How Coffee Could Give You Mouth Ulcers: From Heart Pills to Blueberries, the Surprising Causes of those Painful Sores

Ulcers are often the sign of physical trauma (hard toothbrushing or ill‑fitting dentures, for instance). While they can make it painful to eat or talk normally, they usually clear up on their own within days.

But one in five of us suffers from recurrent bouts of mouth ulcers, which often have no obvious cause.

Persistent ulcers can be a sign that “something in the body is not working as well as it should”, explains Stephen Porter, professor of oral medicine at the University College London Eastman Dental Institute.

Conditions such as Crohn’s disease, iron deficiency anaemia and vitamin B12 deficiency can all lead to lingering ulcers that won’t easily heal. “The key is not what each ulcer looks like, but how long it takes to heal. Any that hang around longer than three weeks need referral for investigations, as there could be an underlying medical issue,” adds Professor Porter.

Here, we look at what could be causing your mouth ulcers and what you can do about them.


It could be stress – or your period

The most common form of ulcer is called an aphthous ulcer. These look like a typical ulcer: round or oval sores, and are usually under 10mm in diameter.

What sets aphthous ulcers apart from more ordinary ulcers is that they usually take two or three weeks to clear without treatment, and the person affected is otherwise generally well. Typically, there is no obvious cause, although one theory is that they are linked to stress.

Some people do report that these crop up when they are under pressure, and some women develop them during their period, but this is unproven, says Professor Porter.

“It may just be that these people are hypersensitive to pain when their body is under stress, so they notice mouth ulcers that might at other times not trouble them. Another theory, though unproven, is that stress suppresses the immune system which, in turn, changes the lining of the mouth,” he says.

The pain from ulcers is caused by their proximity to underlying nerves.


Sensitivity to chocolates and coffee

Eating blueberries, strawberries, blackberries or even chocolate can trigger a mouth ulcer in some people. The reason is sensitivity to theobromine, an alkaloid found in chocolate; or to salicylic acid, found in blueberries, blackberries and strawberries. These substances are also found in coffee, almonds, cheese and tomatoes.

“A few people report developing mouth ulcers after eating these foods – but it’s not technically an allergy and is not accompanied by other allergic symptoms, such as hives,” says Maureen Jenkins, a clinical adviser with the charity Allergy UK. Such ulcers disappear within a week.

Lack of iron or vitamin B12

If you regularly develop ulcers and feel tired all the time, it might be worth reviewing your diet.

Deficiencies in vitamin B12 and iron can both lead to mouth ulcers, because the cells of the lining of the mouth need these nutrients to regenerate efficiently.

“These ulcers may look the same as aphthous ulcers, but they would be accompanied by symptoms of feeling unwell, such as tiredness and breathlessness,” says Professor Porter.

Iron deficiency anaemia, a condition where a lack of iron leads to a reduction in the number of red blood cells, is common in women of childbearing age if they experience heavy periods and during pregnancy.

The most common cause of B12 deficiency is pernicious anaemia, an autoimmune condition. This causes the body to attack cells in the stomach, which produce a protein called intrinsic factor, which aids B12 absorption. Older people are especially at risk of this.

For some, it may simply be that their diet is lacking in these nutrients – B12 is commonly found in meat, milk and eggs, while iron is in red meat and green leafy veggies such as kale, as well as brown rice.

“When an iron or B12 deficiency is at play, the cause must be identified and rectified, although patients may also need iron supplements or B12 injections,” says Professor Porter. “Once iron or vitamin B12 levels return to normal, the mouth ulcers will go away.”

These ulcers may look the same as aphthous ulcers, but they would be accompanied by symptoms of feeling unwell.


Too firm a toothbrush

Dentures, orthodontic braces, ill-fitting dental plates, and even the sharp edges of your own teeth can all cause ulcers if they cut the lining of the mouth, explains Dr. Uchenna Okoye, a dentist from the London Smiling clinic.

It’s usually obvious what is causing the problem, so see your dentist and ask for adjustments to be made to the offending brace or dentures. Dentists can also smooth down a sharp tooth.

