Canker Sores: Causes, Relief, and the Overnight Remedy That Actually Works

I get canker sores quite often when I’m exhausted, getting my period, or fighting a cold and they hurt like crazy. Canker sores—those small, shallow ulcers that pop up inside the mouth—can feel like a big deal when you’re trying to eat, drink, or even talk. While they’re not contagious like cold sores, the discomfort they bring can be frustrating, especially when they linger for a week or more. Fortunately, there’s a tried-and-true method for soothing the pain and dramatically reducing inflammation overnight. 

What Are Canker Sores?

Canker sores, or aphthous ulcers, typically appear on the soft tissues inside your mouth—like the inside of your cheeks, lips, under the tongue, or along the gumline. They often start as a red bump or sore spot, then develop into a white or yellow ulcer with a red border. They can get extremely sore to the point of not being able to eat or chew without pain shooting through your lips. 

While the exact cause isn’t always clear, several common factors can trigger or worsen canker sores.

Common Causes of Canker Sores

• Stress and fatigue
• Minor mouth injuries (biting your cheek or lip, aggressive brushing)
• Food sensitivities (especially acidic foods like citrus, tomatoes, and vinegar)
• Vitamin deficiencies (B12, zinc, folate, iron)
• Hormonal changes (like your period)
• Allergic reactions to toothpaste ingredients (like sodium lauryl sulfate)
• Immune system issues or underlying health conditions

I usually get canker sores when I am fighting a cold or stressed out. They start off so tiny and feel like they won’t bother you then they progressively get worse and can be very painful. Last night it hurt so bad just to eat dinner and you can forget about eating salty snacks or spicy foods. The burning was so bad I had to start doing treatment right away. 

How to Avoid Making Canker Sores Worse

• Avoid spicy, acidic, and salty foods while healing
• Skip abrasive toothpaste—look for SLS-free formulas
• Use a soft-bristled toothbrush to prevent additional irritation
• Don’t poke or pick at the sore—this delays healing
• Stay hydrated and maintain a balanced diet to support immune health
• Manage stress with relaxation techniques or healthy sleep habits

The Best Overnight Canker Sore Relief Method (That Really Works)

After experimenting with multiple treatments, one simple two-step routine stands out for its ability to calm pain and reduce swelling overnight:

Step 1: Salt Water Rinses Throughout the Day

Salt water is a natural disinfectant that helps reduce bacteria in the mouth, dry out the sore, and promote healing.

How to do it:

• Mix 1/2 tsp of salt in 1/2 cup of warm water
• Swish for 30 seconds to 1 minute
• Spit it out—do not swallow
• Repeat 3–4 times a day, especially after eating

Step 2: Baking Soda Paste at Night

Baking soda (sodium bicarbonate) helps neutralize acids, reduce inflammation, and soothe irritated tissue.

How to make and use it:

• Mix a small amount of baking soda with just enough water to form a paste
• Use a clean finger or cotton swab to dab it directly on the sore
• Leave it on overnight (it may harden slightly)
• If you can’t get it to stay and swallow it that’s fine too, I usually do a couple applications before bed and hold my lip open to air dry it slightly, leave it until morning and only drink water during the night
• Wake up to a noticeably calmer, less painful canker sore

Why It Works

Salt cleanses the mouth and helps prevent infection, while baking soda reduces acidity and inflammation—two of the main sources of canker sore pain. Together, they create an ideal environment for the sore to heal faster and with less discomfort. This morning when I had gotten up the swelling was way down and the pain is much more manageable. It has turned an ugly yellow colour since it is healing but I am so happy I took the time to do the treatments yesterday because it took so much of the pain away. 

Final Tips

While canker sores usually go away on their own within 7–10 days, using this routine can speed up recovery and make the healing process far less miserable. If sores are very large, last more than two weeks, or keep coming back, consult a healthcare provider to rule out underlying conditions.

For most people, though, this gentle, natural approach is a game-changer—a simple combo that truly delivers overnight relief. If it keeps bothering you keep doing salt water rinses everyday until it’s gone and a dab of baking soda before bed and you will be glad you did.