Article by Mark Burheene

Here’s what they don’t tell you:

A 1977 study found that zinc supplementation reduced canker sore recurrence by 50% to 100% in patients with low zinc levels.

Yet somehow, decades later, most people suffering with recurrent canker sores have never even heard of this research. They’ve never had their zinc levels tested. They don’t know that a simple mineral deficiency could be at the root of years of pain.

If you get canker sores, you know how painful they are. They interrupt your meals, make talking uncomfortable, and stick around for 1-2 weeks at a time.

Most people try to numb the pain or just wait it out—without ever asking why it keeps happening.

Unlike cold sores (which are viral and contagious), canker sores are autoimmune. 

Think of them as your immune system waving a red flag, telling you something is off.

I’ve always told my patients: cankers can often be something you get when you’re run down. And if they keep coming back, there’s a root cause that needs addressing.

So let’s dig into what’s really causing them…

1. Zinc Deficiency: The Missing Piece

So why does zinc work?

Zinc is essential for immune function, wound healing, and cell proliferation. It supports collagen synthesis and has powerful anti-inflammatory properties. When you’re deficient, your mouth simply can’t heal the way it should.

If you’re getting 3+ canker sores a year, zinc deficiency should be on your radar.

Not all zinc supplements are created equal. Avoid zinc oxide, which has poor absorption. I use zinc picolinate (link to the one I take).

2. Your Oral Microbiome and Biofilm Are Depleted

Canker sores that appear often and heal slowly are a sign of a depleted biofilm. 

Without a healthy biofilm, your mouth’s immune barrier is compromised. You’re operating without one of your body’s core defenses.

Signs your biofilm might be depleted:

• Canker sores that heal slowly
• Bleeding gums, even with gentle brushing
• Dry mouth when you wake up
• Bad breath that doesn’t go away

One of the signs of low magnesium is canker sores on the tongue and inside the cheeks. Magnesium stabilizes beneficial bacteria and strengthens the biofilm matrix. Without it, the whole structure becomes unstable.

Most adults don’t hit the 500-600 mg of magnesium per day that supports optimal health. 

I’ve written about this extensively in past newsletters, but the takeaway is this: if your magnesium is low, your biofilm can’t stabilize. And that means more inflammation, more bleeding gums, and yes—more canker sores. (Link to the one I take.)

3. SLS in Your Toothpaste Is Stripping Your Mouth

I could always tell when my patients were using a toothpaste with SLS in it because of the sloughing of cheek cells on my intraoral mirror. It’s one of the most recognizable conditions in the mouth.

SLS—sodium lauryl sulfate—is a foaming agent that gives you that bubbly feeling when you brush. It makes you feel like your mouth is cleaner.

But what it’s actually doing is stripping away the protective mucosa layer inside your mouth, leaving your tissues vulnerable and prone to canker sores.

Multiple studies have linked SLS to increased canker sore frequency.

The cleaning solution I use on our garage floor is 50% SLS. And this is the ingredient most people are putting in their mouth twice a day.

For decades, I’ve been telling patients to go SLS-free. But when nano-hydroxyapatite came to the US market, there were NO SLS-free options that included it.

It felt like I was asking people to make a compromise: either get the remineralization benefits of nano-HAP, or avoid SLS. But toothpaste shouldn’t be a compromise.

That’s a big part of why I co-founded Fygg—so people could finally have both. No SLS, nano-hydroxyapatite, and full transparency about every ingredient.

But whether you use Fygg or another SLS-free brand, this is non-negotiable if you’re dealing with canker sores: ditch the SLS.

And watch out—manufacturers hide SLS under different names.

4. The Tortilla Chip Factor

So many people don’t realize that mechanical trauma is one of the most common causes of canker sores.

Tortilla chips. Crackers. Pretzels. Sharp edges on Invisalign aligners. A rough spot on your night guard. Even a sharp edge on your own tooth from grinding.

If your canker sore appears in the exact same spot each time, see your dentist. We can identify and smooth the sharp area—it’s an easy fix that people overlook for years.

I’ve seen instances where a sharp edge of a tooth (created by grinding) will cause a canker sore in the exact same location on the tongue or cheek every single time. Once we smooth it down, the problem disappears.

5. Stress, Poor Sleep, and Accidentally Biting Yourself

Stress can lead to bruxism (teeth grinding), which creates jaw tension, which makes you more likely to accidentally bite your cheek or tongue.

Poor sleep leads to muscle spasms and involuntary jaw movements. When you’re run down, stressed, and not sleeping well, your body’s coordination is off.

Multiple studies show that stress increases bruxism and involuntary facial muscle contractions. You’re more likely to bite yourself, and when you do, your depleted immune system can’t heal it as quickly. It’s a perfect storm.

