Canker Sore (Aphthous Ulcer)

Medically Reviewed by Shruthi N on May 23, 2024
Written by Frances Gatta, Kristin Mitchell, WebMD Editorial Contributor
9 min read

A canker sore is a small, shallow, open wound or ulcer in your mouth that can make eating and talking uncomfortable. It is also known as a mouth ulcer or aphthous ulcer. It looks like a white or yellowish open wound with a red border. 

Canker sores may appear on your gums, tongue, mouth roof, or cheek. 

Minor canker sores

Minor canker sores are the most common type of canker sores. These oval-shaped canker sores may appear three or four times a year. They typically happen in people ages 10 to 20. They’re less than 1 centimeter across and heal in about a week without scarring.

Major canker sores

These round-shaped canker sores are less common. The ulcers are bigger and can last from 2 to 6 weeks. They can be painful and often heal with scarring.

Herpetiform canker sores

Herpetiform canker sores usually show up in adulthood. These are rare and show up as clusters of tiny ulcers. You may have 10 to 100 sores in one area. They usually heal in about a week without scarring. Their name may be confusing, but they are unrelated to a herpes virus infection. 

Doctors don’t know what exactly causes most canker sores. 

Things that might cause minor sores include:

  • Stress 
  • Tissue injury, like from a sharp tooth or a dental appliance
  • Certain foods, including citrus or acidic fruits and vegetables (such as lemons, oranges, pineapples, apples, figs, tomatoes, and strawberries)
  • Nonsteroidal anti-inflammatory drugs like ibuprofen
  • An allergy to something in your food, toothpaste, or mouthwash
  • Helicobacter pylori, the bacteria that can cause peptic ulcers

Things that might cause complex canker sores include:

  • A health condition like a weakened immune system, HIV, AIDS, lupus, or Behcet’s disease
  • Nutritional problems like too little vitamin B12, zinc, folic acid, or iron
  • Gut diseases like celiac or Crohn’s

About 1 in 5 people get canker sores regularly. They’re more common in women, possibly because of hormonal differences. They may also run in families.

Are canker sores a type of STD?

No, canker sores aren’t a type of sexually transmitted disease (STD). They’re not contagious either. You can’t spread them in any way, including during kissing. 

Why does someone get multiple canker sores at once?

Most people get two to four canker sores at once. Some may have them again a few weeks after the last ones healed. 

Doctors are unsure why people have multiple canker sores at once. Canker sores may run in families and may be triggered by: 

  • Stress
  • A weakened immune system
  • Hormonal changes
  • Nutritional problems like having low iron or vitamin B 
  • Injury to the lining of your mouth 

Foods that cause canker sores

Foods may cause minor canker sores. These foods are usually acidic.

They include:

  • Carbonated beverages
  • Lemons
  • Oranges
  • Pineapples
  • Apples
  • Figs
  • Tomatoes
  • Strawberries
  • Vinegar
  • Peppermint
  • Grapefruit
  • Berries

Canker sores from dentures

Dentures are artificial teeth used to replace missing teeth. You may have mouth ulcers from wearing dentures if you:

  • Have a candida infection or candida yeast overgrowth
  • Have dentures that aren't fitted properly
  • Wear your dentures for too long 
  • Don’t follow proper oral hygiene
  • Have a diet high in sugars and carbohydrates
  • Smoke or take alcohol
  • Take antibiotics that work against many types of bacteria

You may have a canker sore if you have:

  • A tingling or burning sensation, often 6 to 24 hours before a canker sore
  • Small sores in your mouth that are round or oval, white, gray, or pale yellow with a red edge or border
  • A painful sore or sores that appear alone or in clusters inside your mouth: on your tongue, at the base of the gums, on your soft palate (the back portion of the roof of your mouth), or inside your cheeks
  • A sore that feels worse after eating food that irritates the mouth's lining, like an acidic fruit or spicy food

Severe canker sore attacks may also cause:

  • Fever
  • Fatigue
  • Swollen lymph nodes

Can you get a canker sore on the frenulum?

A frenulum is a rope-like tissue that connects two body parts. You have two in your mouth: one that connects your tongue to the floor of your mouth and another that attaches your lips to your gums. 

You can have a canker sore on the frenulum in your mouth. 

Canker and cold sores aren’t the same. 

Cold sores, also called fever blisters or herpes simplex type 1, are groups of painful, fluid-filled blisters. Unlike canker sores, a virus called herpes causes cold sores, and they’re highly contagious. Also, cold sores typically appear outside your mouth – usually under your nose, around your lips, or under your chin – but canker sores show up inside your mouth.

Unlike canker sores, cold sores cause the skin in the affected area to tighten and spread to areas around it. The blisters in cold sores may also break and ooze fluid when you talk, laugh, chew, or move your lip. 

Are canker sores as contagious as cold sores?

Cold sores are contagious because herpes simplex viruses cause them. Kissing, or other things that cause contact with the blister or fluid, may spread cold sores to others. 

Canker sores are not contagious because they’re not caused by a virus or other types of infectious agents. 

