Mouth Ulcers and Silent Allergies: Investigating the Food Link

Mouth Ulcers and ‘Silent Allergies’: Is Food Ever the Trigger?

Published: 28 February 2026 · Medically reviewed content · Written for UK patients

Mouth ulcers are one of the most common oral complaints in the UK — and one of the most frustrating. If you experience recurrent ulcers, you have almost certainly wondered whether something in your diet is to blame. The internet is full of lists linking certain foods to mouth sores, and it is natural to ask whether a hidden — or ‘silent’ — allergy could be behind them.

The reality is more nuanced. While food can sometimes play a role, the connection between mouth ulcers causes and true IgE-mediated food allergy is much less common than many people assume. Understanding which mechanisms are actually at work — irritation, intolerance, cross-reactive immune responses, or genuine allergy — can save time, avoid unnecessary dietary restriction, and point you towards the right type of investigation.

This guide explains the most common reasons for recurrent mouth ulcers, where food genuinely fits into the picture, when an IgE blood test may be helpful, and what practical steps you can take in the UK.

Seek urgent medical or dental advice if:

A mouth ulcer has lasted longer than three weeks without healing
An ulcer is unusually large, bleeding, or increasing in size
You have difficulty swallowing, breathing, or opening your mouth
You also have unexplained weight loss, persistent fatigue, or night sweats
You develop widespread swelling, a rash, or a high fever alongside mouth sores

A non-healing mouth ulcer can occasionally indicate a more serious condition and should always be assessed by a GP or dentist. If you experience breathing difficulty, throat swelling, or faintness after eating, call 999 — this may indicate anaphylaxis (NHS, 2025).

Start With the Basics: What Mouth Ulcers Are

Mouth ulcers — clinically known as aphthous ulcers or aphthous stomatitis — are small, round or oval sores that develop on the soft tissues inside the mouth: the inner cheeks, lips, tongue, gums, or the floor of the mouth. They are not the same as cold sores (herpes simplex), which typically appear on the outer lip and are caused by a virus (NHS, 2025).

Most aphthous ulcers are minor (less than 10 mm in diameter), heal within one to two weeks without scarring, and — while painful — are not dangerous. However, some people experience recurrent aphthous stomatitis (RAS), defined as repeated episodes occurring multiple times per year, sometimes with several ulcers present at once.

Recurrent mouth ulcers affect an estimated 20% of the UK population at some point (Allergy UK, 2025). The peak onset is typically between the ages of 10 and 40, and the condition tends to become less frequent with age. Despite being so common, the exact cause is often elusive — which is where the search for a food trigger usually begins.

Common Non-Allergy Causes (and Why This Matters for Negative Tests)

Before exploring the food-allergy angle, it is important to acknowledge that the majority of recurrent mouth ulcers are not caused by IgE-mediated food allergy. If you have had an allergy blood test that came back negative, this does not mean your ulcers are unexplained — it may simply mean the answer lies elsewhere.

Minor Trauma, Stress, Viral Illness, and Vitamin Deficiencies

The most commonly recognised triggers for aphthous ulcers include:

Mechanical trauma — biting the inside of the cheek, sharp edges on teeth or orthodontic appliances, vigorous toothbrushing, or ill-fitting dentures
Stress and fatigue — widely reported as a trigger or aggravating factor, though the mechanism is not fully understood. It may relate to stress-related immune changes (BSACI, 2024)
Viral illness — certain viral infections (particularly hand, foot, and mouth disease, and some herpesvirus infections) can cause mouth sores, though these often look clinically different from aphthous ulcers
Nutritional deficiencies — iron, vitamin B12, folate, and zinc deficiency have all been associated with recurrent aphthous ulceration. NICE guidance recommends screening for these when ulcers are persistent or recurrent (NICE, 2024)
Hormonal changes — some women report that mouth ulcers coincide with menstruation
Sodium lauryl sulphate (SLS) — a foaming agent found in many toothpastes. Some studies suggest that SLS-free toothpaste may reduce ulcer frequency in susceptible people (NHS, 2025)

These non-allergic causes are important to consider first, because they are far more common than food allergy as a driver of mouth ulcers — and because addressing them (e.g., correcting a vitamin deficiency or changing toothpaste) can resolve the problem without any dietary change.

