Oral pH and Canker Sores: What Research Says (and What You Can Do About It)

If you get recurring canker sores, you have probably heard a dozen theories about triggers. One that actually shows up in the research is oral pH, basically how acidic or alkaline your saliva is.

This post pulls together what the studies suggest (including a solid 2017 paper), why acidity might matter biologically, and a few practical things you can try that are low drama and low risk.

The research: people with canker sores have more acidic saliva

One of the clearer data points comes from Foglio-Bonda et al. (2017). They measured salivary pH in 164 people: 84 with oral lesions (including aphthous ulcers) and 80 healthy controls. The result:

• Oral lesions group: average pH 6.69
• Healthy controls: average pH 6.96

That difference was statistically significant ((p < 0.001)). It looks small, but the pH scale is logarithmic, so it represents a real change in acidity.

An older study by Maurice et al. (1987) found a similar pattern and added an interesting detail: the pH drop appeared more pronounced at night than during the day. They also reported that, even after ulcers healed, some people stayed slightly more acidic than controls, which could help explain why outbreaks repeat for some of us.

Why would acidic saliva matter?

Your mouth lining does not love acid. When the local environment is more acidic, a few things can shift in ways that plausibly make ulcers easier to trigger or harder to calm down.

• Cell stress and damage

  • Oral cells have pH-sensitive mechanisms.
  • In lab work, prolonged exposure around pH ~5.5 to 6.0 can increase cell stress and cell death, depending on the model.

• Inflammation tends to rise

  • Acidic conditions can activate inflammatory pathways, including the NLRP3 inflammasome in some contexts, which increases pro-inflammatory signaling.

• The oral microbiome can shift

  • Research on recurrent aphthous stomatitis (RAS) finds differences in bacteria between people with ulcers and healthy controls, with shifts in Streptococcus species and other taxa (see BMC Oral Health, 2020).

None of this proves pH is the main cause. It does suggest acidity can be one part of the environment that makes the mouth more “ulcer-prone.”

What is a normal oral pH?

Healthy saliva usually sits around pH 6.7 to 7.4, with an average close to 7.0 (neutral). It also varies by location in the mouth. For example, Aframian et al. (2006) reported the palate as more alkaline and cheeks as more acidic on average.

One critical threshold people talk about is pH 5.5. Below that, enamel demineralization becomes more likely, and soft tissues generally do not enjoy the environment either.

Also, a quick “why the 6.69 vs 6.96 gap matters” point: a pH difference of 0.27 corresponds to about a (10^0.27 \approx 1.86) increase in hydrogen ion concentration. In plain language, that is roughly 1.9x more acidic, not a tiny change.

What pushes your mouth toward acidic?

Acidic foods and drinks

Many common beverages are strongly acidic. Reddy et al. (2015) tested 380 beverages and found a large fraction were highly erosive.

Common culprits include:

• sodas
• energy drinks
• sports drinks
• citrus juices
• vinegar-heavy foods
• wine
• coffee (mildly acidic)

Non-diet factors that matter too

• Dry mouth: less saliva means weaker buffering, slower recovery
• Mouth breathing: dries tissues and reduces buffering
• Acid reflux (GERD): gastric acid can reach the mouth in some cases
• Stress: can affect saliva flow and composition

What pushes your mouth toward alkaline (or at least, less acidic)?

• Water: neutral and helps dilute acids
• Dairy (especially cheese): often helps neutralize acids after eating
• Vegetables, especially leafy greens
• Some fruits: bananas and melons are often better tolerated than citrus

How your mouth recovers: the Stephan Curve

Dentistry uses the Stephan Curve to describe what happens after you eat or drink something sugary or acidic:

1. pH drops.
2. Over roughly 20 to 40 minutes, saliva buffers things back toward normal.

Two patterns make the “recovery” part fail:

• Sipping acidic drinks all day: you keep restarting the clock, so the mouth stays acidic for hours
• Dry mouth: buffering is weaker, so recovery is slower

Practical tips to keep pH more neutral (without getting weird about it)

Baking soda rinses

This is one of the more evidence-backed home approaches and is commonly recommended by major medical sites.

• Mix about 1 teaspoon baking soda in 1/2 cup warm water
• Swish 15 to 30 seconds, then spit
• Repeat a few times a day, especially after acidic foods

Time your acidic foods and drinks

Try to have acidic drinks with a meal rather than sipping for hours. Then switch back to water so your mouth can recover.

Do not brush immediately after acidic foods

Wait at least 30 minutes. Brushing while pH is low can increase enamel wear.

Rinse with plain water after acidic things

A quick water rinse can help dilute and clear acids.

Support saliva

• stay hydrated
• chew sugar-free gum (xylitol-based is a common choice) if it suits you

Watch for SLS if you are prone to ulcers

Sodium lauryl sulfate (SLS) is a known trigger for many people with recurrent canker sores. If you have not tried switching, see: SLS-Free Toothpaste for Canker Sores

Address reflux if it applies to you

If you have known GERD, or suspect silent reflux, treating it can sometimes improve oral symptoms too. This is a “talk to a clinician” item, not a DIY project.

The bottom line

Across studies, people with recurrent canker sores often show more acidic saliva than people who do not get them. pH is not the whole story (genetics, immune factors, stress, and nutrition all matter), but it is one of the few pieces you can influence without major downside.

Keeping your mouth closer to neutral pH will not guarantee you never get another canker sore, but it can remove one potential irritant from the pile.

Sources

1. Foglio-Bonda et al. (2017). “Salivary flow rate and pH in patients with oral pathologies.” European Review for Medical and Pharmacological Sciences. PubMed
2. Maurice et al. (1987). “Aetiology of recurrent aphthous ulcers.” Journal of Laryngology & Otology. PubMed
3. BMC Oral Health (2020). “Comparison of microbiomes in ulcerative and normal mucosa of recurrent aphthous stomatitis-affected patients.” Article
4. Aframian et al. (2006). “The distribution of oral mucosal pH values in healthy saliva secretors.” Oral Diseases. PubMed
5. Reddy et al. (2015). “The pH of beverages available to the American consumer.” Journal of the American Dental Association. Full text