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Mouth ulcer

Written by Healthwords's team of doctors and pharmacists based in UK | Updated: 26.01.2023 | 2 min read

A mouth ulcer occurs when a part of the lining of the inside of your mouth becomes damaged. The area that hurts is known as a mouth ulcer. They are very common and can be caused by many different things. The majority are not caused by anything serious and will improve on their own within 2 weeks. They look like red and white lesions on the inside of your cheeks that are usually 1cm in size or less. You can sometimes get large mouth ulcers which are bigger than this and they can also appear at the bottom of the gums, under or on the tongue.

What causes them?

The most common cause is an injury to the inside of the mouth which can be through accidentally biting it, dentures or braces rubbing on the mouth, eating or drinking food that is too hot or too acidic, and any injury with a rough or sharp object. Other causes can be due to stress, vitamin deficiencies, pregnancy, some medication, inflammatory conditions, and in very rare cases mouth cancer (ulcers due to this don’t heal and are more likely to be around the tongue area.) You are also more likely to develop mouth ulcers if your family members suffer from mouth ulcers, you have a lowered immune system or you have just stopped smoking. Mouth ulcers are not contagious.

Caidr pharmacists' top tips

There are things you can do to help with your mouth ulcer. These include avoiding using stiff toothbrushes, abrasive mouthwashes, hard or sharp food such as crisps, and acidic or spicy foods. You can also get over-the-counter medicines that can help relieve pain and can sometimes shorten the healing time. Examples of these are lozenges, gel, sprays and antimicrobial mouth wash. You can speak with your local pharmacist if you are unsure which is right for you.

When should I see my doctor?

You should see your doctor if it is not improving after two weeks if it is a large ulcer, if you are having recurring ulcers or if you think the ulcer may be infected (increasing redness, bleeding or you are feeling generally unwell with a fever). You should also see your doctor if you are having any other symptoms along with mouth ulcers such as fatigue and stomach pain.

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