Canker Sore - Symptoms and Causes

What Are Canker Sores?

Canker sores are small, shallow sores that form inside the mouth on soft tissues or at the base of the gums. Unlike cold sores, they don’t appear on the lips and cannot spread from person to person.

These sores (also known as aphthous ulcers) can be quite painful and may interfere with eating and speaking. Most heal naturally within one to two weeks without treatment.

If you have large or painful sores that don’t heal quickly, see a healthcare professional. Your doctor or dentist can provide proper diagnosis and treatment options for persistent cases.

Signs of Canker Sores

Small Mouth Sores

Small mouth sores are the most common type of canker sore. They typically have a round or oval shape, with a white or yellow center surrounded by a red border. These sores:

Are usually tiny in size
Have an oval shape with reddened edges
Heal completely without leaving scars in 7–14 days

Minor sores can appear inside the cheeks, under the tongue, on the inner lips, at the gum base, or on the soft palate.

Large, Painful Sores

Large painful sores are less frequent but more severe than small mouth sores. These uncomfortable ulcers:

Grow bigger and deeper than minor sores
Usually have a round shape with clear borders (though larger ones may have jagged edges)
Causes significant pain and discomfort
May require up to six weeks to heal completely
Can leave scarring after healing

Cluster Sores

Cluster sores are rare and typically develop in older adults, though they are not caused by any herpes virus. These distinctive sores:

Are extremely small (pinpoint-sized)
Form in groups of 10–100 sores that sometimes combine into one large ulcer
Have uneven borders
Heal without scarring within 1–2 weeks

When Medical Help is Needed

You should contact your doctor if you experience:

Unusually large mouth sores
Sores that keep coming back, with new ones forming before old ones heal
Sores that last longer than two weeks
Sores that extend to the outer edge of your lips
Pain that doesn’t improve with home treatment
Difficulty eating or drinking
High fever, alongside mouth sores

Visit your dentist if sharp teeth or dental devices seem to trigger your sores.

Causes

Canker sores develop from a variety of factors, though scientists haven’t identified a single definitive cause. Many people experience outbreaks due to different triggers at different times.

Several common triggers can lead to canker sore development:

Physical Trauma: Small injuries from dental procedures, aggressive tooth brushing, sports accidents, or biting your cheek.
Oral Products: Toothpastes and mouthwashes containing sodium lauryl sulfate.
Food Triggers: Sensitivity to certain foods such as chocolate, coffee, strawberries, nuts, spicy foods, and acidic foods.
Nutritional Deficiencies: Lack of vitamin B-12, zinc, folate, or iron.
Bacterial Factors: Allergic responses to mouth bacteria or Helicobacter pylori infection.
Hormonal Changes: Particularly during menstruation.
Stress: Emotional or psychological stress.

Certain health conditions are also associated with increased canker sore occurrence.

Celiac Disease: An autoimmune reaction to gluten.
Inflammatory Bowel Diseases: Including Crohn’s disease and ulcerative colitis.
Behçet’s Disease: A rare inflammatory condition affecting multiple body systems.
Immune System Issues: When the body mistakenly attacks healthy mouth cells.
Compromised Immunity: Weakened immunity leading to frequent, severe outbreaks.

Unlike cold sores, canker sores have no connection to herpes virus infections.

Risk Factors

Canker sores can affect anyone, but certain groups face higher risks:

Age and Gender: Teens and young adults experience it more frequently, with females having a higher occurrence rate.
Family History: People with relatives who have canker sores.
Genetic Factors: The condition may run in families due to inherited traits.
Environmental Triggers: Family members might share exposure to similar foods or allergens that cause outbreaks.

Prevention

Canker sores can return again and again. However, several steps may help reduce how often they appear.

Food Choices

Avoid irritating foods like nuts, chips, and pretzels. You should also skip salty items and acidic fruits like pineapple, grapefruit, and oranges.
Skip any foods that trigger your personal sensitivities or allergies. Also, include plenty of fruits, vegetables, and whole grains to prevent nutrient deficiencies.

Maintain Good Oral Care

Make a habit of brushing your teeth regularly after each meal. Also, floss once daily and use a soft-bristled toothbrush to protect your mouth tissues.
You should also avoid toothpastes and rinses containing sodium lauryl sulfate.

Additional Protective Measures

If you wear braces or other dental devices, ask about orthodontic wax to cover sharp edges.
Lastly, practice stress management techniques like meditation or guided imagery if stress seems to trigger your canker sores.

Canker Sore – Symptoms and Causes