Why Do I Keep Getting Canker Sores?

Canker sores often keep coming back because several factors overlap: small injuries inside the mouth, stress, certain foods, a family tendency, low iron, vitamin B12 or folate, and sometimes an underlying condition such as celiac disease. Most are painful but heal on their own. Sores that are very frequent, unusually large, slow to heal, or paired with fever, skin changes or weight loss deserve a clinician's evaluation. This article covers common contributors, look-alikes, evaluation and everyday care.

Why canker sores keep coming back

Canker sores are also called aphthous ulcers. They are shallow, round or oval sores with a white or yellow center and a red edge, found on the soft tissue inside the mouth: the inner lips, cheeks, tongue and floor of the mouth. When they return again and again, clinicians call the pattern recurrent aphthous ulceration. A recent NIH-hosted research article on recurrent aphthous ulcerations describes how these ulcers are identified from clinical images of the mouth, which reflects how often they are seen in practice.

The mechanism is not fully understood. Current thinking is that several factors contribute, and the immune system in the lining of the mouth appears to play a part. That is why no single trigger explains every person's sores, and why the answer to "why me?" is often a combination.

Common contributors to repeat canker sores

Small injuries inside the mouth

Biting your cheek, a sharp tooth edge, braces, a rough filling, an ill-fitting retainer or aggressive brushing can break the lining. For some people, a sore may develop where the tissue was irritated. If your sores appear in the same spot, ask your dentist to look for a rough surface.

Stress, sleep and hormonal shifts

Many people notice sores during stressful periods, poor sleep or around menstrual cycles. The link is reported often, though research has not shown it to be the same for everyone.

Foods and products that irritate

Some people connect outbreaks with acidic or sharp foods such as citrus, tomatoes, chips or nuts, or with certain toothpastes and mouthwashes. Some people find that toothpaste containing sodium lauryl sulfate bothers their mouth, though evidence is mixed. A short food and product diary can show whether you have a pattern.

Family tendency

Canker sores often run in families. If a parent or sibling gets them regularly, you may share a predisposition.

Nutrient shortfalls

Low iron, vitamin B12 or folate has been associated with recurrent mouth ulcers in some people. Diets low in these nutrients, absorption problems, heavy menstrual bleeding or some medications can contribute. Do not start high-dose supplements on your own; a clinician can check whether a deficiency is present and decide what is appropriate.

Medications

Some medicines, including certain anti-inflammatory pain relievers and some prescription drugs, have been linked to mouth ulcers in some people. If sores began after you started a new medicine, tell your prescriber or pharmacist. Do not stop or change a prescription on your own.

When repeat sores point to something beyond the mouth

Most people with recurrent canker sores are otherwise healthy. In a smaller group, sores are one sign of a condition that affects the body more widely. One sore pattern alone does not establish any of these, and they are much less common than everyday causes, but they are the reason a clinician asks about your whole health.

• Celiac disease. This immune reaction to gluten can cause mouth ulcers in some people, along with digestive symptoms, fatigue or anemia. See the NIH's MedlinePlus page on Celiac Disease for an overview. Do not cut gluten before you are tested, because that can make testing harder to interpret.
• Inflammatory bowel disease. Crohn disease and ulcerative colitis may come with mouth ulcers alongside belly pain, diarrhea, blood in the stool or weight loss.
• Behcet disease. This uncommon condition can cause frequent mouth sores along with genital sores, eye inflammation or skin lesions.
• Immune or blood conditions. Some conditions that affect immune function or blood counts can show up as persistent or severe mouth ulcers.
• Periodic fever syndromes. In some children, mouth sores recur with regular fevers and sore throat or swollen glands. A pediatrician can sort this out.

Is it really a canker sore? Look-alikes to know

Several mouth problems resemble canker sores but need different care.

• Cold sores. These are caused by the herpes simplex virus. They usually appear on or around the lips, often start with tingling, and are contagious. Canker sores form inside the mouth and are not contagious.
• Oral lichen planus. This inflammatory condition can cause white lacy patches, redness or painful erosions inside the cheeks. It is a different problem, and clinicians have reported on treating stubborn cases, for example in a case series on vitamin D in recalcitrant oral lichen planus. A case series is early evidence, not proof that a treatment works.
• Viral illnesses. Illnesses such as hand, foot and mouth disease can cause multiple small mouth sores, usually with fever and a rash on hands or feet.
• Allergic or drug reactions. Mouth sores that appear with a new medicine, especially along with a rash or blistering, need prompt attention.
• Oral cancer. This is much less common than benign causes, and a single sore does not suggest it. But a sore, white or red patch, or lump that does not heal or keeps growing should be examined, particularly if you use tobacco or drink heavily.

How clinicians evaluate recurrent mouth ulcers

Clinicians combine your history, an exam of the mouth and, when indicated, testing. Expect questions about how often sores come, how long they last, where they appear, how large they are, whether you get them with other symptoms, and which medicines and supplements you take.

If your pattern suggests it, your clinician may decide to check blood counts and levels of iron, vitamin B12 and folate, and may consider testing for celiac disease. Some people need a referral to a dentist, oral medicine specialist, gastroenterologist or rheumatologist. A biopsy can be considered for a sore that does not heal or looks unusual.

Before the visit, it helps to note when each sore started, how long it lasted, what you ate, your stress and sleep, your menstrual cycle if relevant, and any new products or medicines.

What may help at home

Canker sores often heal on their own without scarring, though how long that takes varies. Home care aims to reduce pain and avoid further irritation.

• Use a soft toothbrush and brush gently around the sore.
• Choose bland, cool or soft foods while the sore is active, and limit very acidic, salty, spicy or crunchy foods.
• Consider switching to a toothpaste without sodium lauryl sulfate if you suspect it bothers you.
• Rinsing with plain water or a mild salt-water rinse can feel soothing.
• Over-the-counter gels, pastes and rinses are available. Ask a pharmacist which are appropriate for you and read the label, as some are not meant for young children or for long-term use.

For children, follow the product label and ask a pediatrician or pharmacist before using any mouth product. Do not use adult products on a young child without that advice.

If sores are frequent or severe, your clinician may discuss prescription options such as topical corticosteroids or other medicines. These come with their own labeling and cautions, so use them only as prescribed and ask the prescriber about any concerns.

Reducing how often they return

• Keep a short diary of sore dates, foods, products, stress and sleep to look for repeating patterns.
• Have rough teeth, braces or dental appliances checked if sores appear in the same spot.
• Eat a varied diet and tell your clinician if you restrict food groups or have digestive symptoms, since that may affect nutrient levels.
• Tell your clinician about any new medicine that began before the sores did.

If you also wonder about other changes in your mouth, our articles on bad breath that persists despite brushing and flossing, a metallic taste in the mouth and chewing on ice cover related concerns and are linked below.

When mouth sores need prompt attention

Most canker sores are a nuisance, not an emergency. Call 911 if mouth sores come with trouble breathing, swelling of the lips, tongue or throat, or widespread blistering and peeling skin, which can be a severe reaction to a medicine or an infection. Also seek emergency care if pain keeps you from swallowing fluids and you feel faint or very weak from dehydration.

Arrange same-day or next-available care for sores that do not heal, large or deep sores, many sores at once, sores with fever, eye pain or redness, genital sores, ongoing diarrhea, belly pain or weight loss, or sores that make eating and drinking hard. The emergency box below lists these in more detail.

When to Seek Medical Care