Most canker sores are small, heal on their own within two weeks, and respond well to simple home treatments that reduce pain while your body does the repair work. About 80% of canker sores fall into the “minor” category, measuring less than 5 mm across. The goal is to manage pain, avoid irritating the sore further, and speed healing where you can.
Rinses That Actually Help
A saltwater or baking soda rinse is the simplest and most reliable first step. Mix 1 teaspoon of table salt and 1 teaspoon of baking soda into 4 cups of warm water. Swish a mouthful gently over the sore for 30 seconds, then spit. You can repeat this several times a day, especially after meals when food particles can irritate the ulcer. The solution helps neutralize acids in your mouth and creates a cleaner environment for healing.
Hydrogen peroxide rinses (diluted to half strength with water) are another option. These work as a mild antiseptic and can help keep the sore clean, though they’ll sting briefly on contact.
Over-the-Counter Pain Relief
If the sore is making it hard to eat or talk, a topical numbing gel with benzocaine (sold as Orajel or Anbesol) can take the edge off quickly. You apply a small amount directly to the ulcer, and it temporarily blocks pain signals from that spot. The relief is real but short-lived, usually lasting 15 to 30 minutes, so it’s most useful right before meals.
Protective pastes that coat the sore and shield it from friction can also help. Look for products designed to form a barrier over mouth ulcers. These stick to the wet tissue inside your mouth and reduce the irritation you get from chewing, brushing, or acidic foods rubbing against the open sore.
What to Avoid While It Heals
Certain foods and habits will make a canker sore significantly more painful and can slow healing. Acidic foods like citrus fruits, tomatoes, and vinegar-based dressings are the biggest offenders. Spicy foods, salty chips, and anything with rough or sharp edges (like crusty bread or tortilla chips) can physically scrape the ulcer and reopen it.
Your toothpaste may also be a factor. Many toothpastes contain sodium lauryl sulfate (SLS), a foaming agent that can irritate mouth tissue. If you get canker sores frequently, switching to an SLS-free toothpaste is a low-risk change worth trying. Brush gently around the sore with a soft-bristled brush rather than avoiding the area entirely, since keeping your mouth clean supports healing.
Prescription Options for Severe Sores
For canker sores that are unusually large or painful, a doctor or dentist can prescribe a topical steroid to reduce inflammation. These come as gels or pastes you apply directly to the sore, and they work by calming the immune response that drives the swelling and pain. They’re most effective when applied early, as soon as you notice the sore forming.
Another clinical option is chemical cauterization with silver nitrate. A provider applies a silver nitrate stick directly to the ulcer, which destroys the nerve endings on the surface and creates a seal over the sore. Studies show significant pain reduction in the days following the procedure compared to leaving the sore untreated. It sounds aggressive, but the application takes seconds and many patients feel immediate relief.
When Canker Sores Keep Coming Back
Occasional canker sores are common and not a sign of anything serious. But if you’re getting them repeatedly, nutritional deficiencies are one of the most well-supported explanations. Low levels of vitamin B12, folate, and iron are all linked to recurrent outbreaks. Patients with low folate levels tend to get more frequent and more severe sores compared to those with normal levels, likely because folate plays a direct role in how cells repair damaged tissue.
Vitamin C deficiency is another contributor. Low vitamin C delays wound healing throughout the body, and in the mouth it shows up as slow-healing ulcers along with gum bleeding and fragile tissue. Stress is a well-known trigger too, though the mechanism is less clear. If you notice a pattern of sores appearing during stressful periods, that’s not coincidental.
A simple blood test can check for these deficiencies. If B12 or folate levels are low, supplementation often reduces how frequently sores appear. This is one of the more actionable things you can do if canker sores are a recurring problem rather than a one-time annoyance.
Canker Sores vs. Cold Sores
These are completely different conditions, but people mix them up constantly. The easiest way to tell them apart:
- Location: Canker sores form inside the mouth, on soft tissue like the inner cheeks, gums, or tongue. Cold sores appear on the outside of the mouth, typically on or around the lips.
- Appearance: A canker sore is usually a single round white or yellow sore with a red border. Cold sores are clusters of small, fluid-filled blisters.
- Cause: Cold sores are caused by herpes simplex virus type 1 and are contagious. Canker sores are not caused by a virus and are not contagious at all.
This distinction matters because the treatments are different. Antiviral medications work on cold sores but do nothing for canker sores, and vice versa.
The Three Types and What to Expect
Minor canker sores are the most common, making up roughly 80% of cases. They’re small (under 5 mm), oval or round, and heal within two weeks without leaving a scar. These are the ones most people are dealing with when they search for help.
Major canker sores are larger than 10 mm (about the width of a fingertip) and are a different experience entirely. They can last 5 to 10 weeks and may leave scarring. These are the sores that genuinely interfere with eating and drinking for extended periods and typically benefit from prescription treatment rather than just home care.
Herpetiform canker sores are rare and confusingly named, since they have no connection to the herpes virus. They appear as clusters of tiny ulcers, sometimes dozens at once, each only 2 to 3 mm across. Despite their small size, the sheer number of them can be extremely painful. They typically heal within one to two weeks.
Signs a Sore Needs Professional Attention
Any mouth ulcer that lasts three weeks or longer needs to be evaluated by a doctor or dentist. At that point, it’s no longer behaving like a typical canker sore, and other causes, including oral conditions that require different treatment, need to be ruled out. The same applies to sores larger than 1 cm, sores accompanied by high fever, or outbreaks so frequent or painful that they’re affecting your ability to eat normally.