Why Do I Keep Getting Mouth Ulcers?
The honest verdict
This is usually not an allergy
Mouth ulcers are rarely caused by allergies. The vast majority are canker sores (aphthous ulcers) — small, painful, round or oval sores with a white or yellow center and a red border. They are triggered by stress, minor injury (biting your cheek), acidic or spicy foods, hormonal changes, or immune sensitivity. Cold sores (fever blisters) are caused by the herpes simplex virus and appear on the lips or around the mouth. True allergic causes — such as oral allergy syndrome from raw fruits or contact stomatitis from dental products or metals — are possible but uncommon. Ulcers that persist beyond 3 weeks, recur frequently, or occur with fever or weight loss should be evaluated by a clinician.
This is a general research summary, not a diagnosis. It can't tell you what's causing your symptom — a clinician can.
Check this first
When mouth ulcers is an emergency
Most of the time this can be handled calmly. But a few signs mean you shouldn't wait. Match what you're seeing to the right level of care below.
If any emergency sign below is present, call 911 or go to the ER now.
- Emergency
Difficulty swallowing, drooling, or trouble breathing with mouth sores — go to the ER (possible severe infection or angioedema).
Call 911 or go to the ER now
- Urgent
Sores that spread rapidly, are unusually large or deep, or are accompanied by blisters on the skin — seek urgent care (possible viral infection like herpes or hand-foot-mouth disease).
Get seen today — urgent care or same-day visit
- See a doctor
Ulcer that does not heal after 3 weeks — see a dentist or doctor (possible oral cancer or other serious condition).
Book a routine visit with a clinician
- See a doctor
Ulcer with a red, white, or dark patch on the cheek, gum, or tongue that does not go away — seek evaluation (possible oral cancer screening needed).
Book a routine visit with a clinician
- See a doctor
Mouth sores accompanied by fever, rash, joint pain, or eye inflammation — see a clinician (possible autoimmune or systemic disease).
Book a routine visit with a clinician
When in doubt, err toward getting seen. These tiers are a general guide, not a substitute for a clinician's judgment about your specific situation.
Key facts
Canker sores (aphthous ulcers) affect about 20% of the population at any given time, making them the most common type of mouth ulcer.
Oral allergy syndrome (pollen-food allergy syndrome) affects up to 60% of people with hay fever, but it causes itching and tingling — not painful ulcers.
Mouth ulcers that do not heal within 3 weeks should be evaluated for oral cancer — about 54,000 new cases of oral cancer are diagnosed in the U.S. each year.
National Institutes of Health (NIH) — National Cancer Institute
What's causing it
The same symptom can come from very different places. Here are the usual suspects for Mouth — including the inside of the cheeks, lips, tongue, gums, soft palate, and throat, tagged by mechanism and how common each one is — so you can see where an allergy actually fits.
Canker sores (aphthous ulcers)
Small, painful, round or oval ulcers with a white or yellow center and red border. They appear inside the mouth — on the cheeks, lips, tongue, or soft palate — and are not contagious. Triggers include stress, minor injury (biting the cheek), acidic or spicy foods, hormonal shifts, and immune sensitivity. Most heal in 7–14 days without scarring.
Cold sores (herpes simplex virus, HSV-1)
Blister-like sores that typically appear on the lips or around the mouth, sometimes on the gums or hard palate. They are contagious and often preceded by tingling or burning. Triggered by stress, illness, sun exposure, or immune suppression. Antiviral medications can reduce duration and severity.
Trauma or injury
Accidentally biting the inside of the cheek or lip, burns from hot food or drinks, irritation from braces, sharp teeth, or ill-fitting dentures can cause a single, painful ulcer. These typically heal within a week once the source of irritation is removed.
Nutritional deficiencies
Deficiencies in vitamin B12, folate, iron, or zinc are linked to recurrent aphthous ulcers. A blood test can identify deficiencies; correcting them with diet or supplements may reduce ulcer frequency. This is more common in people with digestive conditions that affect nutrient absorption.
Oral allergy syndrome (pollen-food allergy syndrome)
A mild allergic reaction to raw fruits, vegetables, or nuts in people with pollen allergies (hay fever). It causes itching, tingling, or mild swelling of the lips, tongue, or throat — not typically painful ulcers. Symptoms resolve quickly when the food is swallowed or removed. Cooking the food usually eliminates the reaction.
Autoimmune conditions
Recurrent, painful mouth ulcers can be a feature of autoimmune diseases such as Behçet's disease, lupus, inflammatory bowel disease (Crohn's disease, ulcerative colitis), or celiac disease. These ulcers are often larger, deeper, and accompanied by systemic symptoms like joint pain, fatigue, or gastrointestinal issues.
Is this an allergy? Usually, no
It's a common assumption, so it's worth being clear about — and pointing you toward what's more likely going on.
Mouth ulcers are usually not an allergy. The most common type — canker sores — are not allergic in nature. A true allergic cause, such as oral allergy syndrome (pollen-food allergy syndrome), causes itching, tingling, or mild swelling of the lips and mouth after eating raw fruits or vegetables, but it rarely produces painful ulcers. Contact stomatitis from dental products, metals, or certain foods can cause mouth soreness or ulceration in some people, but this is uncommon. If mouth ulcers occur with hives, lip or tongue swelling, or trouble breathing after eating, an allergic reaction is possible and should be evaluated by an allergist.
