Canker Sores (Aphthous Ulcers)

Understanding Canker Sores and How They Are Treated

What Are Canker Sores?

Canker sores, also known as aphthous ulcers, are small, shallow sores that develop inside the mouth. They most commonly appear on the:

  • Inside of the lips
  • Inside of the cheeks
  • Tongue
  • Floor of the mouth
  • Soft palate

Unlike cold sores, canker sores are not contagious and do not occur on the outside of the lips.

Although they can be painful, most canker sores heal on their own without leaving scars.

What Causes Canker Sores?

The exact cause of canker sores is not fully understood.

Researchers believe that several factors may contribute, including:

  • Minor injury to the mouth
  • Emotional stress
  • Hormonal changes
  • Certain foods
  • Vitamin B12 deficiency
  • Folate deficiency
  • Iron deficiency
  • Food sensitivities
  • Family history
  • Changes in the immune system

In many people, no specific cause can be identified.

Common Triggers

Some people notice canker sores after:

  • Accidentally biting their cheek or lip
  • Brushing too aggressively
  • Wearing braces or dentures
  • Dental procedures
  • Eating acidic foods
  • Eating spicy foods
  • Periods of increased stress

Triggers vary from person to person.

Symptoms

Most canker sores are:

  • Round or oval
  • White, yellow, or gray in the center
  • Surrounded by a red border
  • Painful, especially while eating, drinking, or brushing

Some people experience a burning or tingling sensation before the sore appears.

Types of Canker Sores

Minor Canker Sores

Minor aphthous ulcers are the most common type.

They are usually:

  • Less than 1 centimeter (0.4 inches) in diameter
  • One to five sores at a time
  • Healed within 7–14 days
  • Not associated with scarring

Major Canker Sores

Major aphthous ulcers are:

  • Larger
  • Deeper
  • More painful
  • Slower to heal

Healing may take several weeks and may leave a scar.

Herpetiform Canker Sores

Despite the name, herpetiform ulcers are not caused by the herpes virus.

They appear as numerous tiny ulcers that may merge into larger painful areas.

Are Canker Sores Contagious?

No.

Canker sores cannot spread from one person to another through:

  • Kissing
  • Sharing utensils
  • Sharing drinks
  • Close personal contact

This is one of the biggest differences between canker sores and cold sores.

Canker Sores vs. Cold Sores

Although they are often confused, they are different conditions.

 

Canker SoresCold SoresOccur inside the mouthUsually occur on the lips or around the mouthNot contagiousHighly contagiousNot caused by a virusCaused by herpes simplex virus (HSV-1)Heal on their ownHeal on their own but may recur throughout life

 

How Are Canker Sores Diagnosed?

Most canker sores are diagnosed through:

  • Medical history
  • Clinical examination

Additional testing may be recommended if sores:

  • Last longer than two weeks
  • Occur very frequently
  • Are unusually large
  • Are associated with fever, weight loss, or other unexplained symptoms

Persistent mouth ulcers should always be evaluated.

Treatment

Most canker sores heal without treatment.

Treatment focuses on reducing pain and improving comfort.

Your dentist or healthcare provider may recommend:

  • Saltwater rinses
  • Baking soda rinses
  • Protective oral gels
  • Prescription topical corticosteroids
  • Pain-relieving mouth rinses
  • Avoiding foods that irritate the sore

Good oral hygiene should be maintained while the sore heals.

Foods That May Increase Discomfort

During healing, some foods may worsen pain, including:

  • Citrus fruits
  • Tomatoes
  • Pineapple
  • Spicy foods
  • Salty foods
  • Crunchy foods
  • Very hot beverages

Choosing softer, less acidic foods may improve comfort.

When Should You See a Dentist or Physician?

Seek professional evaluation if a mouth sore:

  • Lasts longer than two weeks
  • Is unusually large
  • Recurs frequently
  • Makes eating or drinking difficult
  • Is accompanied by fever
  • Is associated with swollen lymph nodes
  • Appears together with skin rashes or other unexplained symptoms

Persistent oral ulcers require evaluation because other conditions can resemble canker sores.

Can Canker Sores Be Prevented?

Although prevention is not always possible, you may reduce your risk by:

  • Brushing gently with a soft-bristled toothbrush
  • Avoiding foods that trigger outbreaks
  • Managing stress
  • Eating a balanced diet
  • Correcting vitamin deficiencies when recommended by your healthcare provider
  • Keeping braces or dentures properly adjusted

Common Myths

"Canker sores are contagious."

False.

They cannot spread from one person to another.

"Poor oral hygiene causes canker sores."

False.

Although good oral hygiene supports overall oral health, canker sores are not caused by inadequate brushing or flossing.

"Every mouth ulcer is a canker sore."

False.

Mouth ulcers may result from trauma, infections, autoimmune diseases, medication reactions, or oral cancer. Persistent sores should always be evaluated by a healthcare professional.

Key Takeaways

✔ Canker sores are common ulcers that develop inside the mouth.

✔ They are not contagious.

✔ Most heal naturally within one to two weeks.

✔ Stress, minor injury, and certain foods may trigger outbreaks.

✔ Treatment focuses on relieving pain while the ulcer heals.

✔ Mouth sores that persist longer than two weeks should be evaluated by a dental or medical professional.

References

  1. American Dental Association. Canker Sores (Aphthous Ulcers). https://www.ada.org
  2. National Institute of Dental and Craniofacial Research. Mouth Sores. https://www.nidcr.nih.gov
  3. American Academy of Oral Medicine. Canker Sores (Recurrent Aphthous Stomatitis). https://www.aaom.com
  4. Mayo Clinic. Canker Sore. https://www.mayoclinic.org
  5. World Health Organization. Oral Health. https://www.who.int/health-topics/oral-health