Updated on February 22, 2024
5 min read

What Are Canker Sores?

NewMouth is reader supported. We may earn a commission if you purchase something using one of our links. Advertising Disclosure.

What are Canker Sores? Where Do They Form?

Canker sores (aphthous ulcers) are small, shallow, and painful lesions that develop on the lips or inside the mouth. They appear as small round lesions with a white center (scientifically known as “slough”) and a red border (inflamed tissue).

The sores are a mixture of fluids, white blood cells, and bacteria. In some cases, canker sores can be as large as a quarter.

Canker sores don’t form outside of the mouth. Instead, they form in the following areas:

  • The base of the gums
  • Inside the cheeks
  • Inside of the lips (inner lip)
  • On the soft palate (back of the roof of the mouth)
  • On or under the tongue

What Causes Canker Sores?

Common causes of canker sores include:

1. Poor Oral Hygiene

Poor oral hygiene allows bacteria to develop in the mouth. Maintaining good oral hygiene prevents this from happening.

Keeping the mouth healthy includes:

  • Brushing twice a day
  • Flossing at least once a day
  • Rinsing the mouth regularly

Limiting hard, crunchy, unhealthy, or irritating foods (acidic) is helpful in preventing canker sores.

2. Oral Injuries

Oral injuries have many causes. These include:

  • After having dental work done
  • Sports injuries
  • Excessively brushing the teeth
  • Small cuts
  • Accidental cheek biting
  • Poor-fitting dentures
  • Braces
  • Fractures

Sustaining an oral injury through any of these means can increase the risk of developing sores.3,5

3. Food Allergies

Allergic reactions to food can cause the formation of canker sores.

These foods include:

  • Acidic foods
  • Spicy foods
  • Dairy
  • Nuts
  • Gluten

4. Toothpaste

Toothpaste containing sodium lauryl sulfate (SLS) can cause canker sores. SLS is known to irritate the tissues inside the mouth and gums.

If ulcers are recurrent, toothpaste is likely the culprit.

5. Nutritional Deficiencies

Excessive intake of sugar, processed foods, and citrus fruits can cause aphthous ulcers.

Some people recommend eating salads with raw onions because they contain sulfur, which has antibacterial effects.

6. Hormonal Imbalances

Hormonal imbalances can increase inflammation in and around the mouth. Causes include:

  • Puberty
  • Menopause
  • Menstrual cycles

7. HIV Infection

People with HIV/AIDS may develop severe sores more frequently than those without the virus.

Canker sores aren’t a symptom of human immunodeficiency virus (HIV), which is a virus that breaks down cells in the immune system. Rather, it’s a side effect of immune system impairment.

8. Stress and Fatigue

Emotional or physical stress can cause canker sores in some people because excessive stress increases inflammation.

9. Diseases

Frequent canker sores can occur with certain diseases and chronic health conditions.

These health conditions include, but aren’t limited to:

  • Inflammatory bowel diseases
  • Celiac disease (an intestinal disorder caused by gluten intolerance)
  • Behcet’s disease (causes inflammation around the entire body)
  • Lupus (an autoimmune disease that causes the body to attack the organs and tissues)

10. Vitamin Deficiencies

The body needs a proper balance of acidity, minerals, and alkalinity to avoid canker sores.

You may get canker sores if you’re deficient in:3,4

  • Iron
  • Zinc
  • Vitamin B12
  • Folic acid
  • Calcium

What Gets Rid of Canker Sores Fast?

Regardless of your treatment, canker sores don’t disappear within 24 hours. However, there are ways to avoid prolonging the healing stage.

You can use over-the-counter drugs and mouth rinses like:

  • Fluocinonide — Lidex (Fluocinonide) and Vanos mouth rinses
  • Hydrogen peroxide products Orajel Antiseptic Mouth Sore Rinse™ and Colgate® Peroxyl®
  • Tetracycline — A medication typically prescribed if you frequently get canker sores
  • Ibuprofen — Ibuprofen or other over-the-counter (OTC) pain relievers can reduce swelling, discomfort, and pain

Doctors advise against popping canker sores. This can be extremely painful.

It’s important to know that one possible side effect of tetracycline is a fungal infection called oral thrush. Ironically, oral thrush can lead to mouth sores.

