TL;DR
Baking soda (sodium bicarbonate) is frequently recommended for canker sores, typically to "neutralize acid and promote healing." The problem: this rationale is based on a misunderstanding of what canker sores are. They're not caused by acid. They're immune-mediated lesions — the immune system attacking oral tissue. Neutralizing oral pH does nothing to stop that process. There's no published RCT showing baking soda reduces canker sore pain or healing time. It's mildly abrasive and can irritate already-damaged mucosa. Skip it.
Why People Think Baking Soda Works
The logic goes: canker sores hurt when you eat acidic food → acid must be causing the problem → baking soda is alkaline → neutralizing the acid will help.
Each step of that chain is wrong or incomplete.
Step 1: Acid does cause pain with canker sores — this part is true. Citrus, tomatoes, vinegar, and carbonated drinks all cause sharp, immediate pain when they contact an open ulcer. The sensation is real.
Step 2: Acid doesn't cause canker sores — the pain from acidic food is because acid contacts exposed nerve fibers in an already-open wound. Acid isn't creating the wound; it's irritating one that the immune system created. This is a critical distinction. See What Causes Canker Sores for the actual mechanism.
Step 3: Neutralizing acid doesn't address the cause — even if you perfectly buffered the oral pH with baking soda, you haven't touched the immune process producing the ulcer. The CD8+ T-cells attacking the oral epithelium don't care about pH.
This is the baking soda recommendation in a nutshell: a remedy for a cause that isn't the cause.
What the Evidence Actually Shows
No quality clinical trial has tested baking soda specifically for aphthous ulcers. The evidence base is: zero.
There is evidence for baking soda in adjacent oral health contexts — it's mildly effective against some oral bacteria, and it's used as a mild abrasive in toothpaste. But these don't translate to canker sore treatment:
- Bacterial load is not the cause of canker sores. Reducing oral bacteria doesn't change the immune attack driving the ulcer.
- Abrasiveness is actively counterproductive on an open ulcer. Baking soda paste applied to a canker sore can mechanically irritate tissue that's already raw.
Some people report temporary relief after applying baking soda paste. The most likely explanation: the paste physically coats the ulcer surface for a brief period, similar to (but less effective than) a purpose-built protective gel or patch. The coating provides transient relief; the baking soda itself is doing nothing therapeutic.
Baking Soda Rinse vs. Baking Soda Paste
There are two ways people use baking soda for canker sores:
Baking soda paste: Mixed with water to a thick consistency and applied directly to the ulcer. Mildly abrasive, can irritate damaged tissue. No healing evidence. Some brief coating effect.
Baking soda rinse: Dissolved in water and used as a mouthwash. Milder than the paste and less irritating. The mildly alkaline rinse is similar to salt water in its effects — mechanically clears debris, mildly adjusts oral pH. Like salt water, there's no RCT evidence for canker sore healing, but the rinse version is at least not actively abrasive.
If you're going to use baking soda at all, the rinse is less likely to irritate. But it's still doing essentially nothing for the ulcer.
What Baking Soda Is Actually Good For
To be fair to sodium bicarbonate: it does have legitimate oral health uses.
- Tooth whitening: Mildly effective as an abrasive. Many whitening toothpastes use it.
- Temporary pH buffering: Can briefly neutralize acidic conditions in the mouth, which is relevant to acid erosion of enamel.
- Mild antibacterial effect: Some evidence in dentistry for baking soda's effect on acid-producing bacteria involved in decay.
None of these translate to aphthous ulcer treatment. If you're dealing with canker sores, these properties are irrelevant.
What Actually Helps Instead
For pain while you have an active ulcer:
- Physical barrier patch (Canker Cover) — removes the constant food/saliva agitation that's the main source of pain, lasts 8–12 hours
- Benzocaine 20% gel (Orajel) — fast-acting anesthetic, 10–20 minutes
For prevention if you get frequent outbreaks:
- SLS-free toothpaste — switching away from sodium lauryl sulfate in toothpaste has one of the strongest evidence bases of any home intervention (64% reduction in one RCT)
For the full evidence-graded home remedy comparison, see Do Home Remedies for Canker Sores Actually Work?