You can tell if you have a canker sore by how it looks and how painful it is. Call your doctor or dentist if you have:

  • Unusually large sores
  • Sores that spread
  • Sores that last 2 weeks or longer
  • Extreme pain despite avoiding trigger foods and taking over-the-counter pain medication
  • Trouble drinking enough fluids
  • A high fever with canker sores
  • Frequent or lasting mouth sores, which may be a sign of problems such as a serious skin disorder called pemphigus, celiac disease, inflammatory bowel disease, Behcet's disease, an autoimmune disease, anemia, or HIV. In rare cases, they may be a sign of oral cancer or leukemia.

Doctors can usually diagnose your condition by doing a physical exam and looking at your medical history. They will look at the lining of your mouth and ask about your symptoms and how you’ve been eating.

They might also do a blood, swab, or tissue sample test to see whether a lack of vitamins or another health condition is causing the sores.

 

Pain from a canker sore tends to ease in a few days, and the sores usually heal without treatment in about a week or two. Treatment for large, long-lasting, or unusually painful sores might include:

  • Mouthwashes. Your doctor can prescribe a rinse that has a steroid or a painkiller.
  • Topical medications. Your doctor may prescribe one that has a steroid for inflammation and a topical analgesic like lidocaine to relieve pain. Triamcinolone acetonide or clobetasol are often used to reduce pain and inflammation from canker sores.
  • Oral medications. The ulcer drug sucralfate (Carafate) and the gout drug colchicine (Mitigare) can also treat canker sores. Or your doctor might give you steroid pills.
  • Nutritional supplements. You might need these if a lack of nutrients is causing your canker sores.   
  • Cautery. Dental lasers can help you feel better right away. Your doctor can also cauterize sores with chemicals like Debacterol or silver nitrate.

How long do canker sores last?

Canker sores usually last for about a week. It can take up to 4 weeks for major canker sores to go away.

How to treat canker sores on the tongue

You can treat canker sores on the tongue by 

  • Rinsing your mouth with warm salt water or other gentle over-the-counter mouth rinses a few times every day
  • Practicing proper oral hygiene by brushing with a soft-bristled toothbrush and flossing
  • Drinking enough water every day
  • Limiting how much hot, spicy, and acidic food you have
  • Taking medications your doctor prescribes for the canker sore

Home treatments that may help to speed healing and help you feel better include:

  • Topical products. Medicated gels, creams, pastes, and liquids go on the sore.
  • Mouth rinses. Mix salt or baking soda in warm water and swish it around your mouth.
  • Milk of magnesia. Put a bit on a cotton swab and dab it on the sore.

What's the best home remedy for canker sores on the gum?

You can try to manage canker sores on the gum at home by rinsing your mouth a few times a day with: 

  • Salt water
  • Over-the-counter mouthwashes that don’t have alcohol
  • An over-the-counter numbing mouth rinse
  • Or a mixture of milk of magnesia and Benadryl liquid medicine

Aloe vera and canker sores

Putting aloe vera on your canker sore may reduce pain and the size of your ulcer and help it heal faster. You can put the gel on the sore or take aloe vera juice. 

Honey for canker sores

Some research has shown that honey can make your canker sore feel less painful and heal it. You can put honey on the sore and surrounding areas to try to relieve your symptoms.

Canker sores may come back frequently. But you can prevent canker sores from happening often if you:

  • Avoid foods that irritate your mouth, including acidic fruit and vegetables and spicy foods.
  • Don’t chew gum.
  • Brush your teeth with a soft-bristled brush, and floss, keeping your mouth free of foods that might trigger a sore.
  • Eat a healthy, balanced diet.

Can you kiss someone with a canker sore?

Canker sores might make kissing a bit uncomfortable. But if the person feels comfortable and agrees to kiss you, kissing is okay.

Canker sores form a shallow, painful, and inconvenient ulcer in your mouth. But they usually go away on their own within a few days. You can also try over-the-counter mouth rinses, salt water, honey, and aloe vera to relieve pain and speed up the healing process. Remember to maintain oral hygiene by brushing your teeth and flossing. See a doctor if your canker sores don’t go away after 2 weeks.

What is the best medication for canker sores? Medicines you put on the sore with the active ingredients benzocaine, fluocinonide, or hydrogen peroxide can help treat canker sores. 

What is the fastest way to cure a mouth ulcer? The fastest way to treat a mouth ulcer is by rinsing your mouth with warm salt water. 

What is the difference between a regular canker sore and a complex canker sore? Regular canker sores are small, shallow ulcers that usually go away on their own in a few days to 2 weeks. 

Complex canker sores, on the other hand, are bigger and more painful mouth ulcers that may take up to 6 weeks to heal. They may happen when you have a weakened immune system, nutritional problems, or stomach conditions like celiac disease. See a doctor if you have this kind of canker sore, as they can let you know why you might have it and recommend treatment. 

How can you get rid of a canker sore in 24 hours? You can treat canker sores with mouth rinses and medicines you apply to the sore. They may go away in 24 hours, and if not, in a few days, for minor canker sores. 

What's at the center of a canker sore? The whitish middle of a canker sore is made of fibrin (a protein involved in blood clotting) and inflammatory cells. It’s part of the healing process and protects the tissue beneath it.