Canker Sore Won’t Heal

My canker sore won't go away!

Canker sores are small, painful sores that appear in your mouth. In general, canker sores clear up by themselves after a week or so and can be managed at home. However, sometimes you can get a canker sore that won't heal.

If you have a canker sore that won't heal, don't ignore it. It may just be a stubborn sore, but it could be a more serious condition, such as oral cancer or another life-threatening illness.

Who gets stubborn canker sores?

If you don't fall into the categories below, it could indicate that your persistent canker sore is not normal. Keep in mind that anyone can get a canker sore.

However, here are the normal trends:

  • Women get RAS more often than men, especially in their 20s.
  • Scientists are researching whether chronic canker sores could be influenced by genetics.
  • Some people who get recurring canker sores have a family history of canker sores.

Once a canker sore is noticeable inside your mouth, the pain typically lasts about 10 days. However, it can take another two weeks to heal. Under normal circumstances, cankers sores heal on their own, unless you're sick or have a compromised immune system that interferes with the healing process. Larger ulcers take longer to dissipate.

What does a canker sore look like?

Most canker sores are round or oval in shape and appear on the inside of the lips, cheek or tongue. They are swollen and painful and are usually red, yellow, white or gray in color.

Canker sores usually clear up by themselves within a week or two, but if they hang around for longer than this or if you repeatedly get them, you should see your doctor.

What causes canker sores?

Most canker sores are caused by accidentally biting the inside of the mouth, lip or tongue. Poorly fitting dentures, a defective filling or a very sharp tooth can also be responsible.

Other causes of canker sores include:

  • Stress
  • Hormonal changes
  • Eating foods that are very spicy, salty or acidic
  • Using toothpaste that contains sodium lauryl sulphate
  • Quitting smoking
  • Genetics

In addition, there are some medical conditions that can predispose to developing a canker sore that won't go away. These conditions include viral infections such as chicken pox, and hand, foot and mouth disease.

Deficiencies in iron and vitamin B12 can cause canker sores to erupt, as can Crohn's disease, Celiac disease, reactive arthritis, HIV or lupus.

Canker sore development

To help determine whether your persistent canker sore poses a serious health threat, it's helpful to recall what may have caused it to appear.

Here's what typically happens:

  1. Before you get a canker sore, the area feels itchy or burns.
  2. A few days later, you may notice a small bump in the area that has become inflamed. Over time, it becomes extremely painful to eat or drink certain foods and beverages.
  3. If you have a dry mouth, the pain is likely to be worse.

In contrast, as stated above, cancer looks different and isn't usually immediately painful. However, don't self-diagnose your canker sore, especially if it's been hanging around and not getting any better.

How to treat stubborn canker sores

Canker sores can be very painful and can make eating and drinking difficult.

Here are a few things that you can do if your canker sore won't heal:

  1. Ask your pharmacist for a protective, painkilling paste, spray or gel and apply this to the sore, following the manufacturer's directives.
  2. Change your toothbrush for a very soft one and use toothpaste that does not contain lauryl sulphate, which may irritate your mouth.
  3. Avoid eating spicy, acidic or hard foods until the sore heals.
  4. Stick to cool drinks and use a straw so that you can bypass the sore.
  5. Use antibacterial mouthwash to prevent the sore from becoming infected.
  6. Over-the-counter corticosteroid lozenges can be helpful in reducing pain and accelerating healing. Use these as soon as the canker sore appears. If these aren't effective, your doctor can prescribe you something stronger.

What if my canker sore doesn't heal in two weeks?

If your canker sore isn't better after two weeks, you should see a doctor or dentist. They may prescribe medicine to help relieve the pain caused by canker sore.

The medicine will most likely be applied in one of the following ways:

  • A prescription mouthwash that's gargled or swished in your mouth
  • A steroid cream or paste to paint on the sore

If you have a fever or trouble swallowing, tell your doctor. If your canker sores are chronic, don't go away or keep coming back, there could be larger problems going on.