Irritant Foods (Acidic/Spicy) vs Immune Allergy

Many people notice that certain foods seem to ‘cause’ mouth ulcers — or at least make existing ones worse. In most cases, this is an irritant effect rather than an immune response:

Acidic foods — citrus fruits, tomatoes, pineapple, and vinegar-based dressings can sting or aggravate an existing ulcer because the acid irritates exposed tissue. This is a chemical irritation, not an allergy.
Spicy foods — capsaicin and other compounds in chilli, curry, and hot sauces can trigger pain on contact with an ulcer, but do not cause the ulcer itself.
Hard or rough-textured foods — crisps, crusty bread, and toast can physically traumatise the oral mucosa and trigger new ulcers in susceptible people.

The distinction between irritant and immune-mediated responses is clinically important. An irritant reaction is localised, dose- dependent, and predictable — it happens because the tissue is already damaged, not because the immune system is mounting a response to a specific protein. It will not show up on an IgE blood test because IgE antibodies are not involved.

Where ‘Food’ Fits: Allergy, Intolerance, and Lookalikes

When people search for mouth sores allergy or intolerance, they are often trying to distinguish between several different mechanisms. Here is a plain-language overview of each.

IgE Food Allergy — What Symptoms Usually Look Like

A true IgE-mediated food allergy occurs when the immune system produces IgE antibodies against a specific food protein. On subsequent exposure, these antibodies trigger mast cell activation and histamine release, producing symptoms that are typically:

Rapid in onset — usually within minutes, and almost always within two hours of eating the food
Multi-system — commonly involving skin (hives, flushing, swelling), gut (nausea, vomiting, abdominal pain), airways (wheeze, throat tightness), and/or cardiovascular symptoms (dizziness, faintness)
Reproducible — the same food triggers the same type of reaction each time

Isolated, recurrent aphthous mouth ulcers — without any of the above accompanying symptoms — are not a typical presentation of IgE food allergy. This is why many people who request food allergy testing specifically for mouth ulcers receive negative results. The test is working correctly; the ulcers are simply being driven by a different mechanism (Allergy UK, 2025).

Pollen Food Syndrome (Oral Allergy Syndrome): Mouth Symptoms After Raw Fruit and Vegetables

This is the food-related immune condition most likely to produce oral allergy syndrome mouth symptoms. Pollen food syndrome (PFS) occurs in people who are already sensitised to certain pollens — most commonly birch pollen in the UK. Their IgE antibodies, originally directed against pollen proteins, cross- react with structurally similar proteins in certain raw fruits, vegetables, and nuts (Allergy UK, 2025).

The typical symptoms of PFS are:

Itching, tingling, or mild swelling of the lips, mouth, tongue, or throat
Symptoms appearing within minutes of eating raw food (cooking usually breaks down the cross-reactive proteins)
Symptoms resolving on their own within 30–60 minutes
No systemic symptoms (no hives elsewhere, no breathing difficulty, no gut involvement)

PFS symptoms are distinct from aphthous ulcers: they are immediate, short-lived, and primarily involve itching and tingling rather than the formation of a discrete, slow-healing sore. However, the overlap in location — both affect the mouth — is why people sometimes conflate the two. If your symptoms are itching or tingling within minutes of eating raw apple, cherry, hazelnut, or kiwi (especially if you also have hay fever), pollen food syndrome is a more likely explanation than aphthous ulcers (BSACI, 2024).

Contact Reactions and Irritant Effects

Some oral reactions to food are best described as contact irritation — a direct chemical effect on the mucosal surface that does not involve IgE antibodies. Common examples include:

Cinnamic aldehyde (in cinnamon) — can cause a burning sensation and, in some people, contact stomatitis
Benzoic acid and sorbic acid — preservatives found in processed foods that may irritate the oral mucosa
Nickel — present in certain foods (chocolate, oats, legumes) and implicated in some cases of recurrent oral mucosal reactions, particularly in people with known nickel contact allergy (which is a type IV, T-cell-mediated response, not IgE-mediated)

These contact reactions are not detected by IgE blood testing because they involve different immune pathways (type IV) or are purely chemical irritant effects. If your GP or dermatologist suspects a contact allergy, patch testing — not IgE blood testing — is the appropriate investigation (NHS, 2025).

