--- title: "Canker sores: why they happen and how long they last" description: "A canker sore isn't contagious and usually goes away on its own in 1 to 2 weeks. What sets one off, what eases the pain, and when to see a doctor." canonical: https://oralbench.com/canker-sores alternate_html: https://oralbench.com/canker-sores language: en-US last_updated: 2026-09-27 type: guia --- # Canker sores: what sets them off and what eases them 1. [Home](https://oralbench.com/) 2. [Mouth & gums](https://oralbench.com/oral-health) 3. Canker sores: what sets them off and what eases them A canker sore is tiny and still manages to make every meal hurt. This page sets out what the National Institutes of Health says about them, and what the tooth supplements on this site do and don't bring to the problem. By **OralBench editorial team**Updated September 27, 2026 ![Canker sores: what sets them off and what eases them](https://oralbench.com/img/guia-canker-sores-640.webp) Short answer A canker sore, also called an aphthous ulcer, is a painful white or yellow sore with a red border that forms only inside the mouth, and it isn't contagious. The National Institute of Dental and Craniofacial Research (NIDCR) says canker sores and fever blisters typically "go away on their own in 1–2 weeks." Canker sores "do not have a known cause," but a bite, stress, hormonal changes, quitting smoking and a lack of folic acid, iron or vitamin B12 are possible triggers. See a doctor if they keep coming back or hurt enough to make eating or drinking difficult, and see a dentist or a doctor about any sore in your mouth that lasts more than two weeks. ## What a canker sore is, and where it forms NIDCR describes canker sores as "painful white or yellow sores that only form inside the mouth, usually on the insides of the cheeks or lips or on the tongue." Most of the time it's a single round sore with a red border. They can also turn up on the gums, and MedlinePlus adds two less obvious spots: "under your tongue, or in the back of your throat." The medical name is aphthous ulcer. They hurt most "when eating, drinking, or talking," and some people feel "a burning or tingling sensation in the area before the sore appears." They aren't contagious. That's the quickest way to tell them apart from cold sores (fever blisters), which come from the herpes simplex virus, spread easily and form on the outside of the mouth around the lips. The comparison has its own page, linked below. ## What sets one off ### A bite or a knock First on NIDCR's list of possible triggers is "an injury (such as an accidental cheek or lip bite)." NIDCR is careful to add that "reports vary" on all of them. ### Stress and hormones "Emotional stress" and "hormonal imbalances" are both on the list, and MedlinePlus mentions menstrual periods. Canker sores are most common during puberty and "occur less frequently after puberty." ### Quitting smoking An odd one, but NIDCR lists "smoking cessation" as a possible trigger. It's not a reason to keep smoking. ### Gaps in your diet, and other illnesses NIDCR names "nutritional deficiencies in folic acid, iron, or vitamin B12," and systemic diseases "such as inflammatory bowel disease or celiac disease." MedlinePlus adds food allergies and viral infections. ## Easing the pain while it runs its course Nothing makes a canker sore vanish. NIDCR says no known treatment gets rid of canker sores for good or stops them from coming back, and that treatment "is not usually required." What you can do is make the week hurt less. What to try What the source says Source Skip hot, acidic and spicy food These foods "can not only cause pain in existing ulcers but may also trigger new ulcers." NIDCR Numb it Over-the-counter gels that numb the pain. MedlinePlus: "Some ointments, creams or rinses may help with the pain." NIDCR; MedlinePlus Rinse with an antiseptic An over-the-counter antiseptic rinse "may help prevent infection of the sore." NIDCR Leave alcohol out of the rinse "Do not use mouthwashes that contain alcohol because they could irritate the sores." NIDCR Keep numbing products away from children Benzocaine, the numbing ingredient in several nonprescription mouth products, "should not be used for teething pain in children because they can be dangerous." It can lead to methemoglobinemia, "a serious, and sometimes fatal, condition." FDA NIDCR (National Institute of Dental and Craniofacial Research, NIH), "Fever Blisters & Canker Sores", last reviewed August 2026, and MedlinePlus (National Library of Medicine), "Canker Sores" health topic, and FDA, "Safely Soothing Teething Pain in Infants and Children" (content current as of June 