What if I get a fever with my canker sore?

Getting a fever from your canker sore may not mean anything special, particularly if you are already sick when the sore appears. Fevers are somewhat common if you have three or more sores. You can also experience swollen lymph nodes as your body fights to heal the sore and any resulting infection.

As a rule of thumb, once the canker sore turns whitish-gray, the coagulants and healing proteins in your mouth have begun to repair the lesion.

What about oral cancer?

Oral cancer is a potentially fatal disease that affects the mouth, throat, tongue and lips.

The symptoms of mouth cancer include:

  • Lumps in your jaw or neck area (possibly caused by swollen lymph nodes)
  • Red or white patches on your tongue or inside your mouth
  • Hoarseness in your voice that persists with no obvious cause, such as a cold or throat infection
  • Canker sores that do not heal within a few days
  • Pain in your mouth that won't go away
  • Weight loss with no obvious explanation
  • Pain or difficulty when moving your jaw
  • Teeth that become loose for no obvious reason

Difference between canker sores and mouth cancer

It can be difficult to tell whether your canker sore is oral cancer.

Here are a few things to indicate whether you may have oral cancer:

  • Mouth cancer impacts your lips, throat, tongue or cheeks.
  • Flat, white patches on these areas may indicate cancer or contain cells that lead to cancer.
  • Mixed red and white areas or bright red patches are not a good sign.
  • Mouth cancer can occur in rough patches that are difficult to remove.

Although these symptoms can be benign, you should always ask a dentist to take a look, in case there is a larger problem. According to, if you have painless canker sores that aren't healing, this can indicate mouth cancer. The American Dental Association recommends making an appointment to check out your ulcers if any mouth cancer signs or symptoms last more than two weeks.


It's a good idea to ask your dentist to carry out screening for oral cancer when you attend the dental clinic or dental hospital for your routine annual dental check-up, especially if you habitually suffer from canker sores.

The dentist will carry out a thorough and detailed examination of all the structures in your mouth, including your tongue and lips. If you wear dentures, you will be asked to remove them so that the dentist can examine your gums beneath the dentures.

Some dental hospitals also have special light-emitting tools that allow the dentist to see deeper into the soft tissues of the palate where any abnormalities or suspicious lesions within the mucosa will be highlighted. If any areas of concern are identified, the dentist may use a specialized brush to remove layers of the epithelium in a quick and painless procedure. This procedure is usually carried out if there are areas of unusual coloration present inside your mouth.

The tissue samples will be sent off to an oral cytopathology specialist for examination under laboratory conditions. If cancerous cells are found to be present, you will be referred to an oncology specialist for treatment.

Recurrent aphthous stomatitis

Chronic canker sores are medically known as recurrent aphthous stomatitis (RAS).

These stubborn open sores can be found:

  • On the gums
  • Under the tongue
  • Inside the mouth on the cheek area
  • More rarely, at the back of the throat

Aphthous ulcers (canker sores) occur when the mucous membrane in your mouth breaks open, leaving behind a painful lesion. Since research hasn't discovered the root cause of the lesions, prevention can be difficult if you are prone to get them.

However, even chronic canker sores aren't contagious. As a matter of fact, canker sores have no relation to cold sores or fever blisters caused by the herpes simplex virus. Cold sores and fever blisters always occur outside the mouth, whereas canker sores occur inside the mouth.

Research regarding chronic canker sores

A team of oral pathologists conducted a study among people with chronic canker sores. They each had suffered at least 3 episodes of recurrent aphthous stomatitis. They published the results under the title "Reduced dietary intake of vitamin B12 and folate in patients with RAS."

Published in the Journal of Oral Pathological Medicine, the study results concluded that these patients with chronic canker sores had a statistically significant deficiency of dietary B12. This points to a deficiency of the folate B12 as one possible trigger for chronic canker sores.