Other Conditions That Can Look Like Food-Triggered Ulcers

Certain systemic conditions can cause oral ulceration that might initially be attributed to food. These include:

Coeliac disease — an autoimmune condition triggered by gluten, in which recurrent mouth ulcers are a recognised feature. This is not the same as an IgE wheat allergy (NICE, 2024).
Inflammatory bowel disease (Crohn's disease, ulcerative colitis) — oral ulcers can be an extra-intestinal manifestation
Behçet's disease — a rare inflammatory condition causing recurrent oral (and genital) ulceration
Drug reactions — certain medications (including NSAIDs, beta-blockers, and some chemotherapy agents) can cause mouth ulcers as a side effect

If your mouth ulcers are frequent, severe, or accompanied by other symptoms (joint pain, gut problems, skin rashes, genital ulcers, or unexplained weight loss), these conditions should be explored by your GP before pursuing food allergy testing.

A Practical Way to Investigate a Food Link Safely

If you have ruled out the most common non-food causes with your GP or dentist and still suspect that something in your diet is contributing to your ulcers, a structured approach is more productive — and safer — than cutting out foods randomly.

Symptom and Food Diary: What to Track

A food diary for mouth ulcers is one of the most useful first steps, because it can reveal patterns that are not obvious from memory alone. Here is what to record:

Date and time of each ulcer appearing
Location, size, and severity — inside of cheek, tongue, gum, etc.
All foods and drinks consumed in the 24–48 hours before onset (not just suspected triggers)
Any new products — toothpaste, mouthwash, chewing gum
Stress levels, sleep quality, illness — context that might explain ulcer onset
Menstrual cycle (if applicable)
Time to healing — how long each episode lasts

Aim to keep the diary for at least four to six weeks. The goal is to spot consistent patterns: does the same food precede ulcers repeatedly? Or does the timing better correlate with stress, hormonal changes, or a new toothpaste? A diary makes these connections visible and provides your GP with concrete information to work from (Allergy UK, 2025).

Red Flags for Urgent Care

While you are investigating, remain aware of situations that warrant prompt medical attention:

Any ulcer lasting more than three weeks (NHS referral guidance recommends urgent assessment to exclude serious pathology)
Ulcers accompanied by difficulty swallowing, unexplained weight loss, or persistent swollen lymph nodes
Immediate-onset symptoms after eating (swelling, hives, breathing difficulty) — which suggest a possible IgE-mediated allergic reaction and may require emergency care
Rapidly worsening oral pain with fever — which may indicate infection rather than simple aphthous ulceration

When IgE Blood Testing Is Relevant vs Not

An IgE blood test measures whether your immune system has produced IgE antibodies against a specific allergen. It is most useful when:

Your diary suggests a pattern of immediate-onset oral symptoms (itching, tingling, swelling) after eating a specific food — which may indicate pollen food syndrome or IgE food allergy
You have other symptoms of atopic disease (eczema, asthma, hay fever) alongside your oral symptoms
You suspect a connection between your oral symptoms and a specific group of raw fruits or vegetables

IgE blood testing is less likely to be informative when:

Your ulcers develop slowly (over hours or days) without any immediate-onset symptoms
Your ulcers are the only symptom — with no hives, swelling, gut symptoms, or respiratory involvement
You suspect an irritant or contact reaction (e.g., to acidic foods, spices, or toothpaste ingredients) — these do not involve IgE antibodies
You suspect coeliac disease — which requires different testing (tTG antibodies, not IgE food panels)

Understanding this distinction before booking a test can help you avoid disappointment and ensure you choose the investigation most likely to provide useful answers.

How Nurse-Led Allergy Blood Tests Can Help (and Their Limits)

If your clinical history and diary suggest that an IgE-mediated food reaction may be contributing to your oral symptoms, a specific IgE blood test can provide valuable diagnostic information. Here is how the process works and what you can realistically expect.

Selecting Targeted Allergens Based on Your Diary

The most useful allergy blood test is a targeted one — where the allergens tested reflect your actual symptom history. Broad-spectrum panels that screen for dozens of foods you have never reacted to can generate confusing results (including clinically irrelevant positive results due to cross-reactivity) and may lead to unnecessary dietary restriction.

