Both canker sores and cold sores are common, painful lesions that appear in or around the mouth, but they are fundamentally different conditions. Canker sores, known medically as aphthous ulcers, form inside the mouth on soft tissues. Cold sores, also called fever blisters, are caused by a viral infection and typically appear on the outside of the lips. Understanding their distinct cause and appearance helps determine the correct management strategy.
The Fundamental Difference: Cause and Contagion
Canker sores are not caused by a virus and are not contagious. Their exact cause is not fully known, but they are linked to an immune response triggered by factors like minor injury to the mouth lining, emotional stress, or nutritional deficiencies such as low levels of B12 or iron. They are considered non-transmissible oral lesions.
Cold sores are highly contagious lesions caused by the Herpes Simplex Virus type 1 (HSV-1). Once an individual is infected, the virus remains dormant in nerve cells and can reactivate periodically, causing an outbreak. The virus spreads easily through direct contact, such as kissing, or by sharing items like lip balm or drinking glasses when a sore is active.
Where and How They Appear
The location of the lesion is the most reliable way to differentiate the two conditions. Canker sores develop exclusively inside the mouth, appearing on the soft, movable tissues. These locations include the inner cheeks, the tongue, the soft palate, and the base of the gums.
A canker sore presents as a shallow, round, or oval ulcer. It has a white or yellowish center and is surrounded by a bright red, inflamed border. They usually appear singly or in small clusters and can range in size. Minor canker sores are the most common, typically healing in one to two weeks without scarring.
Cold sores almost always appear on the outside of the mouth, most frequently on or around the lips. An outbreak is often preceded by a tingling, itching, or burning sensation, known as the prodromal stage. The lesion then progresses into a cluster of small, fluid-filled blisters that eventually burst, leading to a shallow open sore that crusts over into a scab before healing.
Managing and Treating Each Type
Because their causes differ, treatment goals for canker sores are distinct. Treatment focuses on pain relief and reducing inflammation, as they typically resolve naturally within two weeks. Topical products containing local anesthetics like benzocaine or lidocaine can be applied directly to the sore to dull the pain.
A healthcare provider may prescribe a mouth rinse containing a steroid, such as dexamethasone, to reduce pain and inflammation if multiple sores are present. Avoiding known triggers, like acidic or spicy foods, along with using a saltwater or baking soda rinse, can help soothe the irritation.
Cold sore management centers on using antiviral medications to speed up healing and reduce the frequency of future outbreaks. Oral antiviral drugs like acyclovir, valacyclovir, or famciclovir are often prescribed and are most effective when started during the initial tingling stage. Topical antiviral creams, such as penciclovir, can also be applied to the blisters to shorten the duration of the outbreak.
Preventing transmission requires avoiding close contact like kissing when a sore is active. Since sunlight and stress can trigger recurrences, applying lip balm with sunscreen can help reduce the frequency of future outbreaks. Oral antiviral medications may also be used long-term as a preventative measure for people who experience frequent recurrences.