age, from newborns to older adults. In this article, we explain what causes it, what symptoms to watch for, and how it is treated.
What Is Oral Thrush?
Oral thrush — also called oral candidiasis — is a fungal infection caused by Candida yeast. Small amounts of this yeast live naturally in your mouth without causing any harm. However, when something disrupts the balance of bacteria and yeast in your mouth, Candida can multiply out of control.
The infection is most common in newborns, infants, and older adults. It also affects people with weakened immune systems. In healthy babies, oral thrush is usually mild and clears up quickly with treatment.
What Causes Oral Thrush?
Oral thrush develops when the natural balance of microorganisms in your mouth is disturbed. Several factors can allow Candida yeast to grow unchecked. The most common cause is Candida albicans, but other species — such as Candida tropicalis and Candida glabrata — can also be responsible.
The following factors increase your risk of developing oral thrush:
Weakened immune system: Conditions like HIV/AIDS significantly raise your risk. In fact, roughly 90% of people living with HIV develop oral thrush at least once.
Diabetes: High blood sugar levels encourage yeast to grow. People with poorly controlled diabetes are especially vulnerable.
Antibiotics: Broad-spectrum antibiotics (such as tetracycline) kill helpful bacteria in your mouth. This disruption allows yeast to overgrow.
Corticosteroids: Inhaled or oral corticosteroids lower your immune defences, making it easier for thrush to take hold.
Oral contraceptives: Hormonal changes from birth control pills can alter the balance of microorganisms in your mouth.
Dry mouth (xerostomia): Reduced saliva — whether from overusing mouthwash or from conditions like Sjögren’s syndrome — creates an environment where yeast thrives.
Pregnancy: Hormonal shifts during pregnancy can disturb the microbial balance inside the mouth.
Poor oral hygiene: This is especially a concern for people who wear dentures.
According to Health Canada, maintaining good oral hygiene and managing underlying health conditions are key steps in reducing your risk of fungal infections like oral thrush.
How Does Oral Thrush Spread?
The way oral thrush spreads depends on a person’s age. Understanding transmission helps prevent the infection from passing between family members.
In Newborns and Infants
A newborn can pick up Candida from their mother during vaginal delivery if the mother has a vaginal yeast infection. Symptoms in the baby typically appear within three to seven days of birth. Infants are more vulnerable because their immune systems are not yet fully developed, and the balance of microorganisms in their mouths is still being established.
In addition, a baby with oral thrush can pass the yeast to their mother’s nipples during breastfeeding. This can cause sore, red nipples for the mother — especially during or after feeding.
In Children and Teenagers
Oral thrush is generally not contagious in healthy children. However, children with weakened immune systems can sometimes pick up the infection from shared toys or close contact with other children. Any toy placed in an infected child’s mouth can carry the yeast.
In Adults
In adults, oral thrush can spread through oral sexual contact. It is worth noting that vaginal yeast infections are caused by the same Candida fungus responsible for oral thrush.
Symptoms of Oral Thrush
Mild cases of oral thrush may cause no symptoms at all. More moderate or severe cases produce noticeable signs that can affect eating and daily comfort.
Symptoms in Babies
Oral thrush in babies can sometimes be confused with leftover milk in the mouth. However, there are clear differences. Look for these signs:
White, cottage cheese-like patches on the inside of the mouth and tongue. Unlike milk residue, these patches stick firmly to the lining of the mouth and may bleed slightly if you try to wipe them away.
Sore mouth and difficulty swallowing, which can make feeding painful.
Poor appetite or refusal to feed. Your baby may pull away during breastfeeding or seem unusually fussy. This can easily be mistaken for fullness.
Diaper rash, which can develop when the Candida infection spreads through the digestive tract and appears in the baby’s stool.
If you notice your baby refusing to feed alongside white patches in their mouth, contact your family doctor or visit a walk-in clinic promptly.
Symptoms in Adults
Adults with oral thrush often notice the following:
A burning sensation in the mouth or throat. This is often one of the earliest symptoms.
White, raised patches on the tongue, inner cheeks, gums, or throat. The tissue surrounding these patches is usually red and sore.
Bleeding when the patches are rubbed — for example, during tooth brushing.
A loss of taste or an unpleasant taste in the mouth.
For more detailed information on symptoms and diagnosis, the Mayo Clinic’s oral thrush resource offers a thorough overview.
Treatment for Oral Thrush
Most cases of oral thrush respond well to antifungal treatment. The approach depends on the severity of the infection and the patient’s overall health.