Just using a firm toothbrush can also damage the lining of the mouth, and that can lead to an ulcer. Switching to a soft-bristle toothbrush may also help if you frequently cause bristle damage.


Gut disease

Recurrent mouth ulcers – especially those accompanied by tiredness and weight loss – may be a sign of coeliac disease. This autoimmune condition causes an adverse reaction to gluten, a protein found in wheat, barley and rye.

“The antibodies released by the immune system in response to gluten damage the lining of the gut, so nutrients such as iron and folate are not absorbed properly,” explains Professor Chris Hawkey, a gastroenterologist and chairman of gut and liver charity CORE. “These are needed for cell repair, including in the mouth.”

A blood test or biopsy of the gut is used to diagnose coeliac disease. Ulcers with a “cobblestone” appearance or that form in straight lines and are deeper than a standard ulcer could be a sign of Crohn’s disease.

Caused by inflammation in the lining of the gut from the mouth to the anus, Crohn’s gives rise to symptoms such as diarrhoea, abdominal pain and weight loss, and can also trigger larger ulcers.

“Mouth ulcers caused by Crohn’s tend to be more like swollen raised lumps,” says Professor Hawkey.

These sometimes, though not usually, occur before gut symptoms.


Smoking cessation

Giving up cigarettes brings major health benefits, but some people develop ulcers in the days or weeks after they give up. “One theory is that smoking hardens the lining of the mouth, which increases its resistance to physical damage,” says Professor Porter. “When you give up, this resistance goes down, so you are more likely to develop them. They are basically aphthous ulcers – it is just that smoking has previously masked them.”



Everyday non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen, or beta-blockers such as propranolol (to treat heart disease and high blood pressure), can increase the risk of a mouth ulcer.

Immunosuppressant drugs including methotrexate (for rheumatoid arthritis) and drugs that can cause a dry mouth, such as the antidepressant amitriptyline, can also raise the risk, as can the angina drug nicorandil.

“Ulcers caused by nicorandil are usually quite large and more dramatic than ordinary mouth ulcers and can occur anywhere from the mouth to the anus,” says Professor Hawkey. These drugs may interfere with the body’s immune defence mechanisms, allowing them to attack the lining of the mouth.

“Chemotherapy and radiotherapy can also cause temporary mouth ulcers because they slow down cell division throughout the body, and the cells in the lining of the mouth don’t repair quickly enough,” says Professor Hawkey.


Oral cancer

In rare cases, what looks like a mouth ulcer can actually be a sign of oral cancer, which affects 6,000 people a year. “These are almost always single ulcers that have no obvious physical causes, such as trauma, and do not get better with over-the-counter mouthwash or gel,” says Professor Porter.

“It might not even feel painful. The key thing is that it doesn’t heal within three weeks. Most oral cancers are diagnosed too late because patients think they have a harmless mouth ulcer.”

Other symptoms include white or red patches on the inside of the mouth, difficulty swallowing, speech problems, a lump in the neck and weight loss.


What to do to beat the pain

Avoid hard and acidic foods. For people prone to ulcers, hard foods (including toast and crisps) may cut or rub against the ulcer, while acidic foods (such as citrus fruits and vinegar) can make ulcers sting.

Use a gel before bed.

  • Over-the-counter gels such as Bonjela – which contains choline salicylates, a type of NSAID – reduce pain (there are specially formulated versions for children).

    Yvonne Lee, a dental adviser with the British Dental Health Foundation helpline, says: “Apply gels an hour and a half before you eat to get the numbing effects when you need it, or when you go to bed so the gel is undisturbed in your mouth.” Other treatments for adults include topical painkillers such as benzydamine hydrochloride, a mouthwash or spray with painkilling properties.

  • Another option is anti-microbial mouthwashes such as chlorohexidine to kill the bacteria that might make your mouth ulcer worse.

  • Sprays or gels containing local anaesthetics such as lidocaine can numb the pain.

Take a steroid. Low-strength topical corticosteroids (such as hydrocortisone buccal tablets, which dissolve in the mouth next to the ulcer) can reduce the duration and severity of mouth ulcers, but won’t stop new ones from forming. – Jo Waters, The Daily Mail