Why Is My Canker Sore Not Going Away? Why It Happens

A canker sore that lingers for weeks is not normal, and it is a signal worth paying attention to. Most canker sores heal on their own within one to two weeks. If yours has been sitting there for three weeks or longer, or if it keeps coming back in the same spot, something else may be going on. Here is what causes canker sores, why some refuse to heal, and when a lingering sore needs a doctor’s eyes.

What Is a Canker Sore, Exactly?

A canker sore is a shallow open ulcer inside the mouth. Doctors call them aphthous ulcers. They are not the same as cold sores, which are caused by a virus and usually appear on or around the lips.

Canker sores form on the soft tissues inside the mouth: the inner cheeks, lips, tongue, floor of the mouth, and sometimes the back of the throat. They typically start as a small red spot or a tingling area. Then a white or yellowish center appears with a red rim around it.

There are three general types:

• Minor — small, under about 1 centimeter, and heal in one to two weeks without scarring. These are by far the most common.
• Major — larger, deeper, and can take several weeks or longer to heal. They may leave a scar.
• Herpetiform — clusters of many tiny sores that can merge into larger irregular patches.

Knowing which type you have matters. A minor sore that suddenly behaves like a major one is a change worth mentioning to a clinician.

Why Is My Canker Sore Not Going Away?

A canker sore that will not heal usually points to one of a few things: ongoing irritation at the site, an underlying health condition, a nutritional deficiency, or a sore that is not actually a canker sore at all.

The most common reason a sore keeps getting re-irritated is mechanical. If a sharp tooth edge, a broken filling, braces, or a denture rubs the same spot every day, the tissue never gets a chance to close. The sore heals a little overnight and reopens by lunch.

Another frequent cause is a condition called recurrent aphthous stomatitis. This is the medical term for getting canker sores again and again. Some people get them a few times a year. Others seem to have one almost constantly. The pattern itself is the diagnosis.

Less often, a sore that will not heal is a sign of something systemic. Conditions that affect the immune system, the digestive tract, or the blood can show up first as mouth ulcers. That is why a sore lasting more than a few weeks deserves a closer look rather than another round of numbing gel.

What Triggers Canker Sores in the First Place?

Canker sores are not caused by a single germ. They are the result of the immune system attacking the lining of the mouth for reasons that vary from person to person.

Common triggers include:

• Minor mouth injury from dental work, hard brushing, sports, or accidental biting
• Certain foods, especially acidic or spicy items like citrus, tomatoes, and chili
• Stress and lack of sleep
• Hormonal changes, particularly around menstruation
• Toothpaste or mouthwash containing sodium lauryl sulfate
• Stopping smoking, which changes the mouth’s lining
• Certain medications

Some of these triggers are well documented. Others are based on patient reports and clinical observation rather than large controlled trials. The sodium lauryl sulfate connection, for example, has been studied but results are mixed. Some people clearly improve when they switch to an SLS-free toothpaste. Others notice no difference.

Which Health Conditions Keep Canker Sores Around?

When canker sores are frequent, slow to heal, or come with other symptoms, a clinician may look for a condition behind them.

Nutritional deficiencies are among the most treatable causes. Low levels of vitamin B12, folate, iron, or zinc have been linked to recurrent mouth ulcers. A simple blood test can check for these. Correcting a deficiency often reduces how often sores appear.

Celiac disease and other digestive conditions can cause recurring mouth ulcers. In some people, mouth sores are one of the first signs, appearing before digestive symptoms.

Crohn’s disease and ulcerative colitis are also associated with mouth ulcers. These are the inflammatory bowel diseases, and they can affect the mouth along with the gut.

Behçet’s disease is a rare condition that causes inflammation throughout the body. Recurring mouth sores are one of its main features. It is uncommon, but it is one reason a doctor may ask about sores in other parts of the body.

Immune system conditions and some blood disorders can also present with persistent mouth ulcers. So can certain infections, including HIV, in some cases.

This list is not meant to alarm. Most people with recurring canker sores do not have any of these conditions. But when sores are severe, frequent, or slow to heal, checking for underlying causes is reasonable.

Could It Be Something Other Than a Canker Sore?

This is one of the most important questions to ask, and it is often overlooked. Not every sore in the mouth is a canker sore.

Cold sores are caused by the herpes simplex virus. They usually appear on the lip or outer edge of the mouth, though they can occur inside. They often start with tingling and form a cluster of small blisters.

Oral lichen planus is a chronic inflammatory condition that can cause white lacy patches or painful red sores inside the mouth.

Oral cancer can appear as a sore that does not heal. This is the reason a mouth sore lasting more than two to three weeks should be examined. Oral cancer sores are often painless at first, which is part of why they get missed. Any sore that persists, especially one that is painless, firm, or growing, needs evaluation.

The key point: a sore that does not heal within two to three weeks should be looked at by a dentist or doctor. This is a widely accepted guideline, and it exists for good reason.

What Actually Helps a Canker Sore Heal?

For minor canker sores, most treatment is aimed at easing pain while the body heals itself. There is no cure that makes a canker sore vanish overnight.

Options that clinicians commonly recommend include:

• Topical gels or creams that form a protective barrier over the sore
• Over-the-counter numbing gels containing benzocaine or similar agents
• Rinses prescribed by a dentist or doctor for more severe cases
• Oral medications for people with frequent or severe outbreaks

Prescription treatments exist for people who get sores often or severely. These include topical corticosteroids and, in some cases, oral medications. These are decisions for a clinician, not something to self-prescribe.

For preventing recurrence, the evidence is strongest for correcting nutritional deficiencies when they are present. Beyond that, avoiding known personal triggers is reasonable, even though it is based more on individual experience than on large trials.

One honest note: many products marketed for canker sores have limited evidence behind them. A product that numbs pain is doing something real. A product that claims to “heal” or “prevent” sores often has little or no clinical trial support. Be skeptical of strong claims.

When Should You See a Doctor About a Mouth Sore?

See a dentist or doctor if a mouth sore lasts longer than two to three weeks, keeps coming back, is unusually large or deep, or comes with fever, weight loss, or sores elsewhere on the body.

Also seek care if the sore is painless. Painless sores are easy to ignore, but they are the ones that most need a professional look.

If you have been diagnosed with a condition linked to mouth ulcers, or if you take medications that can cause them, mention any new or changing sores to your clinician.

Most canker sores are minor and self-limited. The ones that are not deserve attention rather than patience.