Wellness Sexual Health Is It a Canker Sore or a Cold Sore? By Amanda Gardner Updated on April 19, 2024 Medically reviewed by Susan Bard, MD Medically reviewed by Susan Bard, MD Susan Bard, MD, is a board-certified general and procedural dermatologist with the American Board of Dermatology and a Fellow of the American College of Mohs Surgery. learn more In This Article View All In This Article How To Identify Cold Sores vs. Canker Sores Causes Diagnosis Treatment Tips A canker sore is a whitish or yellowish ulcer that appears inside the mouth. A cold sore (fever blister), in contrast, is caused by the virus herpes simplex virus 1 (HSV-1). HSV-1 lays dormant in your nerve cells after initial infection. If something activates HSV-1, blisters mostly appear outside your mouth, on or near your lips. A cold sore can sometimes develop inside your mouth, typically on the gums or roof of your mouth. Many people use the terms "canker sores" and "cold sores" interchangeably, but these painful mouth sores are different. Read on to learn how to tell the difference between a canker sore and a cold sore. Illustration by Paige McLaughlin for Health Skin Tag vs. Mole: Differences and Pictures How To Identify Cold Sores vs. Canker Sores Illustration by Paige McLaughlin for Health One of the main differences between canker sores and cold stores is the location. Canker sores only appear inside your mouth, while cold sores typically appear on the outside. Some of the main differences between canker sores and cold sores include: Canker Sores Cold Sores Are painful ulcers that may appear in clusters Are painful fluid-filled ulcers Are small in size (i.e., one-third of an inch in diameter) Crusts overs and scabs Are white or yellow with a red border and then become gray as they heal May cause itching or tingling before the blister develops Might cause burning or tingling before the ulcer appears Might occur with swollen glands, fever, and fatigue Only appear inside the mouth, on the insides of your cheeks, lips, and on your tongue Mostly appear on the outside of your mouth; sometimes appear inside the mouth, on the gums or roof of your mouth Canker Sores Canker sores (aphthous ulcers) appear as open sores on the inside of your mouth, usually on the inner parts of your cheeks, lips, or on your tongue. You likely will not find canker sores on the gums, but they may appear at the very base of your gums. Some people notice burning or tingling in their mouth before the ulcer forms. Canker sores, which often appear in clusters, are usually: Small (i.e., one-third of an inch in diameter)PainfulSmall bumps inside your mouth that burst after one to two daysWhitish or yellowish with a red border and then become gray as they heal Cold Sores MD SHAFIQUL ISLAM / Getty Images Cold sores (fever blisters) appear outside your mouth, often on the corner of your lip. They can also develop in your nose or eye. Symptoms include: Blisters that break quickly, leak fluid, and then crust and scab over Fatigue Fever Itching or tingling in the area up to one day before the ulcer appears Pain Swollen glands Causes Viruses cause cold sores, which are extremely contagious. Canker sores, on the other hand, are not contagious. It's unclear what exactly causes canker sores, but several things may increase your risk. Canker Sores No one knows what exactly causes or triggers canker sores, but they are not contagious. Risk factors may include: Food allergies Hormone changes and menstrual periods Nutritional deficiency (e.g., low folic acid, iron, or vitamin B12) