Mouth Sores: Common Causes, Symptoms, & Treatments

By Chesney Fowler, MD
Medically reviewed checkmarkMedically reviewed
July 21, 2020

While any kind of physical pain can be frustrating, mouth sores are especially aggravating because they can interfere with common functions like eating, drinking, swallowing, talking, and breathing. Mouth sores, also known as canker sores or mouth ulcers, cause painful, red lesions on the inside of the mouth.

They may be uncomfortable but mouth sores are generally not harmful, and they typically resolve on their own within a few weeks. Minor mouth sores usually go away within two weeks, and more severe ones can last up to six weeks. While it’s difficult to pinpoint the exact cause of canker sores, some lifestyle factors, like mouth irritation and diet, can contribute.

In some cases, mouth sores can be a sign of another underlying condition. If you have mouth sores that interfere with daily functions, or your mouth sores are getting worse over time, make sure to talk to a doctor to identify the cause and determine the best course of treatment.

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What Are Mouth Sores?

Also known as canker sores or mouth ulcers, mouth sores are round or oval lesions. They can occur on any part of a person’s mouth, including the lips, cheeks, tongue, gums, and roof of the mouth, causing redness and pain. Sometimes, mouth sores can make it hard to eat, drink, or swallow. Canker sores are not contagious.

Mouth sores are generally self resolving, which means they go away on their own. Mouth sores typically go away within 1-2 weeks, or up to six weeks in more severe cases.

In some cases, however, mouth sores can be a sign of another condition, like a viral infection. If you have a mouth sore that’s causing you severe pain, or it’s not going away after a few weeks, make sure to talk to a doctor. The viruses that can cause mouth sores usually are contagious, but not dangerous.

Symptoms of Mouth Sores

If you have mouth sores, you’ll likely feel pain in or around the mouth, often accompanied by redness in the affected area. Other symptoms include:

  • Round sores that are white, yellow, or gray in color with a reddish border
  • Burning or tingling in the affected area
  • Pain that worsens while eating, drinking, swallowing, breathing, or talking
  • Developing painful blisters

In more severe cases, canker sores can result in:

Possible Causes of Mouth Sores

Sometimes, canker sores can be the result of lifestyle or environmental factors. If this is the case, the sores usually resolve when the irritation or environmental change resolves. Common triggers of canker sores include:

  • Biting your tongue, lip, or cheek
  • Burning your mouth
  • Irritation from orthodontia like braces, dentures, or a retainer
  • Injury from a sharp tooth
  • Chewing tobacco
  • Using a firm toothbrush
  • An allergy to toothpaste or mouthwash
  • Acidic foods, like citrus, coffee, chocolate, tomatoes, apples, or pineapples
  • Hormonal changes, such as during the menstrual cycle
  • Stress or lack of sleep

There are also many medical conditions that can cause mouth sores, including bacterial, viral, or fungal infections and other diseases.

Cold sores

Caused by the herpes simplex virus (also known as oral herpes), cold sores are similar to canker sores because they cause red and painful lesions around the mouth. Typically, however, cold sores are fluid-filled, and they appear near the mouth and lips instead of inside the mouth. Cold sores are contagious and spread through personal contact, like kissing.

These sores may also be accompanied by flu-like symptoms, such as:


Another potential cause of mouth sores is leukoplakia, a condition where thick, white, “hairy” patches appear on a person’s tongue. While leukoplakia can be uncomfortable, it’s not usually serious, and it goes away on its own. Leukoplakia is more common in people who smoke, and it can be prevented with routine dental care.

Celiac disease

Celiac disease, an abnormal response of the immune system to gluten, causes damage to a person’s intestinal lining. Ultimately, this damage can impact a person’s ability to absorb essential nutrients, like vitamins B and D. Along with mouth sores, celiac disease can cause symptoms including:


Caused by the Epstein-Barr virus (EBV), mononucleosis is an infectious disease that can cause cold sores. It’s also commonly accompanied by other symptoms, such as:

Oral thrush

Oral thrush, also known as candida, is a fungal infection that develops inside of a person’s mouth, often on the tongue. It most commonly occurs in infants and young children, but immunocompromised adults can also contract it.

