Mouth sores are any break, irritation, or lesion on the soft tissues inside your mouth, including the lips, cheeks, gums, tongue, and the floor or roof of your mouth. They’re extremely common. About 1 in 5 people experience recurring oral ulcers at some point, with the highest rates in adolescents and young adults. Most mouth sores are harmless and heal on their own within two weeks, but some signal infections, nutritional gaps, or conditions that need attention.
The Most Common Types
Not all mouth sores are the same, and telling them apart matters because the causes and treatments differ significantly.
Canker sores (aphthous ulcers) are the most common type. They appear as small, round or oval sores with a white or yellowish center and a red border. They show up on soft, unattached tissue like the inside of your cheeks, lips, or the underside of your tongue. They’re not contagious, and their exact cause is still unknown. Minor canker sores are typically 2 to 5 millimeters across and heal on their own in 4 to 14 days. Major canker sores, which are 1 to 3 centimeters in diameter, can last 10 days to 6 weeks and sometimes leave scars.
Cold sores (herpes labialis) are caused by herpes simplex virus, most often HSV-1, which has a 60% to 95% prevalence in adults worldwide. Unlike canker sores, cold sores are contagious. They typically appear on or around the lips and sometimes near the nose. They start as clusters of tiny fluid-filled blisters that eventually burst, crust over, and heal. Once you carry the virus, outbreaks can recur throughout your life, often triggered by stress, illness, or sun exposure.
Blisters and erosions from immune conditions are less common but worth knowing about. Autoimmune diseases can cause the body to attack the lining of the mouth, producing fragile blisters that quickly break open into painful raw patches. These tend to persist or keep returning and usually need medical treatment.
What Causes Them
Physical Injury
The most straightforward cause is trauma. Biting your cheek, burning your mouth on hot food, or scraping tissue with a sharp chip or cracker can all produce a sore. Dental work is another frequent culprit. Teeth with jagged edges from decay or fractures, poorly fitting dentures, and braces can all rub against soft tissue repeatedly, creating ulcers that won’t heal until the source of irritation is fixed. These sores most often appear along the edges of the tongue and the inner cheeks.
Infections
Several viruses cause mouth sores beyond herpes. Coxsackievirus is the most common cause of hand, foot, and mouth disease, which produces painful grayish-white blisters that quickly break into shallow ulcers on the soft palate, tonsils, and throat. It usually starts with fever and general malaise before the mouth pain sets in.
Bacterial infections can also be responsible. Syphilis, for example, can produce oral lesions in its secondary stage, appearing as slightly raised, rounded patches covered by a thin pinkish or gray membrane. These lesions can show up on the lips, gums, palate, and tongue. They’re sometimes painless, which makes them easy to overlook.
Nutritional Deficiencies
If you get canker sores frequently, your diet may be a factor. Deficiencies in iron, vitamin B12, folic acid, vitamin B3, and vitamin C have all been linked to recurrent aphthous ulcers. A blood test can identify these gaps, and correcting the deficiency often reduces how often sores come back.
Autoimmune and Chronic Conditions
Recurring mouth sores can be an early or ongoing sign of several systemic diseases. Crohn’s disease, lupus, and HIV are all associated with aphthous-type oral ulcers. Behçet’s disease is particularly notable because painful mouth ulcers are one of its hallmark features. Diagnosis of Behçet’s requires ulcers appearing at two or more sites (mouth, genitals, or eyes) with no other explanation. If you’re getting frequent, severe mouth sores alongside other symptoms like joint pain, skin rashes, or digestive problems, the sores may be pointing to something broader.
Relief and Healing
Most minor mouth sores don’t need treatment. They’ll resolve within one to two weeks. In the meantime, over-the-counter products containing benzocaine can numb the area and reduce pain from eating and drinking. Rinsing with warm salt water several times a day helps keep the sore clean and can ease discomfort.
Avoiding acidic or spicy foods while a sore is active makes a noticeable difference in pain levels. Soft, cool foods are easier to tolerate. If you have a major canker sore that’s interfering with eating or lasting beyond two weeks, a doctor or dentist can prescribe a stronger topical treatment to speed healing.
Reducing How Often They Come Back
One surprisingly effective change is switching your toothpaste. Sodium lauryl sulfate (SLS), the foaming agent in most toothpastes, has been studied for its role in mouth sore recurrence. A systematic review of clinical trials found that people who switched to SLS-free toothpaste had significantly fewer ulcers, shorter healing times, fewer episodes overall, and less pain. If you’re prone to canker sores, this is one of the simplest things to try first.
Beyond toothpaste, managing stress, getting adequate sleep, and ensuring your diet provides enough B vitamins, iron, and folate all help reduce recurrence. If a rough tooth edge or dental appliance is the trigger, getting it smoothed or adjusted eliminates the problem at the source.
When a Mouth Sore Needs Attention
The general rule is that any mouth sore lasting longer than two to three weeks without improvement should be evaluated by a dentist or doctor. This is the timeline that specialists use to distinguish routine sores from something that may need a biopsy. Oral cancers can initially look like a common ulcer, a white or red patch, or a thickened area that doesn’t hurt. The Oral Cancer Foundation recommends prompt referral to a specialist for any oral complaint lasting longer than two to four weeks.
Other signs that warrant a visit: sores that are unusually large, spreading, or accompanied by high fever. Frequent outbreaks (monthly or more) also deserve investigation, since they may point to an underlying deficiency or immune condition that’s treatable once identified.