Why Do Canker Sores Appear?

Canker sores are benign ulcers that can appear anywhere on oral cavity mucosa. We'll review its causes and some preventive measures here.
Why Do Canker Sores Appear?

Last update: 04 March, 2021

Have you ever wondered why canker sores appear? Most people who’ve experienced the discomfort and sensitivity that canker sores produce in the area don’t know what causes them. That’s why people want to avoid them at all costs!

Also known as mouth ulcers or aphthous ulcers, they’re usually whitish or reddish sores that appear anywhere on oral cavity mucosa, such as on the cheeks, tongue, or gums.

Although canker sores aren’t contagious, they’re quite bothersome and are about half an inch in size. A study published in the Western Journal of Medicine (WJM) indicates that approximately 20% of the world’s population suffers from canker sores on a regular basis. So, they’re the most common oral lesion after cavities.

Why do canker sores appear? Possible causes

A woman with canker sores.
These bothersome sores can cause painful eating or speaking. They’re the result of trauma, local infections, and other factors.

The causes of the onset of canker sores can be very varied. Here are the most common, according to the WJM:

  • Prolonged stress
  • Having suffered an infection, such as herpes, chickenpox, or fungal infections, among others
  • Not getting enough vitamins and minerals from the diet, which weakens the immune system
  • Abrasions due to prostheses or orthodontic appliances, such as braces
  • Bites
  • Hormonal changes, as a publication from the Institute for Quality and Efficiency in Health Care states
  • Allergies
  • Side effects of drugs
  • Stomatitis
  • Tobacco

Apart from these causes, some systemic diseases can also lead to them. For example, Crohn’s disease can cause canker sores.

The immune system can weaken due to different reasons, such as the flu, immunosuppressive treatments, and autoimmune conditions, among others.

The sources cited above state that a B vitamin deficiency directly affects oral health. Thus, it ends up causing ulcers. Therefore, foods rich in vitamins and minerals are essential for oral health.

This article may interest you: 5 Ways to Cure Canker Sores Quickly

Duration of canker sores

After a week or two, the sores usually disappear on their own without leaving scars. If they don’t disappear or change their size in 15 days, it’s very important to go see a dentist, as they may be a sign of another condition.


There are drugs that relieve the discomfort and pain canker sores cause. The dentist will recommend the most appropriate one, depending on each case. A 2014 study confirmed that the use of medications such as antiseptics and anti-inflammatory drugs can help relieve discomfort.

Likewise, mouthwash can provide temporary relief. Another option is topical hyaluronic acid that accelerates the healing process and proves helpful for these injuries. Ask your dentist for advice on its use.

According to popular beliefs, some home treatments can help relieve pain and make the sores heal faster. For example, mint tea and water and salt water rinses.

However, beyond the analgesic and anti-inflammatory effects of mint a study published in the Journal of the International Society of Sports Nutrition stated, these options lack scientific evidence regarding their safety and efficacy for the treatment of canker sores.

How to prevent canker sores

A man brushing his teeth.
Constantly cleaning your mouth is often enough to prevent the appearance of canker sores.

Although it isn’t 100% possible to prevent these ulcers, certain habits can help reduce the risk of their appearance. The studies we cited above mention the following:

  • Avoid spicy or hard foods
  • Maintain good oral hygiene
  • Eat a balanced diet
  • Drink enough water every day
  • Avoid intentionally biting your lips, as many people tend to do so when they’re nervous or anxious

In addition to these daily actions, some recommend placing wax on braces or other orthodontic appliances the first days of use in order to avoid rubbing that can lead to sores. However, it’s a good idea to follow your dentist’s instructions regarding this particular issue.

Why canker sores appear – they’re usually nothing to worry about

Most of the time, canker sores are benign and disappear in a short time. However, they can also be the secondary symptom of certain diseases, which increases their recurrence. Therefore, if you get them constantly or if they’re big or very painful, you should consult your doctor or dentist to get them checked out.

You should remember that it’s a good idea to follow conservative treatment and avoid home remedies as much as possible. In any case, if the discomfort doesn’t go away, consult your dentist to discover why these ulcers appear in your mouth and how to cure them.

  • Scully C, Shotts R. Mouth ulcers and other causes of orofacial soreness and pain. West J Med. 2001;174(6):421–424.
  • InformedHealth.org [Internet]. Cologne, Germany: Institute for Quality and Efficiency in Health Care (IQWiG); 2006-. Canker sores (mouth ulcers): Overview. 2019 Aug 15. Available from: https://www.ncbi.nlm.nih.gov/books/NBK546250/
  • Altenburg A, El-Haj N, Micheli C, Puttkammer M, Abdel-Naser MB, Zouboulis CC. The treatment of chronic recurrent oral aphthous ulcers. Dtsch Arztebl Int. 2014;111(40):665–673. doi:10.3238/arztebl.2014.0665
  • Meamarbashi, A., & Rajabi, A. (2013). The effects of peppermint on exercise performance. Journal of the International Society of Sports Nutrition, 10(1), 15. https://doi.org/10.1186/1550-2783-10-15