Those painful sores that pop up inside your mouth and make eating miserable—canker sores, or "aphthous ulcers" if you want the medical term—happen to about 20% of people at some point. They're incredibly annoying but usually not serious. Here's how to recognize what you have, treat it effectively, and prevent them from coming back.
Understanding Canker Sores: The Most Common Mouth Ulcer
Canker sores are small, painful ulcers that appear on the soft tissues inside your mouth—your cheek, lips, or under your tongue. They usually have a white or yellowish bottom with a red, inflamed border. The weird part is that we're still not entirely sure what causes them, though minor injuries (from aggressive brushing or accidentally biting your cheek), stress, certain foods, and nutritional deficiencies all seem to trigger them.
Most canker sores are small (less than 1 centimeter across), and they're just an annoyance. They hurt for a few days, then gradually heal over 1-2 weeks without scarring. Some people get them occasionally, others get them repeatedly. If you're someone who gets them frequently, there's usually a preventable cause you can address.
Large canker sores (bigger than 1 centimeter) are less common but more problematic. These are deeper, hurt more intensely, take much longer to heal (up to 6 weeks), and might leave a scar. If you're getting these repeatedly, you need to investigate why.
Is It a Canker Sore or Something Else?
Cold sores (herpes labialis) look similar but aren't the same thing. Cold sores usually appear on your lips and are contagious (canker sores aren't). They start with a tingle, then blister, then scab over. Cold sores are caused by a virus and need antiviral medication if you treat them early.
Traumatic ulcers come from obvious injuries—you bit your cheek, a sharp food cut your mouth, or a jagged tooth rubbed the area. These usually have a clear cause, and once you remove the irritation (fix the sharp tooth, stop biting that spot), they heal quickly.
Oral thrush is different too—it's white patches or areas that don't look like true ulcers. It's a yeast infection and needs antifungal treatment.
Treating Canker Sores: Steroids Work
For pain relief and faster healing, topical corticosteroid creams work. The most common is triamcinolone—you apply a tiny bit directly to the ulcer 2-3 times daily. It reduces pain pretty quickly (within hours) and accelerates healing compared to doing nothing.
If you have multiple ulcers or they're in hard-to-reach places, a dexamethasone rinse (swish it around your mouth) covers larger areas. The key is applying these treatments early. They work better if you start them right when the ulcer appears.
For pain management while it heals, benzocaine numbing gel (like Orajel) provides temporary relief that lasts about 15-30 minutes. You can reapply it as needed, especially before meals. It doesn't speed healing but makes eating less miserable.
OTC Approaches That Actually Help
Salt water rinses are old-school but effective. Mix half a teaspoon of salt in eight ounces of warm water and rinse 3-4 times daily. It's soothing, helps prevent secondary infection, and costs essentially nothing. Hydrogen peroxide rinses (3%) work similarly—they cleanse the area and help prevent bacteria from making it worse.
The topical anesthetics and oral gels at the drugstore provide comfort but don't actually heal the ulcer. They're worth using if you're in pain, but don't expect them to make the ulcer go away faster.
The Nutritional Connection: Worth Investigating
If you're getting canker sores repeatedly, consider nutritional deficiency. About 50% of people with frequent ulcers have a deficiency in vitamin B12, folate, iron, or zinc. If you're getting more than 4 canker sores per year, ask your doctor for blood work checking these nutrients.
If deficiency is found, supplementing usually reduces ulcer frequency within a couple of months. You might not need supplementation forever—sometimes addressing the deficiency is enough. But it's worth checking if you're having frequent episodes.
One Simple Switch: Toothpaste Matters
Here's something surprisingly practical: if you get canker sores frequently, switch to a toothpaste without sodium lauryl sulfate (SLS). That's the ingredient that makes toothpaste foamy. Research shows switching to SLS-free toothpaste reduces canker sore frequency by 40%.
Why? SLS apparently irritates mouth tissue, especially in people with sensitive mouths. If you're prone to ulcers, SLS-free toothpaste is an easy fix that costs maybe an extra dollar per tube. A lot of brands make SLS-free versions now.
When to Worry: Biopsy Red Flags
If an ulcer hangs around for more than 3 weeks without improvement, looks unusually deep, has weird irregular borders, or appeared in an unusual location, get your dentist to take a look. Most ulcers heal in 1-2 weeks, so something lingering is worth investigating.
Your dentist might do a biopsy (takes a tiny tissue sample for examination) if anything looks suspicious. This isn't because your dentist thinks you have cancer (you probably don't), but because persistent ulcers can occasionally be something other than a canker sore.
Avoiding Future Ulcers
Beyond SLS-free toothpaste, avoid triggers. For many people, spicy foods, acidic foods (citrus, tomatoes), or crunchy sharp foods (chips, hard candy) trigger ulcers. If you notice a pattern, avoid those foods.
Use a soft toothbrush and be gentle when brushing—aggressive scrubbing can cause traumatic ulcers. If you bite your cheek repeatedly, try chewing on the other side until you break the habit.
Some people notice stress triggers ulcers. If that's your pattern, stress management helps. Others notice they get ulcers after certain foods (peanuts, chocolate, gluten). If you see a pattern, eliminating that food prevents future sores.
Bottom Line
Most canker sores are just annoying minor problems that heal on their own. If they're painful, apply a corticosteroid cream or anesthetic to manage symptoms. If you get them repeatedly, switch to SLS-free toothpaste, look for nutritional deficiencies, and identify food or stress triggers. If you get large ulcers or anything that doesn't heal in 2-3 weeks, have your dentist check it. With the right approach, you can reduce how often they happen and manage them better when they do.
Related reading: Recovery After Tooth Extraction and Protective Mouth Guards: Preventing Dental.
Conclusion
Talk to your dentist about your specific situation and what approach works best for you. Most canker sores are just annoying minor problems that heal on their own. If they're painful, apply a corticosteroid cream or anesthetic to manage symptoms. If you get them repeatedly, switch to SLS-free toothpaste, look for nutritional deficiencies, and identify food or stress triggers.
> Key Takeaway: Those painful sores that pop up inside your mouth and make eating miserable—canker sores, or 'aphthous ulcers' if you want the medical term—happen to.