Canker Sores vs. Cold Sores
Canker sores are non-contagious ulcers inside the mouth, while cold sores are contagious herpes simplex virus blisters typically on the lip border. Treatment and prevention differ entirely.
Key Facts
- Canker sores (aphthous ulcers) are not viral and not contagious
- Cold sores are caused by HSV-1 in most cases
- Cold sores are highly contagious, especially during the blister phase
- Recurrent canker sores can signal B12, iron, or folate deficiency
What Is a Canker Sore?
An aphthous ulcer is a shallow, round, white-to-yellow lesion with a red halo on movable mucosa (cheek, tongue, inner lip). Triggers include stress, minor trauma, SLS toothpaste, and nutrient deficiency.
What Is a Cold Sore?
A cold sore is a fluid-filled blister cluster on the vermillion border of the lip caused by HSV-1 reactivation. It progresses through tingling, blister, ulcer, crust, and healing phases over 7–10 days.
Why It Matters
Misidentifying a cold sore as a canker sore can lead to spreading the virus through kissing, shared utensils, or oral sex. Recurrent canker sores warrant a workup for systemic causes.