26, 2024), all read on September 27, 2026. ## Canker sore promises on supplement pages, and the missing nutrients Three products reviewed on this site bring up canker sores, all of them in bonus material rather than on the label. GumAktiv's bonus guide takes on "canker sores, ulcers or candida" and says it will "get rid of them for good." DentiCore's promises to "get rid of canker sores, ulcers, dry mouth and candida." OxyDental's asks "Canker sores or ulcers?" and offers to "keep all these under control." Those are promises in a bonus guide, not facts about the tablet. Now set them against the nutrients NIDCR links to canker sores: "folic acid, iron, or vitamin B12." We went through the ingredient lists of all 12 products reviewed here. Not one lists any of the three. Even if one did, that wouldn't turn it into a canker sore remedy. NIDCR's advice for people who get them regularly is to "talk to your doctor about testing for certain diseases (e.g., celiac disease) or nutritional deficiencies." A test tells you whether you're actually short on something. A tooth supplement can't. ## When to have a sore looked at See a doctor, NIDCR says, "if you have frequently recurring canker sores or if the sores are severe enough to make eating or drinking difficult." Tests are rarely needed, it says, but may be done if sores "are severe, don't heal, or keep coming back." There's one more reason not to sit on a sore. NIDCR's oral cancer page lists "a sore, irritation, lump or thick patch in your mouth, lip, or throat" among its warning signs and says that if any of them lasts more than two weeks, you should see a dentist or a doctor. MedlinePlus lists "a lip or mouth sore that won't heal" among the symptoms of oral cancer. A canker sore that's still there after two weeks has outlasted the usual course, so get it checked. ## Frequently asked questions **What causes canker sores?** Nobody knows for sure: NIDCR says they "do not have a known cause." Possible triggers include a cheek or lip bite, emotional stress, hormonal changes, quitting smoking, some illnesses such as celiac disease, and a lack of folic acid, iron or vitamin B12. **How long does a canker sore last?** Typically 1 to 2 weeks, and it goes away on its own, according to NIDCR. Its oral cancer page says to see a dentist or a doctor about any sore in the mouth that lasts more than two weeks. **Why do I keep getting canker sores on my tongue?** The tongue is one of the usual spots, along with the inside of the cheeks and lips, and a bite is one possible trigger. If they keep coming back, NIDCR suggests asking your doctor about testing for certain diseases or nutritional deficiencies. **What over-the-counter medicine helps a canker sore?** NIDCR mentions over-the-counter gels that numb the pain and antiseptic rinses that may help prevent infection of the sore. Pick a mouthwash without alcohol, which can irritate it. And keep benzocaine products away from children: the FDA warns they "should not be used for teething pain in children." **Can a supplement stop canker sores?** None of the 12 tooth supplements reviewed here lists folic acid, iron or vitamin B12, the nutrients NIDCR ties to canker sores. If yours keep coming back, what NIDCR suggests is a talk with your doctor about testing, not a tooth supplement. **Is a canker sore the same as an aphthous ulcer?** Yes. NIDCR says canker sores are "also called aphthous ulcers." They're one kind of mouth ulcer; our mouth sores page covers the others, like cold sores and thrush. ## Related pages Mouth & gums ### [Cold sore or canker sore: which one is it, and does it spread?](https://oralbench.com/cold-sore-or-canker-sore) A cold sore (fever blister) comes from the herpes simplex virus and is very contagious; a canker sore isn't contagious at all. Read more Mouth & gums ### [Sores inside the mouth: what kind it is and when to worry](https://oralbench.com/mouth-sores) MedlinePlus lists cold sores, canker sores, thrush and leukoplakia among the common mouth problems, and dry mouth and cancer treatment can cause sores too. Read more Reviews ### [GumAktiv review: same strains as ProDentim, but it shows the dose](https://oralbench.com/gumaktiv) GumAktiv is a probiotic tablet you let dissolve in your mouth. Read more Updated September 27, 2026. [See our full method](https://oralbench.com/how-we-choose) --- ## OralBench - OralBench, published by Grupo Marfre Automação e Tecnologia (Contagem, Brazil) - Email: contact@oralbench.com - Home: https://oralbench.com/ - llms.txt: https://oralbench.com/llms.txt · llms-full.txt: https://oralbench.com/llms-full.txt · sitemap: https://oralbench.com/sitemap.xml