What even is a recurrent mouth ulcer?

Before we dive into why they keep coming back, let’s make sure we’re on the same page about what we’re talking about. A mouth ulcer is basically a small, open sore inside your mouth—on your cheeks, lips, tongue, or the roof of your mouth. They’re usually round or oval, with a white or yellowish center and a red ring around them. And man, do they hurt—especially when you eat something spicy, acidic, or hot, or even when you brush your teeth a little too hard. Now, a one-off ulcer every now and then? Totally normal. Most people get one every few months, usually from accidentally biting their cheek or eating something too sharp. But if you’re getting them more than 3 times a year, or if you have multiple ulcers at once that take weeks to heal? That’s what we call recurrent, and that’s when it’s time to start paying attention. These aren’t the same as cold sores, by the way—cold sores are caused by the herpes simplex virus, usually form on the outside of your lips, and are contagious. Recurrent mouth ulcers are inside the mouth, not contagious, and have totally different triggers.

Your immune system might be working against you

One of the biggest culprits behind recurring mouth ulcers is your immune system. But here’s the twist: it’s not that your immune system is weak—it’s that it’s out of balance. Think of your immune system like a security guard for your body. Its job is to fight off bad stuff like bacteria and viruses. But sometimes, it gets confused and starts attacking healthy cells instead—like the delicate lining of your mouth. That’s exactly what happens with recurrent ulcers. The lining of your mouth (called the oral mucosa) gets inflamed, and small sores form as a result. Experts aren’t 100% sure why this happens, but it’s linked to a condition called autoimmune reactivity, where your body’s defense system turns on itself. So why does this happen repeatedly? Well, certain things can trigger your immune system to act up. Stress, lack of sleep, being sick with a cold or flu, or even hormonal changes can all throw your immune system off balance, leading to another round of ulcers. It’s like your immune system is on edge—one little push, and it overreacts. You might notice that you get ulcers right after a busy work week, or when you’re dealing with a lot of stress at home. That’s your immune system sending you a message: slow down, because it’s struggling to keep up. And if you have other autoimmune conditions, like lupus or Crohn’s disease, you’re more likely to get recurrent ulcers too, since your immune system is already out of whack.

Stress and sleep (or lack thereof) are bigger triggers than you think

Let’s talk about stress—because let’s be honest, most of us are stressed out more often than we’d like to admit. And guess what? Your mouth is one of the first places that stress shows up. I’ve had so many patients tell me, “Every time I have a big deadline or a fight with my family, I get a mouth ulcer.” And it’s not a coincidence. When you’re stressed, your body produces cortisol, the “stress hormone.” Cortisol is great in small doses, but too much of it throws off your entire body—including your immune system and the health of your oral mucosa. Stress also makes you more likely to grind your teeth, bite your cheeks, or clench your jaw without even realizing it—all of which can cause tiny injuries that turn into ulcers. Then there’s sleep. If you’re pulling all-nighters, or if your sleep is restless and unrefreshing, your body doesn’t get the chance to repair itself. Your oral mucosa needs time to heal and regenerate, just like the rest of your body. When you’re sleep-deprived, that healing process slows down, making it easier for ulcers to form and harder for them to go away. It’s a vicious cycle: stress causes poor sleep, poor sleep weakens your body, and that leads to more ulcers, which cause more stress… and on it goes. The good news? Even small changes—like adding 30 minutes of sleep each night, or trying a 5-minute meditation before bed—can help break that cycle. You don’t have to overhaul your entire life; just little tweaks to manage stress and sleep better can make a huge difference in how often you get ulcers.