Before booking a test, consider:

Which specific foods consistently appear in your diary before symptoms?
Are the symptoms immediate (minutes) or delayed (hours/days)? IgE testing is designed for immediate-type reactions.
Do you have hay fever? If so, raw fruit/vegetable symptoms may reflect pollen food syndrome — and pollen-specific IgE testing may be more informative than testing the food itself.

Allergy Clinic offers nurse-led venepuncture (blood draw) with your sample sent to an accredited laboratory for specific IgE analysis. This is a diagnostic sampling service — it does not include a doctor consultation, clinical diagnosis, or treatment plan. Once you receive your laboratory report, you can share it with your GP or specialist for clinical interpretation and next steps. Explore the available panels on our allergy tests page.

What Testing Can and Cannot Tell You

A positive IgE result = sensitisation. Your immune system has produced IgE antibodies against that food. This does not automatically confirm that the food is causing your mouth ulcers.
IgE levels do not predict severity. A higher kU/L value does not mean a more severe reaction will occur.
Negative results are informative too. A negative result makes IgE-mediated allergy to that food much less likely, which can provide reassurance and prevent unnecessary avoidance.
Cross-reactivity can cause unexpected positives. If you are sensitised to birch pollen, your test may show positive results for apple, hazelnut, or cherry — even if you eat them without problems. This is cross-reactivity, not necessarily clinical allergy.
Results require clinical interpretation. Your report should always be reviewed alongside your symptom diary and clinical history by a qualified clinician.

Frequently Asked Questions

Can a food allergy cause mouth ulcers on its own?

It is uncommon for a classic IgE-mediated food allergy to present solely as mouth ulcers. IgE food allergies typically produce rapid-onset, multi-system symptoms — hives, swelling, vomiting, or breathing difficulty — not the slow-developing, round sores that define aphthous ulcers. However, pollen food syndrome can cause mouth-area itching and tingling after eating certain raw fruits and vegetables. If your only symptom is recurrent mouth ulcers without other allergic features, non-allergic causes are statistically more likely and should be explored with your GP or dentist first (NHS, 2025).

Is oral allergy syndrome the same as an anaphylaxis risk?

Not usually. Oral allergy syndrome (pollen food syndrome) causes mild, short-lived symptoms confined to the mouth and throat — itching, tingling, and minor swelling — after eating certain raw fruits, vegetables, or nuts. Anaphylaxis is a severe, life-threatening systemic reaction affecting breathing and/or circulation. PFS very rarely progresses to anaphylaxis. However, any episode involving breathing difficulty, widespread swelling, or faintness should be treated as a medical emergency. If in doubt, call 999 (Anaphylaxis UK, 2025).

Why do tomatoes sometimes sting existing mouth ulcers?

Tomatoes are naturally acidic (pH around 4.0–4.5). When acidic foods contact an existing ulcer — where the protective mucosal surface is already broken — they cause a sharp stinging or burning sensation. This is an irritant reaction, not an allergic one. Other common irritants include citrus fruits, vinegar, and spicy foods. The stinging does not mean you are allergic to tomatoes, but it may help to avoid highly acidic foods while an ulcer is healing (NHS, 2025).

Should I cut out multiple foods at once to find my trigger?

Eliminating several foods simultaneously is generally not recommended without professional guidance. It can lead to nutritional gaps, make it harder to identify the actual trigger, and may result in an unnecessarily restricted diet. A more effective approach is to keep a structured food diary for mouth ulcers, then discuss your findings with your GP or a registered dietitian. If a single food is suspected based on a clear pattern, a guided elimination of that food — with planned reintroduction — is safer and more informative than broad restriction (Allergy UK, 2025).

When should I seek medical or dental assessment for a mouth ulcer?

The NHS recommends seeking professional advice if a mouth ulcer has lasted longer than three weeks, if it keeps coming back, if it is unusually large or painful, if you also have unexplained weight loss or fatigue, or if the ulcer bleeds or is increasing in size. A non-healing mouth ulcer can occasionally indicate a more serious condition, including oral cancer, so persistent ulcers should always be assessed by a GP or dentist (NHS, 2025).

