--- title: "Cold sore inside the lip or a canker sore? How to tell" description: "Cold sores are contagious; canker sores aren't. Where each one forms (inside the lip, on the gums, around the lips), how they look, and what helps." canonical: https://oralbench.com/cold-sore-or-canker-sore alternate_html: https://oralbench.com/cold-sore-or-canker-sore language: en-US last_updated: 2026-09-27 type: guia --- # Cold sore or canker sore: which one is it, and does it spread? 1. [Home](https://oralbench.com/) 2. [Mouth & gums](https://oralbench.com/oral-health) 3. Cold sore or canker sore: which one is it, and does it spread? They sound alike, they both hurt, and people mix them up all the time. The difference matters, though: one is a virus you can pass on and the other isn't. By **OralBench editorial team**Updated September 27, 2026 ![Cold sore or canker sore: which one is it, and does it spread?](https://oralbench.com/img/guia-cold-sore-or-canker-sore-640.webp) Short answer A cold sore (fever blister) comes from the herpes simplex virus and is very contagious; a canker sore isn't contagious at all. The National Institute of Dental and Craniofacial Research (NIDCR) says "the main way to tell the difference between a fever blister and a canker sore is by location": fever blisters form outside the mouth, around the border of the lips, and canker sores form inside it. MedlinePlus adds that when cold sores do show up inside the mouth, "they are usually on the gums or the roof of the mouth." So an open white or yellow sore with a red border on the inside of your lip fits a canker sore much better. Any sore on your lip or in your mouth that lasts more than two weeks needs a dentist or a doctor, NIDCR says. ## Cold sore vs. canker sore at a glance Question Cold sore (fever blister) Canker sore What causes it The herpes simplex virus, usually type 1 (HSV-1) No known cause. Possible triggers include a bite, stress, hormones, quitting smoking and low folic acid, iron or vitamin B12 Does it spread? Yes, it's "very contagious" No Where it shows up Outside the mouth, around the border of the lips. Inside the mouth, usually the gums or the roof of the mouth Only inside the mouth: the inside of the lips or cheeks, the gums, the tongue What it looks like "Patches of several small fluid-filled blisters" Usually a single round white or yellow sore with a red border Any warning first? Burning or tingling where the blisters will appear Sometimes burning or tingling before the sore appears Other symptoms In more severe cases, fever, fatigue or swollen lymph nodes Pain, especially when eating, drinking or talking How long it lasts Usually 1 to 2 weeks, says NIDCR; MedlinePlus says they "normally go away on their own in a few weeks" Usually 1 to 2 weeks Does it come back? It can. The virus "generally stays in the nerve cells" and can flare up again; sun can set it off It can. Frequent ones are a reason to see a doctor NIDCR (National Institute of Dental and Craniofacial Research, NIH), "Fever Blisters & Canker Sores" (last reviewed August 2026) and "Oral Cancer"; MedlinePlus (National Library of Medicine) health topics "Cold Sores", "Canker Sores" and "Oral Cancer". Every page read on September 27, 2026. ## The sore is inside your lip. Now what? Start with where it is. Per NIDCR, fever blisters sit outside the mouth, "generally around the border of the lips," while canker sores "occur inside the mouth." A sore on the soft inner lining of your lip, the inside of a cheek or the tongue is canker sore territory. Cold sores can appear inside the mouth, but MedlinePlus says they're usually on the gums or the roof of the mouth. Then look at its shape. A fever blister is a cluster of small fluid-filled blisters. A canker sore is usually one round sore, white or yellow, with a red border. Both can start with burning or tingling, so that alone won't settle it. A fever, tiredness or swollen lymph nodes point toward the virus: NIDCR lists them among the "more severe symptoms" of fever blisters. In young children, fever blisters "can cause loss of appetite, drooling, and fever that can last for several days." If symptoms are severe or keep coming back, NIDCR says to talk to your doctor or your child's pediatrician. ## What helps each one, and when to get it checked ### Cold sore: antivirals and pain relief A doctor can prescribe antiviral medicines, as creams or pills, if needed. MedlinePlus adds that "other medicines can help with the pain and discomfort of the sores." ### Cold sore: sun and sharing Sun can set off an outbreak, and NIDCR says sunscreen "may help reduce their frequency" if you get them often. While you have one, skip kissing and don't share utensils, cups or water bottles. ### Cold sore: keep it away from your eyes Don't touch the blister and then your eyes. NIDCR warns the infection can spread there, "which can cause blindness." ### Canker sore: go easy on it Skip hot, acidic and spicy food, and pick a mouthwash without alcohol. Our canker sore page covers pain relief, including the FDA's caution about numbing products and children. ### No permanent fix for either "There is no cure for cold sores," MedlinePlus says, though antiviral medicines "can also help to prevent cold sores in people who often get them." NIDCR says no known treatment stops either kind from coming back for good. Be wary of anything sold as a way to be rid of them forever. ### When a lip sore needs a look NIDCR: "See a doctor if your cold sores last longer than a few weeks, you have a high fever, or you notice eye irritation." For any sore, its oral cancer page is just as plain: "If you have any of these symptoms for more than two weeks, see a dentist or a doctor," and the first symptom it lists is "a sore, irritation, lump or thick patch in your mouth, lip, or throat." MedlinePlus lists "a lip or mouth sore that won't heal" among the symptoms of oral cancer. ## Tooth supplements and lip sores None of the 12 supplements reviewed on this site is sold for cold sores, and nothing we recorded from their pages mentions herpes. Three of them, GumAktiv, DentiCore and OxyDental, come with bonus material that talks about canker sores and ulcers. That's a different problem from a cold sore, with a different cause. So if what you've got is a cluster of blisters on your lip, none of these products is even aimed at it. If it's a canker sore, our canker sore page sets those bonus promises against the nutrients NIDCR actually links to canker sores. ## Frequently asked questions **Can you get a cold sore inside your lip?** It's not the usual place. NIDCR says fever blisters form outside the mouth around the lips, and MedlinePlus says that when cold sores are inside the mouth, they're usually on the gums or the roof of the mouth. A sore on the inner lip fits the canker sore description better. **What causes an ulcer on the lip?** An open sore on the inside of the lip fits the canker sore description. Those have no known cause, though a bite, stress, hormones or low folic acid, iron or vitamin B12 may trigger one. Blisters on the outside of the lip point to a cold sore, caused by the herpes simplex virus. Whatever the cause, NIDCR says a sore on your lip or in your mouth that lasts more than two weeks needs a dentist or a doctor. **What is the treatment for a lip ulcer?** It depends on which one it is. For a cold sore, a doctor can prescribe an antiviral cream or pill if needed. A canker sore usually goes away on its own; our canker sore page covers pain relief. Either way, a sore that lasts more than two weeks needs a dentist or a doctor, NIDCR says. **Is a fever blister the same as a cold sore?** Yes. NIDCR says fever blisters are "also known as cold sores or herpes labialis." **Are canker sores contagious?** No. Fever blisters are "very contagious," NIDCR says, but canker sores are not. **Can a supplement get rid of cold sores?** Not one of the supplements reviewed here is sold for them. MedlinePlus says "there is no cure for cold sores"; antiviral medicines from a doctor and sun protection are what the sources suggest. ## Related pages Mouth & gums ### [Canker sores: what sets them off and what eases them](https://oralbench.com/canker-sores) 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. 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. 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