Canker Sores vs. Cold Sores

Edited by Mirabella Chan

Both canker sores and cold sores can be painful and uncomfortable lesions that pop up in or around the mouth. Although they can be confusing to differentiate, they're quite different in terms of their causes, symptoms, prevention and treatment. Keep reading to find out how you can differentiate between these two common bothersome mouth sores.


The cause of canker sores (known as aphthous ulcers) is unknown. They are an NOT caused by an infection, and although their cause is unknown, they are most commonly thought to be associated with factors such as local trauma in the area and stress. Other factors that can play a role include allergies, genetics, nutritional deficiencies, certain foods, hormonal changes, etc. There are three types of aphthous ulcers: minor, major and herpetiform. The most common (70-80% of cases) are minor aphthae.

The development of cold sores (known as herpes labialis) is due to the herpes simplex virus (HSV). HSV-1 is most commonly transmitted through saliva and causes most oral herpes infections, whereas HSV-2 is present in genital secretions and causes the majority of genital herpes cases. Both types of HSV can cause primary and recurrent infections. Although HSV-1 mainly causes oral infections and HSV-2 mainly causes genital infections, both HSV-1 and HSV-2 can cause infections in oral or genital regions. Oral infections of HSV, which is what cold sores are, most commonly affect the vermillion border of the lips. Less commonly, oral infections can occur in the hard palate of the mouth, chin or oral mucosa. The virus can be transmitted through oral contact and as well as contact with the virus in sores, saliva and surfaces in or around the mouth. Transmission can also occur through sharing cosmetics, razors, utensils, etc. with an infected individual.


Canker Sores

Minor aphthae are small, round/oval, clearly defined and painful ulcers that are usually smaller than 1 cm in diameter and have pseudomembranes that are whitish-grey in colour. The lesions can appear on their own or as multiple ulcers, and are usually on movable oral mucosa such as the mucosa of lips/cheeks, the floor of the mouth, underneath the tongue and on the soft palate. An uncomfortable sensation might occur in the area a few days before the actual appearance of the canker sore.

Red Flags for Referral

  • Pain is severe enough that patient isn’t eating

  • Diameter of ulcer > 1 cm

  • Duration of ulcer is longer than 14 days

  • More than 5 ulcers are present

  • Multiple clusters of ulcers have coalesced into an irregularly shaped lesion

  • History of having ulcers that last more than 14 days, heal with scarring and recur 6-12 times per year

  • Fever, joint pan or ulceration on any other surface such as skin, eye, genitalia

  • Red, white patches on oral mucosa that can be painful, swollen, or bleeding

  • Ulcer on roof of mouth or gums

  • HIV, other immunodeficiency diseases, IBD, Behcet syndrome or lupus

  • Fever, pharyngitis, and adenitis

  • First ulcer that occurs later in life (over the age of 30)

Cold Sores

Primary infections with HSV can cause common cold symptoms, such as weakness, fever, chills, muscle aches, and painful vesicles or blisters and ulcerative erosions on the tongue, palate, gingiva, mucosa and lips, which occurs 1-26 days after contracting the virus. The lesions rupture, which leaves small ulcers that are covered by pseudomembranes and surrounded by redness. The primary infection lasts 1-3 weeks, but the virus can still be shed for up to 23 days. Some patients go on to have recurrent episodes throughout their life (up to 1-6 per year), whereas other patients might never have a second infection at all. A tingling, itching or burning sensation might occur in the location of the eruption 2-24 hours before a recurrent infection occurs. The recurrent lesion occurs in 1-2 days, papules become vesicles within hours and go through the stages of ulceration, crusting and healing over 72-120 hours.

Red Flags for Referral

  • Lesion present for more than 14 days

  • Lesion is excessively red, swollen, or contains pus

  • Lesions occur more than 6 times per year

  • Systemic symptoms (e.g. fever, swollen glands)

  • Patient is immunocompromised


Tips on how to prevent canker sores and cold sores from occurring

Canker Sores

  • Take extra care while chewing; don't bite inside of cheeks

  • If there are teeth or dental work with sharp points, see dentist to make the point less irritating

  • Some people have fewer canker sores when they use toothpaste that doesn't contain sodium lauryl sulfate, an ingredient found in most toothpastes

  • Reduce stress, improve diet, good sleep hygiene, physical activity, relaxation

  • Correct any nutritional deficiencies

  • Avoid cow's milk or gluten if patient has an allergy or hypersensitivity

Cold Sores

  • Reduce stress, improve diet, good sleep hygiene, physical activity, relaxation

  • Avoid sharing forks, spoons, drinking containers, razors or towels with anyone until blister is healed

  • Protect areas from sun exposure, especially when at the beach or skiing (SPF 30 or higher should be applied to lips and face 30 minutes prior to exposure)

  • Prophylactic treatment with an antiviral prior to dental procedures

  • Avoid spreading to others by frequent handwashing and avoiding skin-to-skin contact with others until the blister is healed


Non-Pharmacologic Treatment

Canker Sores

  • Avoid foods that cause pain and are hard, crusty, spicy, salty, spicy, acidic or difficult to chew

  • Limit all oral trauma as much as possible

  • Maintain regular daily oral hygiene: brush twice daily, floss and professional dental cleaning every 6 months

  • Aphthae can be cleansed by rinsing mouth with salt and water

Cold Sores

  • Gentle washing of lesions with mild soap and water

  • Soak area with cool, tap-water compresses

  • Avoid excessive touching of lesion

  • Wash hands frequently to prevent autoinoculation and spread

Pharmacologic Treatment

Canker Sores

Topical protectants (hydroxypropyl cellulose, carboxymethyl cellulose)

  • Mucosal adherent agents over the ulcer for temporary pain relief and protection

Topical anesthetics (benzocaine, lidocaine)

  • For temporary pain relief

Topical corticosteroids (clobetasol, fluocinonide, triamcinolone)

  • To help relieve pain & inflammation

Local antibiotics (tetracycline 5% or minocycline 0.2% mouthwashes)

  • Antibiotic mouthwashes to reduce pain, ulcer size and duration of canker sores

  • May increase risk of fungal infections, skin reactions, sore throat, stained teeth or development of bacterial resistance

Cold Sores

Topical protectants (allantoin, calamine, cocoa butter, petrolatum, zinc oxide)

  • To help prevent cracking and excessive drying of lesions

Topical anesthetics (benzocaine, camphor, lidocaine, menthol)

  • For mild pain for short amount of time

Oral analgesics (acetaminophen, ibuprofen, naproxen)

  • For moderate-severe pain, used for up to 3 days

Topical antivirals (docosanol)

  • To prevent HSV from spreading to healthy cells and reduce healing time or stop discomfort sooner

Oral antivirals (acyclovir, famciclovir, valacyclovir)

  • For treatment and prophylaxis of cold sores

Cold sores and canker sores are very common oral conditions that affect both children and adults. Many people have to deal with these lesions often and don’t know the difference between them. As pharmacists, we can help patients distinguish between the two conditions and educate patients on how they can prevent and treat them.

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  1. Conklin J. Cold Sores (Herpes Labialis). In: Compendium of Pharmaceuticals and Specialties. Canadian Pharmacists Association. Updated September 18, 2018. Accessed April 1, 2021.

  2. Markarian A. Aphthous Ulcers (Canker Sores). In: Compendium of Pharmaceuticals and Specialties. Canadian Pharmacists Association. Updated March 19, 2018. Accessed April 1, 2021.

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