Can a blood test tell me if my mouth ulcers are caused by a food allergy?

A specific IgE blood test can tell you whether you are sensitised to a particular food — meaning your immune system has produced IgE antibodies against it. However, sensitisation does not automatically confirm that the food is causing your ulcers. Recurrent aphthous ulcers are only rarely caused by IgE-mediated food allergy. IgE testing is most useful when your history suggests immediate-onset symptoms (mouth itching, swelling, hives) after eating a specific food. Results should always be interpreted alongside your symptom diary by a qualified clinician (BSACI, 2024).

Are mouth ulcers a sign of coeliac disease?

Recurrent mouth ulcers can be a feature of coeliac disease, an autoimmune condition triggered by gluten. NICE guidelines list oral ulceration as a possible presentation of coeliac disease in adults. If you have persistent mouth ulcers alongside bloating, diarrhoea, fatigue, or unexplained iron deficiency, your GP may consider coeliac screening (typically a tissue transglutaminase antibody test). Coeliac disease is not the same as an IgE-mediated wheat allergy — they are distinct conditions requiring different investigations (NICE, 2024).

Bringing It Together

Recurrent mouth ulcers are common, frustrating, and often multi-factorial. While food is a natural suspect, the connection between mouth ulcers causes and true IgE food allergy is less straightforward than many people hope. The most productive approach is:

Rule out the common culprits first — trauma, stress, nutritional deficiencies, toothpaste ingredients, and underlying conditions like coeliac disease
Keep a structured food and symptom diary to identify genuine patterns
Distinguish irritation from allergy — acidic foods stinging an existing ulcer is not the same as an immune response
Consider IgE testing if your diary suggests immediate-onset oral symptoms after specific foods, especially if you also have hay fever or other atopic conditions
Share your results with a clinician who can interpret them in the context of your full history

Thinking About Getting Tested?

If your symptom diary suggests that an IgE-mediated food reaction may be contributing to your oral symptoms, Allergy Clinic offers private allergy testing with nurse-led venepuncture. Your sample is sent to an accredited laboratory and your report is returned to you directly — ready to share with your GP or specialist for clinical interpretation and next steps.

Explore Allergy Test Panels

Sources

NHS — Mouth ulcers, Food allergy, Anaphylaxis, Cold sores (2025)
Allergy UK — Food allergy factsheets, Oral allergy syndrome (pollen food syndrome) guidance (2025)
Anaphylaxis UK — Anaphylaxis action plans, Food allergy resources (2025)
BSACI — Guidelines on food allergy diagnosis and management (2024)
NICE — Coeliac disease: recognition, assessment and management (NG20, updated 2024); Aphthous ulcer (CKS, 2024)
Food Standards Agency — UK allergen labelling guidance (2025)
Moorfields Eye Hospital NHS Foundation Trust — referenced for general NHS clinical standards

Quick Glossary

IgE (Immunoglobulin E) — a type of antibody involved in allergic responses. Elevated specific IgE to a substance indicates sensitisation.
kU/L — kilo units per litre, the standard unit for reporting specific IgE levels in allergy blood test results.
Sensitisation — the presence of IgE antibodies showing the immune system has responded to a substance. Not the same as confirmed clinical allergy.
Cross-reactivity — when IgE antibodies raised against one protein also recognise structurally similar proteins from a different source (e.g., birch pollen and apple).
Aphthous ulcer — the medical term for a common mouth ulcer; a small, round or oval sore on the soft tissues of the mouth.
Pollen food syndrome (PFS) — an IgE-mediated cross-reactive condition in which pollen-sensitised people experience mild oral symptoms when eating certain raw fruits, vegetables, or nuts. Also called oral allergy syndrome.
Coeliac disease — an autoimmune condition triggered by gluten. Not the same as IgE-mediated wheat allergy.

Disclaimer: This article is for general information only and does not constitute medical advice, diagnosis, or treatment. The content is based on publicly available UK health guidance and published literature at the time of writing. Allergy Clinic provides nurse-led venepuncture and laboratory-processed specific IgE blood testing. It does not provide doctor consultations, clinical diagnosis, or prescribing. Always consult a qualified healthcare professional for interpretation of test results and personalised medical guidance.