How Long Do Canker Sores Last?

If you’ve ever had a painful sore in your mouth, chances are you’ve had a canker sore. These sores can occur anywhere inside your mouth and can make it painful to eat and even talk. 

Read on to learn how long canker sores last, what they look like (with pictures), and what you can do to ease the pain.

What are canker sores?

Canker sores are small, painful sores that can develop on the inside of your mouth. Also called aphthous ulcers, they can develop on any surface of your mouth, including:

• Inner lips

• Tongue

• Gums

• Cheeks

• Roof of the mouth

A canker sore looks like a pale or white circle with a red ring around it. It may turn greyish as it heals. It’s usually small, ranging in size from a pin head to a pencil top eraser. Canker sores usually arise alone but can sometimes occur in a group. In rare cases, canker sores can be very large or deep (10 mm or nearly ½ inch)

They are painful and can cause a burning or stinging sensation, especially when they come in contact with food or even your tongue.

Canker sores aren’t contagious.

What canker sores look like

Here are some pictures of canker sores in different locations.

A large gray-white canker sore on the inside of the lip.

Several canker sores are on the inside of the upper lip.

Multiple canker sores on the lower lip.

A large canker sore on the tongue.

How long do canker sores last?

For most people, canker sores go away on their own in about 1 to 2 weeks. Bigger canker sores may take longer to heal, up to 5 weeks, or more. But large canker sores aren’t common unless you have an underlying medical condition that can cause them (more on that below).  

What are the stages of a canker sore?

A developing canker sore usually follows these stages:

• Prodromal (early) stage: You may notice a tingling or burning sensation in the mouth for 1 to 3 days before the sore develops. Not everyone notices this stage.

• Ulcer stage: A red bump turns into an open sore. The first 3 or 4 days of this stage are usually the most painful, but you may have an open sore for about 1 week.

• Healing stage: The sore gets smaller and less painful. This stage usually takes a few days.  

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• Cold sore vs. canker sore: How do you tell the difference between a cold sore and a canker sore — and which is contagious?

• Is it herpes? Learn the difference between herpes simplex 1 (cold sores) and herpes simplex 2?

What is the fastest way to heal a canker sore?

Canker sores usually heal on their own in about 1 to 2 weeks. But, there are some home remedies and over-the-counter (OTC) treatments that can help them heal faster and reduce the pain. 

Treatments that lessen pain

These topical treatments can help lessen pain: 

• Topical anesthetic: This works by numbing the sore. You apply it directly on canker sores or use it as a rinse and spit it out. One example is benzocaine (Oragel). 

• Coating agent: This adds a soothing coat over the sore. You can combine liquid diphenhydramine (Benadryl) and magnesium hydroxide (Milk of Magnesia) in equal amounts. Swish a teaspoon in your mouth for a minute and then spit it out. 

• Lozenge: Dyclonine lozenges (Sucrets) also numbs your mouth. You dissolve the lozenge slowly in the mouth.

Treatments that may heal canker sores faster

There are some treatments that may help canker sores heal. Many of these will also help lessen pain. 

• Hyaluronic acid: Hyaluronic acid gel protects and hydrates the skin, and also has antioxidant effects. It’s applied directly to the sores.

• Honey: Honey has antibacterial and anti-inflammatory properties. Apply it directly to the canker sores 4 to 5 times a day. 

• Saltwater rinses: Rinse your mouth with a teaspoon of salt mixed in a cup of water. This can help promote wound healing in your mouth. 

If canker sores are large, very painful, or you have many at once, prescription-strength medications may be needed. Some treatments include:

• Numbing agents: Viscous lidocaine can numb the area to reduce pain.

• Oral disinfectant: Chlorhexidine gel can be applied directly to the sores to help prevent secondary infection. 

• Topical steroids: Steroids like triamcinolone paste, dexamethasone elixir, and clobetasol gel or ointment help lower inflammation. Depending on the formulation, these can be applied directly to the sores or used as a rinse. 

• Sucralfate suspension: This is a coating agent that you swish and spit. 

What foods to avoid when you have a canker sore

Any eating can be painful with canker sores. But certain foods may sting or irritate the canker sores more. Try to avoid these foods when the canker sore is in the most painful stages:

• Hard foods like breads, crackers, and pretzels

• Acidic foods like salad dressings or citrus juices

• Spicy foods

• Salty foods like potato chips or ramen

• Hot foods (let it cool off before eating)

• Carbonated drinks

• Alcohol

What triggers a canker sore?

Most of the time, it’s not clear what causes canker sores. They seem to run in families so some people may be more prone to get them. 

Some people find that certain situations seem to trigger them, for example: 

• Stress

• Smoking

• Hormonal changes

• Injury inside the mouth (like from biting your cheek or having dental work)

• Toothpaste with sodium lauryl sulfate

If you get them frequently, they may be a sign of a nutritional deficiency or a symptom of an underlying medical condition. These include:

• Behcet’s disease

• Lupus

• Crohn’s disease and ulcerative colitis

• Celiac disease

• HIV 

• Low iron 

• Low vitamin B12

What can be mistaken for a canker sore?

Canker sores can sometimes be mistaken for cold sores. Cold sores also cause painful sores in the mouth, but they’re not the same thing.  

There are some key differences between canker sores and cold sores:

• Canker sores are usually a white or pale rounded sore with a red border. 

• Cold sores are fluid-filled blisters on a red or dark base. 

• Cold sores can break open and crust, and may occur in groups. 

• Cold sores are caused by the herpes simplex virus (HSV). 

• Cold sores are contagious while canker sores aren’t.

Some other conditions can cause mouth sores that can look like canker sores. But these are much less common:

• Cancer of the mouth

• Lichen planus (a skin rash that can affect the mouth)

• Leukoplakia (white patches caused by smoking and other causes)

When should you see a professional about canker sores?

Some canker sores may need to be seen and treated by a healthcare professional. They can help diagnose any underlying medical condition. And they can prescribe stronger treatments for the pain and to help them heal faster.

Get medical care if you notice any of these symptoms:

• The canker sore lasts more than 2 weeks.

• You’re having a hard time eating or drinking.

• You have a fever, fatigue, or other bodywide symptoms.

• The canker sore is very large or deep.

• You get repeated canker sores.

Frequently asked questions

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Written by:

Maria Robinson, MD, MBA

Maria Robinson, MD, MBA, is a board-certified dermatologist and dermatopathologist who has practiced dermatology and dermatopathology for over 10 years across private practice, academic, and telehealth settings. She is a fellow of the American Academy of Dermatology and the American Society of Dermatopathology.

Edited by:

Laurie Tarkan

Laurie Tarkan is a senior health editor for general health and well-being at GoodRx. She has an extensive background in health journalism, and wrote regularly for The New York Times for a decade.

Reviewed by:

Sophie Vergnaud, MD

Sophie Vergnaud, MD, is the Senior Medical Director for GoodRx Health. An experienced and dedicated pulmonologist and hospitalist, she spent a decade practicing and teaching clinical medicine at academic hospitals throughout London before transitioning to a career in health education and health technology.

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