Most mouth ulcers heal on their own within two weeks. If yours has lasted longer than that, something is either preventing normal healing or the ulcer isn’t the common type you think it is. The causes range from simple mechanical irritation to nutritional deficiencies, medication side effects, and, less commonly, conditions that need medical attention.
How Long a Normal Mouth Ulcer Takes to Heal
Standard canker sores (aphthous ulcers) are typically smaller than a pea and resolve within two weeks without treatment. Even the cluster-type canker sores, where several tiny ulcers appear together, follow roughly the same timeline. Ulcers caused by biting your cheek or burning your mouth on hot food usually stop hurting within three days once the source of irritation is gone, and close up within ten days.
Two weeks is the dividing line clinicians use to separate routine ulcers from ones that need investigation. If your ulcer has been present for more than two weeks, that alone is enough reason to have it looked at. A biopsy or referral may be appropriate, because most self-limiting conditions resolve within that window.
Something Keeps Irritating the Spot
The most overlooked reason a mouth ulcer won’t heal is ongoing physical trauma. A sharp tooth edge, a misaligned bite, a rough spot on a denture or retainer, or even a habit of chewing the inside of your cheek can reinjure tissue every time you eat or talk. The ulcer starts to heal, gets damaged again, and the cycle repeats for weeks or months.
In some cases, chronic irritation triggers a specific type of slow-healing lesion that can persist for much longer than a normal sore. These lesions tend to develop raised or rolled borders and can look alarming, sometimes even mimicking something more serious. They’re most common in adults over 40 and are strongly linked to missing teeth, mispositioned teeth, or ill-fitting dental appliances. Removing the source of irritation is usually enough for healing to begin, but a biopsy is often needed first to rule out other causes.
Nutritional Deficiencies That Stall Healing
Your body needs certain nutrients to maintain and repair the lining of your mouth. When those run low, ulcers can appear out of nowhere and take much longer to close. The three most common culprits are vitamin B12, folate, and iron.
B12 deficiency in particular is known to cause recurrent mouth ulcers, along with a sore or swollen tongue, burning sensations, and changes in taste. These oral symptoms can actually show up before any blood-related signs like fatigue or weakness, which means your mouth may be giving you the earliest warning. B12 deficiency sometimes stems from an autoimmune condition called pernicious anemia, where the stomach gradually loses its ability to absorb the vitamin. A simple blood test can check your levels.
Iron deficiency works similarly. Low iron impairs the turnover of cells lining your mouth, leaving tissue fragile and slow to repair. If you’ve noticed ulcers alongside fatigue, pale skin, or feeling cold easily, iron levels are worth checking.
Medications That Cause Mouth Ulcers
Several types of medication can cause or prolong oral ulcers as a side effect. Anti-inflammatory painkillers (NSAIDs like ibuprofen or naproxen) are among the most common offenders, especially when used frequently. Other drug classes linked to mouth ulcers include certain blood pressure medications, heart medications, immune-suppressing drugs, and some antibiotics.
If your ulcer appeared or worsened after starting a new medication, that timing matters. Don’t stop any prescribed medication on your own, but do mention the connection to your doctor or pharmacist. In many cases, switching to an alternative resolves the problem.
Gut Conditions That Show Up in Your Mouth
Recurrent mouth ulcers that keep coming back or refuse to heal can be an early sign of celiac disease or inflammatory bowel disease. In one large study, nearly 23% of people with celiac disease had recurring mouth ulcers, compared to just 7% of people without the condition. That made recurrent oral ulcers roughly four times more likely in celiac patients. Importantly, switching to a gluten-free diet led to improvement in the ulcers, which supports the connection.
The mechanism is straightforward: these conditions impair nutrient absorption in the gut, creating the same B12, folate, and iron deficiencies described above. They can also drive inflammation that directly affects oral tissue. If your mouth ulcers come with digestive symptoms like bloating, diarrhea, or unexplained weight changes, it’s worth discussing screening for celiac disease or Crohn’s disease with your doctor.
Behçet’s Disease and Other Systemic Causes
Behçet’s disease is an uncommon inflammatory condition where recurrent mouth ulcers are often the very first symptom, appearing in 50 to 70% of cases before any other signs develop. Eventually, up to 98% of people with Behçet’s develop oral ulcers. The sores tend to appear in crops, are painful, and typically last two to three weeks before resolving, only to return at unpredictable intervals.
What distinguishes Behçet’s from ordinary canker sores is the pattern: frequent recurrence combined with other symptoms like genital ulcers, skin lesions, eye inflammation, or joint pain. If you’re experiencing mouth ulcers alongside any of these, it’s a combination worth bringing to a doctor’s attention.
When an Ulcer Could Be Something More Serious
A persistent, non-healing mouth ulcer is one of the most common presentations of oral cancer, specifically squamous cell carcinoma. Many cases are initially misdiagnosed as ordinary sores, sometimes for months before the correct diagnosis is made.
There are specific features that distinguish a concerning ulcer from a benign one. A cancerous ulcer typically has rolled, firm (indurated) borders and a velvety base, creating a crater-like appearance. It is often painless, which is counterintuitive but important: the lack of pain means people tend to ignore it longer. It can appear anywhere in the mouth but is particularly concerning on the side or underside of the tongue.
Risk factors include tobacco use, heavy alcohol consumption, HPV infection, and prolonged sun exposure (for lip lesions). But oral cancer can also occur in people with none of these risk factors. The key warning sign is simply duration: an ulcer that doesn’t heal within two weeks, regardless of what it looks like, deserves professional evaluation. Ulcers on the side of the tongue that come with pain, numbness, raised borders, difficulty swallowing, or unexplained bleeding should be assessed promptly.
What Treatment Looks Like
For persistent canker sores that aren’t caused by an underlying condition, topical treatments are the first-line approach. Prescription-strength options include steroid pastes (like triamcinolone acetonide) and anti-inflammatory gels (like amlexanox), both of which have been shown to significantly reduce ulcer size, pain, and redness within 8 to 10 days in clinical trials. They work by calming the inflammatory response that keeps the ulcer active.
Over-the-counter numbing gels containing benzocaine can help with pain but are less effective at speeding actual healing. For ulcers that recur frequently, an antibiotic rinse mixed into a paste may help by reducing bacterial activity in the wound. In all cases, topical treatments remain the preferred starting point because they’re effective, affordable, and carry fewer side effects than systemic medications.
If your ulcer is caused by a nutritional deficiency, treating the deficiency resolves the ulcers. B12 replacement, whether through injections or high-dose supplements, typically leads to improvement in oral symptoms. If a dental irritant is the cause, smoothing a rough tooth edge or adjusting a denture is often all that’s needed.
What Happens at a Medical Evaluation
If you visit a dentist or doctor about a non-healing ulcer, they’ll examine the sore’s size, location, border texture, and color. They’ll ask how long it’s been there, whether it’s painful, and whether you’ve had similar sores before. Blood tests may be ordered to check for nutritional deficiencies or markers of autoimmune conditions.
A biopsy, where a small sample of tissue is taken from the ulcer, is the definitive way to determine what’s going on. Clinical guidelines recommend considering biopsy for any oral lesion present for more than two weeks, and particularly for ulcers with raised borders, unusual coloring, or location on the side of the tongue. The procedure itself is quick and done under local anesthesia. If your practitioner isn’t experienced with the specific site, they’ll typically refer you to an oral surgeon or specialist.