A sore mouth can make eating, talking, and smiling uncomfortable — and it’s easy to lump every mouth sore into one category. But canker sores and cold sores are two very different conditions with different causes, different treatments, and one very important distinction: whether they’re contagious. Knowing which one you’re dealing with helps you choose the right relief and know when it’s time to call us.
What Is a Canker Sore?
Canker sores (called aphthous ulcers by dentists) are small, shallow ulcers that form inside the mouth — on the inner cheeks, lips, tongue, or the floor of the mouth. They appear as a white or yellow center surrounded by a red border, and while they can be quite painful, especially when eating spicy or acidic foods, they are not contagious. Canker sores affect a large share of the population at some point, often starting in childhood or the teenage years, and tend to run in families.
What Is a Cold Sore?
Cold sores (also called fever blisters) are caused by the herpes simplex virus (usually HSV-1), which most people are exposed to early in life through everyday contact like sharing utensils or a kiss from a family member. Unlike canker sores, cold sores form on or around the outside of the lips and skin, starting as a cluster of small, fluid-filled blisters that tingle or burn before they appear. The virus stays dormant in the body afterward and can reactivate periodically — which is why cold sores tend to come back in the same spot. Cold sores are contagious, especially while blisters are open and weeping.
Key Differences at a Glance
- Location: Canker sores form inside the mouth; cold sores form on or around the outside of the lips.
- Appearance: Canker sores are flat ulcers with a white or yellow center; cold sores are raised, fluid-filled blisters that eventually crust over.
- Contagious? Canker sores are not contagious. Cold sores are, particularly when blisters are open.
- Cause: Canker sores are linked to minor mouth injury, stress, certain foods, and nutritional gaps; cold sores are caused by a herpes virus infection.
- Healing time: Canker sores typically heal in one to two weeks; cold sores often take two to four weeks to fully resolve.
What Triggers Flare-Ups?
Canker sores are often set off by minor trauma (like accidentally biting your cheek or a rough spot from braces or a dental appliance), stress, hormonal changes, acidic or spicy foods, or low levels of iron, vitamin B12, or folate. Cold sores, on the other hand, tend to flare up with stress, illness or fever, sun exposure, hormonal shifts, and a dip in immune function — the virus is always present in the body; something simply has to wake it up.
Finding Relief at Home
For canker sores, over-the-counter numbing gels, a saltwater or antimicrobial mouth rinse, and avoiding acidic or spicy foods can ease discomfort while the sore heals on its own. For cold sores, over-the-counter antiviral creams work best when applied at the very first tingle, and a cold compress can reduce swelling. If sores are unusually large, keep coming back frequently, or aren’t healing within a couple of weeks, it’s worth having us take a look — prescription treatments are available for both conditions.
How We Can Help
At Fridman Family Dental Care, we help patients tell the difference between canker sores, cold sores, and other causes of mouth irritation, and we can recommend or prescribe treatments to speed healing and reduce how often they recur. If a rough tooth, ill-fitting appliance, or braces bracket is triggering repeated canker sores, we can smooth or adjust it as part of your routine preventive care visit. As a family dental practice, we see this concern often and are glad to help patients of any age find relief. For a closer look at the underlying causes and treatment evidence, see our companion clinical review of recurrent aphthous stomatitis and herpes labialis.
When to See Us
Most canker sores and cold sores heal on their own within a couple of weeks. But see us if a sore lasts longer than two to three weeks, is unusually large or painful, keeps coming back frequently, or is accompanied by fever or swollen glands — these can be signs that something more should be evaluated. Call Fridman Family Dental Care in Valencia, CA at (661) 254-3700 or request an appointment online.