Adults with health immune systems usually do not contract thrush, unless they use inhaled steroids to treat conditions such as asthma and COPD. Symptoms of oral thrush may include:

  • Creamy, white bumps that can be scraped off
  • Pain at the site of the bumps
  • Difficulty swallowing
  • Cracked skin in the corners of the mouth
  • Loss of taste

Hand, foot, and mouth disease

Hand, foot, and mouth disease (HFMD) is a viral infection that commonly affects children under the age of five. When it occurs in the mouth, it results in painful, red blisters on the tongue or gums. It can also result in:

  • Raised, red spots or flat spots on the palms or feet
  • Spots on the genital area or buttocks
  • Fever
  • Sore throat
  • Irritability


Gingivostomatitis, an infection of the mouth and gums, can be a result of either a viral or bacterial infection — often, it’s caused by poor dental and oral hygiene. Symptoms may include:

  • Oral or gum swelling
  • Lesions in the mouth that look like canker sores
  • Bad breath
  • Fever
  • Swollen lymph nodes


Rarely, mouth sores can be caused by autoimmune diseases like lupus. Often, lupus mouth sores are red ulcers surrounded by a white border and white, radiating lines. Lupus also causes symptoms like:

  • A butterfly-shaped rash on the face
  • Joint pain
  • Fever
  • Fatigue
  • Skin rashes

Mouth cancer

Oral cancer, a less common cause of mouth sores, can affect a person’s lips, cheeks, teeth, gums, tongue, or mouth. Smoking or chewing tobacco increases your risk of mouth cancer. Symptoms of mouth cancer may include:

  • Red patches or ulcers that appear in the mouth and do not heal
  • Weight loss
  • Bleeding gums
  • Swollen lymph nodes
  • Ear pain
  • Pain while swallowing
  • Coughing

How to Treat Mouth Sores

If you have a canker sore, you can usually expect it to resolve on its own within two weeks—in some more severe cases, however, it may not resolve for six weeks. Fortunately, canker sores are not typically serious, and there are many home remedies for canker sores including:

  • Gargling with salt water
  • Eating cold foods such as ice or popsicles
  • Over-the-counter (OTC) pain medication like ibuprofen or acetaminophen
  • Avoiding hot, spicy, or citrus-based foods
  • Avoiding alcohol and tobacco
  • Applying a thin paste of baking soda and water to the affected area
  • Applying milk of magnesia to the sore
  • Placing a damp, room temperature tea bag on the affected area

If your canker sores are bothering you, ask your doctor or pharmacist about any over-the-counter medications, including mouthwash or toothpaste, that may help.

How to treat other kinds of mouth sores

The best way to treat mouth sores is to treat the underlying cause.

For mouth sores associated with a bacterial or fungal infection, your doctor might recommend an oral or topical antibiotic or antifungal medication, which will help to resolve the infection and the accompanying sores.

For other medical conditions, like celiac disease or mouth cancer, your doctor will work with you to address the underlying issue.

How to Prevent Mouth Sores

The most effective way to prevent canker sores is to avoid common triggers. If you’re prone to mouth ulcers or you want to avoid them, try:

  • Decreasing stress
  • Eating a nutritious, balanced diet
  • Staying hydrated
  • Getting ample sleep
  • Taking a daily multivitamin
  • Eliminating irritating foods, such as spicy foods, coffee, alcohol, or citrus
  • Talking to your dentist or orthodontist if hardware is irritating your mouth
  • Using a softer toothbrush
  • Practicing routine dental hygiene by brushing and flossing
  • Using an SPF lip balm when you’re in the sun
  • Quitting smoking or tobacco products
  • Avoiding foods or drinks that are hot in temperature

Risk Factors and Complications

While doctors aren’t totally sure what causes canker sores, some of the more common risk factors include:

  • Emotional or physical stress
  • Hormonal changes, as in menstruation or pregnancy
  • Deficiencies in folate or vitamin B
  • A weakened immune system due to illness, AIDS, or a recent organ transplant
  • Bacterial, viral, or fungal infections

If you have herpes simplex, you may experience scarring due to severe cold sores. Common risk factors for herpes simplex outbreaks include:

  • Emotional or physical stress
  • A weakened immune system
  • Too much sun exposure
  • Hormonal changes, such as pregnancy or a woman’s menstrual cycle

When to See a Doctor

If mouth sores are causing you pain or interfering with other parts of your life, like eating, drinking, swallowing, talking, or breathing, it’s important to talk to a doctor to determine the root cause and the best course of treatment.

Make sure you consult with a medical professional if you have:

  • Larger mouth sores than usual
  • Mouth sores that last longer than three weeks
  • Pain not relieved by over-the-counter pain medication
  • Major problems with eating, drinking, talking, swallowing or breathing
  • New mouth ulcers that develop before the old ones go away
  • Mouth sores accompanied by a fever or diarrhea

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K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

Chesney Fowler, MD

Dr. Fowler is an emergency medicine physician and received her MD from George Washington University. She completed her residency in emergency medicine at Christiana Care Health System. In addition to her work at K Health, Dr. Fowler is a practicing emergency medicine physician in Washington, DC.