Other factors that increase canker sores:

• Alcohol consumption (patients often balk at this one, but it’s real—you don’t have to quit, but you can titrate to find your threshold)
• Hormonal changes (menstrual cycle, menopause)
• Not getting enough sleep (I don’t mean 8 hours—I mean QUALITY sleep that doesn’t have tossing and turning, drooling on your pillow, twisted bed sheets, snoring and mouth breathing. Ask your dentist for a sleep apnea screening!) 

What to Do Right Now

Step 1: Start a Zinc Protocol

For active canker sores: Consider a zinc lozenges (let them dissolve against the sore 3-4 times a day). This provides a local anti-inflammatory effect and helps speed healing.

For prevention: Daily zinc supplementation: 15-25 mg per day is generally safe for adults without testing. Take it with food to prevent stomach upset. (This is the one in my vitamin cabinet.)

Important: This newsletter is for educational purposes only, so please talk to your doctor. The upper limit is 40 mg per day—don’t exceed this without medical supervision. And if you’re supplementing zinc long-term, make sure you’re also getting copper, as zinc can deplete copper levels.

Some food sources of zinc:

• Oysters (the richest source)
• Beef, lamb
• Pumpkin seeds
• Chickpeas, lentils
• Cashews, almonds (moderate to low)

Should you test first?

If you want to supplement 15-25 mg per day of zinc for prevention, you don’t necessarily need to test first—that’s within the safe range for most people. 

BUT—if you’re getting 3+ canker sores per year and want to know if zinc deficiency is truly YOUR issue, testing your serum zinc levels makes sense. 

The study I reference above showed people with low zinc (below 110 mcg/dL) got the most dramatic results—100% of them improved.

This is where working with a functional dentist comes in handy. They understand the oral-systemic connection and will actually dig into nutritional deficiencies rather than just handing you a steroid cream.

You can find a functional dentist in your area through our Functional Dentist Directory.

Step 2: Switch to a SLS-Free, Fluoride-Free Toothpaste Immediately

Even if you don’t get canker sores, I recommend this for everyone.

SLS is a detergent which emulsifies the biofilm on the oral mucosa. Fluoride can predispose us to canker sores as well.

Whether you use my toothpaste Fygg (code ATD15 for 15% off) or another SLS-free brand, make the switch this week.

Check your labels carefully—remember that SLS hides under multiple names.

Step 3: Restore Your Oral Microbiome

• Take an oral probiotic with Streptococcus salivarius (this is the one I take because it’s actually effective and formulated by oral microbiome scientists)
• Support your biofilm with magnesium
• Avoid essential oil mouthwashes, alcohol-based rinses, and Listerine—these strip your biofilm and make the problem worse. If you can’t give up the rinse, swish with coconut MCT oil—so great for the oral microbiome! 

Step 4: For Active Sores—Super Saturated Salt Rinse

This is free, and it works.

Mix Himalayan or Dead Sea salt in warm water. Make it SUPER saturated—more salt than you think. The way you know it’s super saturated is you keep stirring salt in until it no longer dissolves. A lot of people throw a tablespoon or two in there and it’s not even close. Keep going until it NO LONGER dissolves—this is key in order for this to work. 

Rinse for 5 minutes, four times a day.

This may burn a little at first, but it speeds up the new skin layer of the ulcerated area because salt stimulates the closing of the aphthous ulcer. Salt increases blood flow to the affected area and contracts the tissues, accelerating wound healing.

It also has a mild calming effect (after that initial burn).

Step 5: Address Mechanical Trauma

• See your dentist to smooth any sharp spots on your teeth
• Check your night guard, retainers, or Invisalign aligners for rough edges
• Use a soft-bristled toothbrush
• Eat carefully—slow down, chew mindfully, and avoid sharp foods when you have an active sore

Step 6: Manage Stress and Sleep

• Get 8 hours of sleep minimum
• Practice stress reduction (meditation, breathwork, exercise)
• If you grind your teeth, get fitted for a custom night guard

If you mouth breathe, this is huge: Mouth breathing dries out the oral mucosa, making it more likely to “ulcerate” aka get a canker sore. Try mouth tape and work with a myofunctional therapist to restore nasal breathing.

Step 7: Keep a Canker Sore Diary

Track when sores appear, what you ate, your stress levels, sleep quality, and (for women) where you are in your hormonal cycle. Look for patterns.

You can’t fix what you don’t track.

What NOT to Do

Avoid these common mistakes:

 Hydrogen peroxide – There’s no bacteria to kill with a canker sore. You’re just irritating it further.

 Listerine or antiseptic mouthwashes – These strip your biofilm and make the problem worse.

 Essential oils – Even the “natural” kinds burn and irritate canker sores.

 Canker sore covers – Every time I’ve seen these used, they prolong healing and increase pain.

 Just treating the symptom without finding the root cause – This is the biggest mistake of all.

Quick clarification: Canker sores are NOT the same as cold sores. Cold sores are viral, contagious, and appear outside the mouth (usually on the lips). Canker sores appear inside the mouth and aren’t contagious.

I hope this all helps. What topic would you like me to cover next time?

Mark