Listen In Q&A Format

Canker Sores Types, Causes, and How to Get Rid of Them
NewMouth Podcast

Canker Sores vs. Cold Sores (Herpes)

Canker sores aren’t cold sores. They are noncontagious inflammations rather than infections.

The herpes simplex virus type 1 (HSV-1) is a highly contagious infection that causes cold sores (fever blisters). Cold sores are small, fluid-filled blisters that usually appear on the hard part of the gums or the outside of the lips.

Cold sores spread through close personal contact. This includes:

  • Kissing
  • Hugging
  • Handshaking
  • Sharing drinks
  • Sharing utensils

Herpes is a lifelong disease with no cure.

Symptoms of a Canker Sore

During the formation of a canker sore, it isn’t uncommon to feel discomfort around the infection.

Symptoms that a canker sore is beginning to form include:

  • Irritation
  • Tingling
  • Burning sensations

If you have a severe case of canker sores, you may experience other symptoms, which include:

  • Swollen lymph nodes
  • Fever
  • Sluggishness 

Natural Canker Sore Remedies

You can use a few natural home remedies to help speed up the healing process and decrease irritation. These include:

  • Suck on ice chips and/or Zinc lozenges to relieve pain and discomfort
  • Use a mouth rinse and toothpaste that doesn’t contain sodium lauryl sulfate
  • Rinse your mouth a few times each day with warm salt water or a baking soda rinse (one teaspoon per half cup of warm water) for a few minutes
  • Eat salads that contain raw onions
  • Drink chamomile tea to soothe canker sore discomfort (German chamomile contains anti-inflammatory and antiseptic properties)

7 Ways to Prevent Canker Sores

In most cases, canker sores are a natural part of life. However, if you develop sores frequently, there are ways to prevent them from developing.

Prevention tips include:

  1. Avoid or limit your intake of spicy foods, acidic fruits, and other acidic drinks (e.g., coffee and fruit juices)
  2. Take a multivitamin every day
  3. Take a 1000 mcg dose of vitamin B12 at night to reduce and prevent canker sore breakouts
  4. Don’t use dental products that contain sodium lauryl sulfate
  5. Chew less gum to prevent irritation
  6. Brush and floss your teeth regularly to remove bacteria, food particles, and plaque in your mouth
  7. Use a soft-bristled toothbrush and try to brush after each meal (if you get canker sores often)


Canker sores are small, painful lesions that develop inside the mouth. They can be small or large and typically have a white, gray, yellow, or red border.

There are three types of canker sores. Each one can vary in size, discomfort, and healing duration:

  • Minor sores can heal within two weeks
  • Major sores can last for months
  • Herpetiform sores require treatment

Most canker sores go away on their own within a week. If they last longer than two weeks, seek treatment.

Last updated on February 22, 2024
6 Sources Cited
Last updated on February 22, 2024
All NewMouth content is medically reviewed and fact-checked by a licensed dentist or orthodontist to ensure the information is factual, current, and relevant.

We have strict sourcing guidelines and only cite from current scientific research, such as scholarly articles, dentistry textbooks, government agencies, and medical journals. This also includes information provided by the American Dental Association (ADA), the American Association of Orthodontics (AAO), and the American Academy of Pediatrics (AAP).
  1. Balch, P.A. Prescription for Nutritional Healing. Avery, a Member of Penguin Group (USA) Inc., 2010.
  2. Zand et al. Smart Medicine for a Healthier Child: a Practical A-to-Z Reference to Natural and Conventional Treatments for Infants and Children. Avery, 2004.
  3. Aphthous Stomatitis.” Aphthous Stomatitis – an Overview | ScienceDirect Topics.
  4. Edgar et al. “Recurrent Aphthous Stomatitis: A Review.” The Journal of Clinical and Aesthetic Dermatology, Matrix Medical Communications, Mar. 2017.
  5. Scully, C., and Shotts, R. “Mouth Ulcers and Other Causes of Orofacial Soreness and Pain.” Western Journal of Medicine, Copyright 2001 BMJ Publishing Group, 2001.
  6.  “Canker Sores/Recurrent Aphthous Stomatitis (RAS) : Evidence-Based Practice.” FPRP, 1Bronx Lebanon Hospital Center.
linkedin facebook pinterest youtube rss twitter instagram facebook-blank rss-blank linkedin-blank pinterest youtube twitter instagram