Mild to Moderate Cases
For mild oral thrush, a doctor will typically prescribe a topical antifungal medication. This is applied directly inside the mouth as a liquid or lozenge. Treatment usually lasts up to 14 days. Very mild cases may even clear up on their own, though it is always best to check with a healthcare provider.
Severe or Recurring Cases
When oral thrush is severe or keeps coming back, a doctor may prescribe oral antifungal tablets. These work throughout the body to eliminate the infection. In some cases, thrush may persist for several weeks even with treatment, particularly in people with weakened immune systems.
For Breastfeeding Mothers and Babies
Both the mother and the baby need to be treated at the same time. This prevents the infection from passing back and forth during breastfeeding. Your family doctor or a public health nurse can guide you through safe treatment options.
Helpful Home Habits
Alongside medical treatment, these habits can help your recovery and prevent oral thrush from returning:
Brush your teeth gently twice a day and rinse your mouth with water after using a corticosteroid inhaler.
Avoid using antibacterial mouthwash too often, as it can disrupt the natural balance in your mouth.
If you wear dentures, clean them thoroughly every day and remove them at night.
Manage underlying conditions like diabetes by keeping your blood sugar within a healthy range.
Eat plain yoghurt containing live bacterial cultures, which may help restore healthy microbial balance.
Healthline’s guide to thrush treatment also outlines several evidence-based strategies for managing and preventing this infection.
When to See a Doctor
Oral thrush is treatable, but it is important to get a proper diagnosis. Do not try to self-diagnose or treat oral thrush on your own without speaking to a healthcare professional first.
You should contact your family doctor or visit a walk-in clinic if:
You or your baby has white patches inside the mouth that do not wipe away easily.
Your baby is refusing to feed or seems unusually irritable.
You have a burning sensation in your mouth that does not go away within a few days.
Your symptoms do not improve after starting treatment.
You have a condition that weakens your immune system, such as HIV, cancer, or uncontrolled diabetes.
You are pregnant and notice any signs of oral thrush.
In Canada, most provincial health plans cover visits to your family doctor or a walk-in clinic for infections like oral thrush. If you are not sure where to go, call your provincial health line — such as Ontario’s Telehealth Ontario or BC’s HealthLink 811 — for guidance from a registered nurse.
Always consult your doctor or a qualified healthcare provider before starting any treatment. This article is for informational purposes only and does not replace professional medical advice.
Frequently Asked Questions About Oral Thrush
Is oral thrush contagious?
Oral thrush is generally not contagious in healthy people. However, it can spread between a breastfeeding baby and their mother. Children or adults with weakened immune systems may also be more susceptible to picking up the Candida yeast through close contact.
How long does oral thrush last?
With proper antifungal treatment, mild oral thrush often clears up within one to two weeks. More severe cases can persist for several weeks, even with medication. If your symptoms are not improving after two weeks of treatment, speak with your family doctor.
Can oral thrush go away on its own?
Very mild cases of oral thrush may resolve without treatment, particularly in otherwise healthy adults. However, it is always safer to consult a doctor, because untreated oral thrush can spread and become more difficult to treat. Babies and people with weakened immune systems should always receive medical care.
What does oral thrush look like?
Oral thrush appears as creamy white or yellowish patches on the tongue, inner cheeks, gums, or throat. The patches look similar to cottage cheese and may bleed slightly when wiped. The surrounding tissue is usually red and sore.
Can antibiotics cause oral thrush?
Yes. Antibiotics — especially broad-spectrum types — kill helpful bacteria in your mouth along with harmful ones. This disruption allows Candida yeast to grow unchecked, leading to oral thrush. If you develop white patches in your mouth while taking antibiotics, contact your doctor or visit a walk-in clinic.
How is oral thrush treated in Canada?
In Canada, oral thrush is typically treated with prescription antifungal medications, either as a topical rinse or lozenge applied directly in the mouth, or as oral tablets for more severe cases. Your family doctor or a walk-in clinic physician can assess your symptoms and recommend the right treatment. Most provincial health plans cover this type of visit.
Key Takeaways
Oral thrush is a fungal infection caused by an overgrowth of Candida yeast in the mouth.
It is most common in newborns, infants, older adults, and people with weakened immune systems.
Common risk factors include antibiotic use, diabetes, corticosteroids, dry mouth, and poor oral hygiene.
Key symptoms include white, cottage cheese-like patches in the mouth, a burning sensation, and difficulty swallowing.
Most cases respond well to antifungal treatment prescribed by a doctor, lasting up to 14 days.
If you or your baby shows signs of oral thrush, see your family doctor or visit a walk-in clinic for proper diagnosis and treatment.
Good oral hygiene and managing underlying health conditions are the best ways to prevent oral thrush from recurring.
