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Why Your Canker Sore (Probably) Isn’t Infected

A woman lifts her top lip to look at her infected canker sore.


Canker sores are painful even under the best of circumstances. But if you think you have an infected canker sore, you may feel unsure or scared. Let’s examine how to know if your canker sore is infected and what to do about it.

Is It a Canker Sore?

Canker sores are extremely common mouth ulcers. Sometimes referred to as aphthous ulcers, canker sores are shallow white or yellow lesions with a bright pink or red border.

Canker sores most often form inside the lips and cheeks, though they can affect other parts of the mouth as well, such as the uvula and the tongue. Canker sores usually measure between 1 and 4 mm in diameter, though some can grow even larger.

It’s important to note that canker sores are not contagious, and unlike cold sores, they don’t result from infection with a herpes virus. Instead, various triggers can cause canker sores, and they vary from person to person. A few common triggers include:

  • Excessive use of nonsteroidal anti-inflammatory drugs (NSAIDs) like Motrin and Aleve
  • Low levels of vitamin B12 or iron
  • High-acid foods like oranges, tomatoes, and unripe bananas
  • Autoimmune conditions
  • Chronic stress
  • Friction on the gums from braces and other orthodontic appliances

Common Canker Sore Misdiagnoses

The first thing to do if you suspect you have an infected canker sore is to make sure that the sore is, indeed, a canker sore! Here are a few common misdiagnoses.

Infographic: Why Your Canker Sore (Probably) Isn’t Infected

Cold Sores

Many people confuse cold sores and canker sores, but canker sores aren’t related to cold sores, which are caused by the herpes simplex virus, type 1 (HSV-1). Cold sores don't usually form inside the mouth. If you’ve never had one before, it’s not likely that your first cold sore would develop inside your mouth.

Oral Lichen Planus

Oral lichen planus is an immune system disorder that causes white, lacey patches and red sores to form throughout the mouth. Though both conditions are painful, canker sores appear only in one or a few spots at a time.

Oral Candidiasis

Oral candidiasis, also known as oral thrush, is a fungal infection that starts when Candida albicans begins to accumulate on the lining of the mouth. This infection isn’t dangerous, but it can cause discomfort. It’s most common in nursing babies, immunocompromised adults, and patients receiving mechanical ventilation.

Oral candidiasis can cause white lesions on the inner cheeks, roof of the mouth, gums, and tongue. But unlike canker sores, these patches tend to be slightly raised and scattered throughout the mouth.


Much like oral candidiasis, leukoplakia also causes white spots throughout the mouth. But unlike these other oral conditions, leukoplakia doesn’t cause any pain.

How to Tell if You Have an Infected Canker Sore

Once you’ve determined that a canker sore is what you’re dealing with, you need to figure out if it’s infected.

The extreme pain of a canker sore and the whitish-yellow tissue in the center can cause many people to think their mouth ulcer is infected. However, despite being raw and painful, canker sores rarely become infected.

Sometimes excessive bacteria in the mouth lead to the formation of canker sores in the first place, but this is usually due to a compromised immune system or poor oral hygiene.

Unusually large canker sores or canker sores that sustain further injury have a greater risk of infection. If you suspect you have an infected canker sore, consult with a healthcare professional. They can recommend an antiseptic wash for minor infections or prescribe an antibiotic if necessary.

What Else Can Cause Oral Infections?

Unfortunately, canker sores aren’t the only thing in your mouth that can become infected. If you have symptoms of an oral infection, here are a few other possible causes.

Infection After Wisdom Tooth Extraction

A wisdom tooth extraction is an invasive procedure that exposes the mouth to the possibility of infection. By its nature, the procedure results in some swelling and pain, which should subside after three to four days. If the symptoms persist or if you develop a fever, contact your dentist or surgeon to discuss whether you may have an infection that needs treatment.

Infected Oral Piercings

Piercings in the mouth can be particularly prone to infection due to the constantly moist environment and natural prevalence of bacteria.

During the first few weeks after you receive any new piercing, you’ll likely deal with some redness, swelling, and clear or white discharge. But if these symptoms extend beyond the first few weeks or if you develop worsening pain, excessive bleeding, pus, or a fever, your piercing is probably infected.

While mild piercing infections can be treated at home, you should always contact your piercer and a physician for guidance if you experience any concerning symptoms.

Canker Sore Treatment

Even if your canker sore isn’t infected, it can still cause a lot of pain and interfere with your life. Here are just a few ways you can diminish that pain as your canker sore heals.

Over-the-Counter Canker Sore Medications

You can find many canker sore therapies at your local drugstore, and none of them require a prescription.

Topical Creams and Ointments

Many topical creams, liquids, and ointments are made to create a protective barrier between your canker sore and the outside world. Products like Kank-A Mouth Pain Liquid and Orajel 4X use benzocaine to numb the canker sore, while others like Curoxen use only natural ingredients to reduce pain and encourage healing.


Canker sore patches form a film or covering over a canker sore to protect it from irritation from eating and talking. Zilactin-B is a gel that dries into a canker sore cover, and Hyland's Canker Sore Healing Dots are homeopathic tablets that include calendula, borax, and other natural ingredients.

Dental Products

Medications aren’t the only canker sore care products you can find at the pharmacy. Oral rinses like Colgate Peroxyl Antiseptic Mouth Sore Rinse and G-U-M Canker-X Gel approach canker sore treatment from an oral health perspective.

Natural Home Remedies for Canker Sores

Although many natural remedies for canker sores haven’t been clinically tested, many people swear by them. Some of the better home remedy options for canker sore treatment include:

  • Silver nitrate
  • Coconut oil
  • Salt water
  • Hydrogen peroxide
  • Baking soda
  • Essential oils

Treatment With Light

Light therapy offers yet another safe and effective option to treat canker sores. Clinical studies show that red light therapy immediately reduces the pain of canker sores and reduces healing time as well. The Luminance RED Mouth Sore Treatment Device is an FDA-registered device that uses red light therapy to target painful canker sores.

When To Contact a Doctor

With or without treatment, most canker sores resolve on their own within one to two weeks. If your canker sore persists longer than this or grows to be wider than 5 mm, you could be dealing with an infected canker sore or a complex canker sore.

Complex canker sores may also be accompanied by fever, swollen lymph nodes, and lethargy, and they can be a sign of autoimmune conditions, vitamin deficiencies, and allergies. So if you have a lingering or excessively large canker sore, regardless of whether you think it’s infected, be sure to contact a doctor or dentist for advice.

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