If you’ve ever bitten the inside of your lip or gum by accident while eating, you have likely had a mouth ulcer. That’s right – the bogeyman that endless creams and gels advertised on TV promise to fight is relatively common.

However, while most forms of mouth ulcers are relatively benign, it is crucial to be aware of the risks, particularly if you have a recurring ulcer or one that doesn’t heal.

Mouth ulcers can have many causes, and it is essential to check your mouth for them. So, what are mouth ulcers, what causes them, and what should you do if you have one?

What Are they?

Also known as canker sores, ulcers are small, painful lesions that can arise at the base of your gums or in your mouth. These lesions are the loss or erosion of tissue that lines your mouth.

Usually red or yellow, these sores are generally benign. However, if an ulcer lasts longer than two or three weeks, or keeps coming back, it can indicate something more sinister.

A particularly painful and red sore can suggest an infection, and an ulcer that lasts for a long time can be a sign of mouth cancer. In both instances, it is best to go to your dentist for a check-up.

There are three main types of ulcers:


The minor type is the most common, and it can appear inside the cheeks and on the lips, gums, and tongue. Sometimes coming in a cluster of four or six, these sores can be as small as 2 mm and as large as 8 mm across. Minor sores tend to clear up within two weeks.


Not just bigger than minor ulcers, major sores are more severe and can take up to six weeks to clear up, often leaving scar tissue once they have disappeared. They penetrate further into the tissue inside your mouth and have irregular edges.

Major ulcers may also occur near your tonsils and can be very painful. If you have had a large ulcer for more than three weeks, you should see a dentist.

Herpetiform ulceration (HU)

Herpetiform ulcers are tiny and occur in clusters of between ten and 100. While the name stems from the ulcer’s resemblance to herpes sores, HU is not contagious. However, they do recur very quickly, which makes it seem like there is a continuous infection.

These lesions can grow to form one larger, ragged sore. This type of ulcer tends to heal without scarring and within two weeks.


Mouth ulcers can flare for a range of reasons. Often, ulcers are incidental – they can result from biting your lip or gum by accident while you are eating, an accident while cleaning your teeth, or a burn from eating hot food. In other scenarios, it can be more severe and require a visit to the dentist.

Other causes of mouth ulcers can be:

  • continuous rubbing against misaligned or sharp teeth, dentures, or braces
  • poor oral hygiene
  • oral thrush infection
  • viral infections
  • autoimmune diseases
  • oral cancer
  • gastrointestinal disease

Treatment and Prevention

Your dentist can recommend the best treatment for you, depending on the type of ulcer you have. They may refer you to a specialist if it is serious or prescribe tablets for an infection. Otherwise, a dentist can smooth out a tooth that may be causing ulcers, or adjust dentures and braces that may be causing recurring ulcers.

To prevent ulcers from coming back, make sure to take care of your oral hygiene and try to avoid triggers that previously caused an outbreak. Use a high-quality toothbrush to reduce the risk of injury or rubbing while cleaning your teeth, and be careful when you are brushing your teeth. Eating a diet high in vitamins A, C and E can significantly reduce the risk of mouth cancer.

Need an Appointment?

If recurring mouth ulcers have given you cause for concern, book an appointment with Dentrix Dental today!