Sometimes it happens when you’re eating and, suddenly, you bite the side of your cheek. Or you notice a stinging and redness on your upper or lower lip and you know what’s coming: a cold sore. Or maybe you have a canker sore — one painful enough that it makes enjoying a meal difficult. You wouldn’t be alone.

Cold sores — also called fever blisters — are caused by herpes simplex virus 1. You might hear them called oral herpes, and they occur around and in the mouth. They’re contagious.

Unlike cold sores, canker sores, which occur mainly inside the mouth, aren't contagious. They develop on the tissues in the mouth or at the base of the gums, and they can be quite painful.

But whatever their type or origin, most of us have experienced painful sores on the mouth, lips, tongue, and inner cheek. And while they rarely call for a trip to the doctor, they can be embarrassing, especially if they are visible.

Here’s what you need to know and what to do about these mostly harmless lesions.

Causes and Risk Factors of Mouth Lesions

Sores on the tongue or inside the mouth may also be caused or exacerbated by other infections, inflammation, stress, or, very rarely, cancer. If the sore is deep, or if it gets irritated or infected, it may also bleed.

Some mouth sores and lesions may have more obvious causes, such as sharp or broken teeth or braces with protruding wires.

Gritting or gnashing your teeth, especially while sleeping, can cause tiny bites on the inside of your cheeks. Gum disease and inflammation can also cause bleeding in and around the gumline.

Biting your tongue or chewing your lips can cause pain, swelling, and even small cuts. Drinking hot liquids, smoking cigarettes and cigars, and consuming alcoholic beverages can also lead to mouth lesions, as can brushing or flossing too vigorously or using a hard toothbrush.

Cold sores, because they’re a form of herpes, are transmitted by oral-to-oral contact and through saliva, which means you can develop them through kissing or by sharing utensils with someone who has a cold sore. This type of herpes virus can also be transmitted to the genitals through oral-genital contact and cause genital herpes. (Herpes simplex virus 1 causes oral herpes and a different form of the virus — herpes simplex virus 2 — causes genital herpes.)

While cold sores are caused by a virus, the exact cause of canker sores is unknown. But there are several things than can trigger an outbreak. These include food allergies, stress, hormonal changes, vitamin deficiencies, or even spicy foods. Acidic fruits and vegetables may also trigger canker sores.

Often, people with recurrent canker sores have a family history of the disorder. They are also linked to rheumatologic conditions like lupus. (See below for other related conditions.)

How Are Mouth Lesions Diagnosed?

Your doctor or dentist can identify what kind of lesions or sores you have just by looking at your mouth. If you have recurrent, very large, or painful sores, you might need to undergo tests to make sure there’s not an underlying health problem. For cold sores, your doctor may test your blood for antibodies to herpes, yet this is not routinely done as the test results can be misleading.

Make sure to contact your doctor if you’re experiencing a fever.

Prognosis of Mouth Lesions

Treatment isn't typically needed for sores, which tend to clear up on their own in a week or two.

Treatment and Medication Options for Mouth Lesions

You can usually treat most common mouth sores or blisters yourself, at home, by taking a few simple steps or modifying your habits.

Medication Options

Nonsteroidal anti-inflammatory drugs (NSAIDs), like aspirin or ibuprofen, can help alleviate pain. Medicated lip balms, especially those formulated for herpes 1 and canker sores, can also help.

Depending on the type and size of the sore, or whether or not it is healing on its own, you may need antibiotics, an antiviral medication, an antiseptic mouthwash or a rinse containing the steroid dexamethasone to ease pain and swelling. Lidocaine is another pain-reducing option.

Occasionally, a procedure known as cautery may be necessary, where the tissues of your mouth are burned and then sealed up by chemicals or another instrument.

Alternative and Complementary Therapies

Baking soda rinses might help to alleviate pain. Applying ice, cold towels, or cooling ointments to afflicted areas may also soothe discomfort. As can applying small amounts of milk of magnesia on canker sores a few times a day.

Be sure to use a soft brush to brush your teeth. It’s thought that sodium lauryl sulfate, a common ingredient in toothpastes, could also trigger canker sores, so it might be a good idea to find a toothpaste without it if you have recurrent sores, and also discuss with your dentist.
More on Complementary Therapies

When Stress Triggers a Herpes Outbreak, These Complementary Therapies May Calm It Down

Prevention of Mouth Lesions

If you have cold sores, you should avoid should kissing people when you have an outbreak — indeed, avoiding close contact altogether. Make sure to steer clear of people who have weakened immune systems, like newborns or those undergoing cancer treatment, notes Penn Medicine.

It’s never a good idea to share lip balms, razors, toothbrushes, towels, or beverages, but it’s especially important to avoid doing so if you have a cold sore or feel one coming on. And while it may be tempting, try not to touch them. If you do, wash your hands.

When your lips are free and clear of sores, use a lip balm with sunscreen, as sunburn is another trigger for cold sores, per the Cleveland Clinic.

Research and Statistics: Who Has Mouth Lesions?

It’s been estimated that about 27 percent of Americans experience mouth lesions.
In the United States, the virus that causes cold sores (HSV-1) infects more than half the population by the time they’re in their twenties, according to the National Library of Medicine.According to the Centers for Disease Control and Prevention (CDC), women are more slightly likely to have HSV-1 than men (50.9 percent compared with 45.2 percent).
In 2016, according to a May 2020 article in the Bulletin of the World Health Organization, an estimated 3.7 billion people worldwide had an HSV-1 infection. That’s 66.6 percent of the world’s population of adults ages 0 to 49.

Related: Icky Mouth Mysteries Solved

Resources We Love

The American Dental Association’s Mouth Healthy website is a trustworthy and thorough source of information about dental hygiene.

Editorial Sources and Fact-Checking


  • Cold Sores vs. Canker Sores: What Are They and How Do I Get Rid of ‘Em? Penn Medicine. July 9, 2019.
  • Cold Sores. Cleveland Clinic. September 9, 2019.
  • Plewa M, Chatterjee K. Apthous Stomatitis. StatPearls. August 8, 2020.
  • Canker Sores. Mayo Clinic. April 3, 2018.
  • Cold Sores. MedlinePlus. September 29, 2020.
  • Shulman J, Beach MM, Rivera-Hidalgo F. The Prevalence of Oral Mucosal Lesions in U.S. Adults: Data From the Third National Health and Nutrition Examination Survey, 1988-1994. The Journal of the American Dental Association. September 2004.
  • McQuillan G, Kruszon-Moran D, Flagg E, Paulose-Ram R. Prevalence of Herpes Simplex Virus Type 1 and Type 2 in Persons Aged 14–49: United States, 2015–2016. Centers for Disease Control and Prevention. February 2018.
  • James C, Harfouche M, Welton N, et al. Herpes Simplex Virus: Global Infection Prevalence and Incidence Estimates, 2016. Bulletin of the World Health Organization. May 2020.
  • Behçet’s Disease. Cleveland Clinic. June 2, 2020.


  • Mouth Sores. MedlinePlus. August 12, 2020.
  • Hennessey B. Recurrent Aphthous Stomatitis. Merck Manual Consumer Version. June 2020.
  • Canker Sores. Cleveland Clinic. August 29, 2019.


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