Because an allergy is unlikely to be the driver, the most useful next step is a clinician who can look at the actual cause — not an allergy test.
Relief you can try at home
If your symptom is mild and you have no red-flag signs, these gentle steps often help. They soothe — they don't replace figuring out the cause.
- 1
Rinse with salt water or baking soda
Mix 1/2 teaspoon of salt or baking soda in a cup of warm water. Swish gently for 30 seconds and spit. This can soothe pain and help keep the area clean. Repeat 2–3 times daily.
- 2
Use over-the-counter topical products
Products containing benzocaine, hydrogen peroxide, or a protective paste (like Orabase) can numb the area and form a barrier over the ulcer. Follow label directions and avoid overuse.
- 3
Avoid irritating foods
Spicy, salty, acidic (citrus, tomatoes), or crunchy foods can aggravate mouth ulcers. Stick to soft, bland foods (yogurt, oatmeal, mashed potatoes) and cool or lukewarm drinks until the ulcer heals.
- 4
Apply a cold compress or ice
Sucking on an ice cube or applying a cold compress to the outside of the cheek near the ulcer can reduce pain and inflammation. This is especially helpful for cold sores on the lips.
- 5
Manage stress and triggers
If you get recurrent canker sores, keeping a diary of triggers (stress, foods, sleep, hormonal cycles) can help identify patterns. Stress reduction techniques, adequate sleep, and a balanced diet may reduce frequency.
Stop any step that makes things worse. If the symptom isn't easing within a few days, check in with a clinician.
When to see a doctor
See a dentist or doctor if a mouth ulcer does not heal after 3 weeks, is unusually large or deep, or is accompanied by a red, white, or dark patch in the mouth. Seek medical attention for mouth sores with fever, rash, joint pain, weight loss, or eye inflammation. Difficulty swallowing, drooling, or trouble breathing with mouth sores requires emergency care. If you have frequent, painful ulcers that interfere with eating or drinking, a clinician can evaluate for underlying causes such as nutritional deficiencies, autoimmune conditions, or viral infections.
❓Frequently Asked Questions
Mouth ulcers are rarely a sign of an allergy. Most are canker sores triggered by stress, injury, or immune sensitivity. Oral allergy syndrome causes itching and tingling, not painful ulcers. Contact allergies to dental products or metals can cause mouth soreness but are uncommon. If mouth ulcers occur with hives, swelling, or trouble breathing after eating, an allergic reaction is possible.
Canker sores are small, painful ulcers inside the mouth (cheeks, lips, tongue) with a white or yellow center and red border. They are not contagious. Cold sores are blister-like sores caused by the herpes simplex virus, usually on the lips or around the mouth, and they are contagious. Cold sores often tingle or burn before appearing.
Most canker sores heal on their own within 7–14 days without scarring. Cold sores typically heal in 7–10 days. Ulcers that last longer than 3 weeks should be evaluated by a dentist or doctor to rule out more serious conditions like oral cancer or autoimmune disease.
Yes — stress is a well-known trigger for canker sores. Emotional stress, lack of sleep, and physical stress (illness, injury) can weaken the immune system and increase the likelihood of developing aphthous ulcers. Managing stress through relaxation techniques, adequate sleep, and a healthy diet may help reduce recurrence.
Deficiencies in vitamin B12, folate (B9), iron, and zinc are associated with recurrent aphthous ulcers. A simple blood test can identify these deficiencies. Correcting them through diet (leafy greens, lean meats, fortified cereals) or supplements may reduce the frequency and severity of outbreaks.
Medically reviewed by
Dr. Chet TharpeMD
Last reviewed July 2026
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Read moreThe best next step is a real clinician
This symptom is usually not driven by an allergy, so an allergy test won't give you the answer. A primary care doctor or the right specialist can examine what's actually going on and guide you from there.
Curex focuses on at-home allergy testing and immunotherapy, which isn't the right fit for this symptom — and never a substitute for medical care.
- 1Mayo Clinic — Canker Sore: Symptoms and Causes
- 2Cleveland Clinic — Mouth Ulcers: Types, Causes & Treatment
- 3American Academy of Allergy, Asthma & Immunology — Oral Allergy Syndrome
- 4MedlinePlus — Mouth Ulcers (National Library of Medicine)
- 5American Academy of Oral Medicine — Aphthous Ulcers (Canker Sores)
This content is for informational purposes only and does not constitute medical advice, diagnosis, or treatment. It cannot tell you what is causing your mouth ulcers or whether it is an allergy. If you have any emergency sign — trouble breathing, fast-spreading swelling, sudden weakness or confusion, or severe pain — call 911 or go to the nearest emergency room. For anything that is new, worsening, or persistent, see a licensed healthcare provider. Curex focuses on at-home allergy testing and immunotherapy, which is not the appropriate care for this symptom and never a substitute for a clinician.