What are mouth sores?

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Mouth sores are small, painful sores that develop in the mouth, at the base of the gums or around the lips.

Mouth sores often seem to show up in your mouth out of nowhere. But one thing’s for sure: they can be painful, irritating, and at times, unsightly. If you’ve recently noticed a sore in your mouth, you might be wondering how it got there and how you can make it go away. Learn the most common types of mouth sores, possible causes, and how to treat mouth sores.

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What is a mouth sore?

Mouth sores are small, painful sores that develop in the mouth, at the base of the gums or around the lips. While often painful and annoying, they usually go away within one to two weeks. There are many different types of mouth sores, but the most common are canker sores, cold sores, and oral candidiasis or oral thrush.¹

Canker sores

Canker sores are the most common type of mouth sore. Experts estimate that around one out of every 10 people is affected.² Also known as aphthous mouth ulcers, canker sores are round, white sores with a red border that form inside the mouth.³ They can appear as a single sore or in a cluster. Depending on location and severity, canker sores can cause discomfort when eating, drinking, and talking.

Cold sores

Cold sores are fluid-filled blisters. They appear on the lips, chin, or cheeks. They’re caused by a viral infection. Though painful, cold sores are usually harmless. However, the infection can have serious health consequences if it affects people with impaired immune systems.⁴

Oral candidiasis

Oral candidiasis, or oral thrush, is a fungal infection common among denture wearers. People with weak immune systems tend to be the most susceptible, including young children, elderly adults, and people debilitated by disease. Thrush manifests itself with small white patches in the mouth, redness, and a painful burning sensation.⁵

What causes mouth sores?

Knowing what caused your mouth sores can help you treat them and avoid further irritation. While the exact cause of some types of mouth sores remains unknown, here are a few possible causes:


Various irritants can lead to canker sores, including:⁶

  • Cuts, burns, or bites while eating

  • Dental work

  • Hard brushing

  • Poorly fitting dentures

  • Acidic or spicy foods

  • A sharp or broken tooth

  • Braces or retainers

Poor oral hygiene

Failing to take proper care of your teeth and mouth can occasionally lead to mouth sores, especially oral candidiasis. It’s important to see your dentist regularly, brush twice a day for two minutes, and floss each day (yes, even if your mouth sores make it hurt).⁷

Stress & anxiety

Stress doesn’t just affect your mood—it can also impact your mouth.⁸

Are mouth sores contagious?

Some mouth sores are highly contagious. Cold sores are caused by a viral infection called herpes simplex, which is usually transmitted through saliva. At least half of all adults are infected with HSV, though most of the time it causes no symptoms⁹. Coming into contact with an infected person can cause cold sores. Cold sores are most infectious when they are blistering, so it’s important to avoid touching them.

Most other mouth sores are not contagious. Many tend to confuse canker sores with cold sores, but canker sores aren’t at all infectious. Neither is oral thrush.

How to treat mouth sores

In most cases, you just need to be patient and wait for the sore to go away. Most mouth sores go away on their own within two weeks. However, canker sores may require over-the-counter or prescription products.¹⁰

When to see your dentist about mouth sores

If it’s been more than a year since you’ve seen your dentist, make an appointment. With dental insurance, preventive care is usually covered. You’ll have the chance to consult your dentist about your mouth sore concerns then.

You should also see your dentist if your mouth sores have lasted longer than two weeks, even if they aren’t painful. Your dentist will be able to diagnose the problem based on appearance and location and come up with a treatment plan.

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Brought to you by The Guardian Life Insurance Company of America (Guardian), New York, NY. Material discussed is meant for general illustration and/or informational purposes only and it is not to be construed as tax, legal, investment or medical advice. This is not dental care advice and should not be substituted for regular consultation with your dentist. If you have any concerns about your dental health, please contact your dentist's office.


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  1. https://www.mouthhealthy.org/en/az-topics/m/mouth-sores (Last accessed February 2020)

  2. https://www.ncbi.nlm.nih.gov/books/NBK546250/, 2019

  3. https://www.mayoclinic.org/diseases-conditions/canker-sore/symptoms-causes/syc-20370615 (Last accessed February 2020)

  4. https://www.mayoclinic.org/diseases-conditions/cold-sore/symptoms-causes/syc-20371017?page=0&citems=10, 2018

  5. https://www.mouthhealthy.org/en/az-topics/t/thrush (Last accessed February 2020)

  6. https://www.mayoclinic.org/diseases-conditions/canker-sore/symptoms-causes/syc-20370615, 2018

  7. https://www.mayoclinic.org/diseases-conditions/oral-thrush/symptoms-causes/syc-20353533, 2018

  8. https://www.mayoclinic.org/diseases-conditions/canker-sore/symptoms-causes/syc-20370615, 2018

  9. https://www.medicalnewstoday.com/articles/172389, 2017

  10. https://www.mayoclinic.org/diseases-conditions/canker-sore/diagnosis-treatment/drc-20370620, 2018