Are Canker Sores an STD?

No — canker sores are not an STD, are not caused by any infection, and are not contagious. They're genuinely a different thing from an oral herpes cold sore, though the two get confused fairly often.

What canker sores actually are

Canker sores are small, shallow ulcers that form inside the mouth — on the inner cheek, tongue, or gums, not on the outer lip. Their exact cause isn't fully understood, but they're linked to factors like stress, minor mouth injury, certain food sensitivities, and hormonal changes, not any virus or bacteria. They typically heal on their own within one to two weeks.

How they differ from a cold sore

Cold sores (oral herpes, HSV-1) typically appear on or around the outer lip, start as small blisters rather than an ulcer, and are contagious through direct contact. Canker sores appear inside the mouth, start as an ulcer without a preceding blister phase, and can't be spread to another person. If you're unsure which one you're dealing with, location relative to the lip line is usually the clearest distinguishing detail.

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This page summarizes general, widely accepted information for educational purposes and isn't a substitute for advice from a healthcare provider about a specific situation.

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