Canker Sores: Swords That Don’t Kill—but Sure Do Hurt

You know the feeling. A tiny sore starts brewing inside your mouth; before you know it, every sip of coffee or bite of a sandwich feels like you’re chewing glass. Canker sores—those small, painful ulcers that show up inside your cheeks, on your lips, or under your tongue—might be harmless, but they’re anything but forgettable. Let’s unpack what they are, what causes them, and how, as a dentist in Los Angeles, CA, I help patients find relief when one of these sneaky little swords shows up. 

What Are Canker Sores? 

Canker sores (also known as aphthous ulcers) are small, round, or oval lesions that form inside the mouth's soft tissues. Unlike cold sores, they’re not contagious and don’t appear on the outside of your lips. They often have a white or yellow center with a red halo—and yes, they hurt way more than their size suggests. 

They typically last 7 to 14 days, and while they usually go away on their own, they can make eating, drinking, and talking feel like a battle. 

What Causes Them? (It’s Complicated) 

The short answer? We don’t always know. But here are the most common triggers I’ve come to learn: 

• Stress - Your immune system can flare in response to anxiety or lack of sleep. 

• Minor mouth injuries - Accidentally biting your cheek or brushing too hard. 

• Acidic or spicy foods - Think citrus, tomatoes, vinegar, andhot sauces. 

• Nutritional deficiencies - Especially B12, iron, folate, or zinc. 

• Hormonal changes - Many women experience more canker sores during menstruation. 
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