Why Do Mouth Sores Happen?

Mouth sores are a common problem that can affect people of all ages. While the cause of mouth sores can vary from person to person, there are some general causes that are known to contribute to the development of mouth sores. In this article, we will explore some of the most common causes of why mouth sores happen. We will also provide information on how you can treat and prevent mouth sores from occurring.

What Are Mouth Sores?

A mouth sore is a lesion that occurs in the mouth. These lesions are usually painful and can make daily activities like eating, drinking, and speaking difficult. Different types of mouth sores include:

  • Canker sores - Canker sores are small ulcers that aren't contagious and form on the soft tissues in the mouth. They typically heal within two weeks. 
  • Cold sores - Cold sores, or fever blisters, are small blisters that form on the lips or around the mouth. Cold sores typically heal within two weeks. 
  • Viral infection sores - Sores from viral infections, like a sore throat, occur when you're sick and typically heal within two weeks.
  • Cancer mouth sores - Cancer mouth sores are painful lesions that occur when the tissues that protect the inside of your mouth become inflamed and damaged by radiation, chemotherapy, and sometimes by immunotherapy. 

What Causes Mouth Sores?

There are many different reasons why mouth sores happen. They may be caused by infection, inflammation, or injury to the tissues in the mouth. Sometimes, mouth sores are a sign of an underlying medical condition such as a food allergy, but they can also be caused by how your body responds to certain medications, among other reasons.

Certain Medications

While it is rare for certain medications to cause mouth sores, a few, including over-the-counter medications, can cause them. According to GoodRx Health, medications such as methotrexate, an immunosuppressant used to treat many autoimmune disorders, can cause mouth sores. 
Painkillers, such as ibuprofen, naproxen, and aspirin, as well as antibiotics like amoxicillin and ampicillin, have also been known to cause mouth sores. Finally, anti-seizure medication like phenytoin can cause mouth sores in high dosages.

Cheek Biting

Mouth sores can occur following an injury to the soft tissues in the mouth, such as damage from biting your cheek. Often the result of an accident, like falling or eating too quickly, cheek biting can also occur during periods of high stress, anxiety, or depression.

Chronic cheek biting, or psychological-related biting, can occur without you being aware that it is happening until the inside of the cheek has sores. 

Canker sores are the result of cheek biting, and while they're painful and characterized by their white or yellowish color, they often heal on their own, without the need for medical attention.

Iron Deficiency

Another reason why mouth sores happen is an iron deficiency or anemia. If your diet lacks iron, red, flaky cracks can form at the corners of your mouth. Chapped lips exacerbate this symptom during cold weather. Iron deficiency can weaken the tissues in the mouth, making them more susceptible to developing sores and wounds.

Vitamin B Deficiency

Vitamin B12 is essential for the production of red blood cells and the maintenance of nerve tissue. When your body lacks vitamin B12, it produces red blood cells that are too large to function properly and tend to die sooner. As such, this condition is often associated with anemia, which can cause mouth sores to form.

Stress, Anxiety, or Depression

Similar to cheeking as a result of anxiety, mouth ulcers have been linked to our mental and physical well-being. According to a 2019 study, conditions like stress, distress, anxiety, depression, and loneliness can be linked to poor oral health. The researchers found a significant correlation between mouth ulcers and depressive symptoms, specifically as it relates to people who are genetically prone to developing mouth sores.


Burns from hot and acidic food or stomach acid can weaken and damage the tissues of the mouth. Additionally, chemical burns from harsh mouthwashes that contain a high level of alcohol  can also cause mouth sores when the alcohol content ranges from 10 to 26 percent.  


Until the inside of your mouth gets used to braces and develops scar tissue to protect itself, you're likely to develop traumatic ulcers when first wearing braces. Ulcers caused by braces usually only form in a single sore.

Gut Problems

Inflammatory bowel diseases (IBDs), like Crohn's disease and ulcerative colitis, can cause oral lesions to occur. In fact, 0.5%-9% of Crohn's disease patients experience oral lesions, and it's believed that inflammation caused by Crohn's disease can be linked to inflammation in the mouth.

Certain Autoimmune Disorders

Autoimmune disorders, such as pemphigus vulgaris, can cause blisters on the skin and mucous membranes of the body, including the mouth. The blisters are often caused by a trigger and will sometimes go away once the trigger is removed.

Kissing and Sharing Drinkware

Intimate contact with someone who has herpes simplex virus type 1 can result in cold sores. Cold sores, or fever blisters, as they're commonly referred to, are common viral infections that occur on and around the lips. They typically heal within two to three weeks.

Diseases that Cause Rashes

Several diseases, such as candidiasis, lichen planus, and leukoplakia, to name a few, can cause ulcers to form. They can also make it easier for sores to develop.

Poor Oral Hygiene

Gingiovostomatitis, caused by poor dental hygiene, can cause blisters to form on the lips and canker sores in the mouth. It's often the result of not brushing or flossing frequently enough.


Tobacco stomatitis, often referred to as smoker's mouth, is an inflammation of the mouth's mucus membranes. Tobacco stomatitis occurs from a combiniation of heat and chemicals in tobacco irritating the mucus membranes of your mouth. 

Mouth Cancer

One of the most common symptoms of mouth cancer is the presence of painful mouth sores that take longer than several weeks to heal, as well as unexplained, persistent lumps within the mouth that don't subside. These symptoms should be examined by a doctor.

Chemotherapy and/or Radiation

Mouth sores caused by chemotherapy or radiation can form inside of your mouth, lips, throat, and the rest of your GI tract. Chemotherapy and radiation are designed to target rapidly growing cells within the body. However, these treatments can't tell the difference between healthy cells – like the cells lining your GI tract – and cancerous cells, so both are affected.

Is There Anything You Can Do for Mouth Sores?

If you or a loved one are experiencing mouth sores, you can try a few simple home remedies that have been known to provide relief. However, before trying these solutions, it's important to consult with your doctor to ensure that these solutions won’t cause pain or irritation for your specific condition.

  • Baking soda rinse: Baking soda can be used to reduce inflammation and neutralize any acids that might be irritating your mouth. Mix a teaspoon of baking soda in a cup of water and swish it around your mouth for 30 seconds before spitting it out.
  • Ice chips (or cryotherapy): A simple, inexpensive way to reduce mouth sore inflammation is to chew on ice chips or suck on an ice pop. This method can be used during some cancer treatments to prevent mouth sores from happening.
  • Healios: Healios is a nutrient-based solution that directly addresses the damage in your mouth and helps with the healing of tissues that are sensitive to cancer treatments. If you’re curious about Healios, talk to your doctor to find out how you can  incorporate it into your supportive cancer care plan.
To find out more about how to reduce the negative effects of mouth sores caused by cancer treatments, visit Enlivity’s Patient Learning Center or contact Enlivity.
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