Taking a B12 supplement might reduce the occurrence of canker sores for individuals who are prone to them and don't get enough B12 in their normal diet.

When to see a doctor about chronic canker sores

Most canker sores heal in two weeks. So, few people have to visit a doctor for them.

Here are some examples of abnormal lesions that can be a sign of serious illness:

  • Your canker lesion becomes acutely painful, grows larger than a dime or has an asymmetrical shape
  • You get a fever every time the canker sores return
  • It doesn't heal by itself within four weeks
  • A large cluster of sores impacts one area inside your mouth
  • If cankers sores spread from inside to outside of your lips

Preventing chronic canker sores

In order to prevent canker sores from lingering longer and continually coming back:

  • Practice good oral hygiene by brushing your teeth and flossing regularly
  • Eat a diet high in B12, iron, and folate
  • Stress impacts your body in many ways, and reducing stress can contribute to the prevention of persistent canker sores
  • Most importantly, buy toothpaste free of sodium lauryl sulfate (SLS), which can irritate the mouth and contribute to canker sore severity.

NOTE: Sodium lauryl sulfate (SLS) is a detergent also used in soap and shampoo. When you brush with toothpaste containing SLS, it causes early canker sores to get worse and may promote larger lesions for those who have RAS. SLS doesn't improve oral hygiene, but its foaming action makes consumers believe it's performing a vital task.


With pemphigus, your immune system creates antibodies that attack proteins your cells need to stick together. Consequently, this forces your cells to separate or become unglued. Fluid collects between the layers of skin in your mouth, forming blisters. When these blisters rupture, the fragile top layer of skin opens to create an open sore.

Of all the various types, pemphigus vulgaris is most common. If you have pemphigus vulgaris, you usually get the first blister in your mouth. As the disease progresses, blisters can rupture in the mucous membranes in other areas of the body – eyes, nose, throat, and genitals. Pay attention to whether you experience these symptoms when you get a canker sore that won't go away.

Who gets canker sores that indicate pemphigus?

Pemphigus is seen most frequently in the following people:

  • Middle-aged adults
  • Senior citizens
  • Women are slightly more apt than men to get it
  • If you are Mediterranean, Middle Eastern or Ashkenazi Jewish, you are more susceptible.

Getting help

A dermatologist or ear, nose and throat doctor who has experience dealing with persistent canker sores and pemphigus can help. Before the medicine progressed, Pemphigus patients typically died. Their mucous membranes and skin constantly erupted until fatal infection developed. Today, medications can help victims heal and recover.

Options include:

  • Corticosteroids (such as prednisone)
  • Oral immunosuppressants such as mycophenolate mofetil (CellCept)

Biological therapies include:

  • Rituximab (Rituxan) targets the white blood cells that make antibodies
  • Antibiotics can battle infections

As with oral cancer, pemphigus is chronic, and requires regular care. If you develop it, you will need to maintain a careful medical regime for the rest of your life.

Your doctor may prescribe supplements to counteract the side effects of the potent medicines used to treat pemphigus.

Supplements include:

  • Calcium with vitamin D to help for steroid
  • Probiotics if you take antibiotics

Herpetiform ulceration

A long-lasting canker sore that doesn't go away could also be herpetiform ulcers, also called stomatitis herpetiformis, which means herpes-like lesions. They look like the lesions that develop from a herpes simplex virus. However, herpetiform ulceration is not caused by the herpes virus. It's not contagious, unlike true herpes. (If your canker sore is preceded by tiny, fluid-filled blisters, you should get tested for the herpes virus.) Herpetiform ulcers are about one millimeter across, much smaller than normal canker sores. They occur in clusters of up to one hundred.


Stubborn canker sores can be a real pain – literally. If your canker sore won't heal and hangs around for more than three weeks or if you suffer from repeated sores, you should consult your doctor or dentist to treat the underlying cause and rule out anything more serious.

Last Reviewed:
June 13, 2017
Last Updated:
October 04, 2018
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