Mouth Sores: Canker Sores, Cold Sores, and How to Tell Them Apart

Canker sores are small, shallow sores that develop inside the mouth — on the inner cheek, tongue, or the base of the gums — typically appearing as a white or yellow center surrounded by a red border. Unlike cold sores, canker sores only occur inside the mouth, never on the outer lip, and they're not caused by a virus, so they aren't contagious.

This is genuinely the most useful distinction to understand. Cold sores, caused by the herpes simplex virus, typically appear on or around the outer lip, often start as a cluster of small blisters before crusting over, and are contagious through direct contact, particularly when active or blistering. Canker sores appear only inside the mouth, don't blister or crust the way cold sores do, and aren't contagious at all, since they're not caused by a virus. If a sore is on your outer lip and blistering, it's a cold sore; if it's inside your mouth without blistering, it's almost certainly a canker sore.

Canker sores typically cause a burning or tingling sensation before the sore becomes visible, followed by pain, particularly when eating acidic or spicy foods that irritate the open sore. They're generally round or oval with a well-defined red border and a white or yellowish center.

The exact cause isn't fully understood, but several factors are commonly associated with triggering them, including minor injury to the inside of the mouth, such as accidentally biting your cheek, certain acidic or spicy foods, stress, hormonal changes, and in some people, specific nutritional deficiencies, such as low vitamin B12, iron, or folate.

### Risk Factors

Some people are simply more prone to recurrent canker sores than others, sometimes running in families, suggesting a genetic component. A weakened immune system, certain digestive conditions, and high stress levels are also associated with more frequent or severe canker sore outbreaks in some individuals.

Most canker sores are diagnosed based on their characteristic appearance during a visual exam, without needing additional testing. If sores are unusually large, don't heal within the expected timeframe, or occur very frequently, a doctor or dentist may investigate further to rule out an underlying nutritional deficiency or other contributing condition.

### How to Heal a Canker Sore Fast

Over-the-counter topical treatments designed specifically for canker sores can help reduce pain and may support faster healing. Avoiding foods that irritate the sore, particularly acidic, spicy, or rough-textured foods, while it heals also helps reduce discomfort and prevent further irritation to the area.

### Does Salt Help a Canker Sore?

A warm saltwater rinse is a commonly used home remedy that can help keep the area clean and may provide some temporary relief, though it can also cause a brief stinging sensation on the open sore. It's a reasonable supportive measure rather than a cure on its own.

### Helpful At-Home Tips

Using a soft-bristled toothbrush to avoid further irritating the sore, avoiding tobacco and alcohol-based mouthwashes that can sting and irritate the area, and maintaining good overall oral hygiene while the sore heals all support a smoother recovery.

Most canker sores heal on their own within one to two weeks without leaving a scar. Larger or more severe canker sores can occasionally take longer, and sores that persist significantly beyond this typical window are worth having evaluated.

See a doctor or dentist if a sore is unusually large, if you develop several sores at once regularly, if sores aren't healing within the typical two-week window, if you have a fever alongside the sores, or if you're experiencing very frequent recurrent canker sores, since this pattern is sometimes worth investigating for an underlying nutritional or health factor contributing to the outbreaks.

Are canker sores contagious? No, canker sores are not caused by a virus and are not contagious, unlike cold sores, which are caused by the herpes simplex virus and can spread through direct contact.

What foods trigger canker sores? Acidic foods like citrus fruits and tomatoes, and spicy foods, are commonly reported triggers for some people, though triggers vary by individual, and not everyone who eats these foods develops canker sores from them.

Can stress really cause mouth sores? Yes, stress is a commonly reported trigger for canker sore outbreaks in many people, though the exact mechanism isn't fully understood. Managing stress alongside other known triggers can help some people reduce how often they experience outbreaks.

Why do I keep getting canker sores in the same spot? Recurring sores in the same location can sometimes result from a specific repeated irritation in that spot, such as a sharp edge on a filling or a habit of biting the same area of your cheek. If this pattern continues, it's worth having a dentist check for a physical cause that might be contributing.

Should I be worried about a mouth sore that won't heal? A sore that persists for several weeks without improving, especially if it's painless, is worth having evaluated by a dentist or doctor, since most canker sores heal within about two weeks, and a sore that doesn't follow this typical pattern deserves a closer look to rule out other causes.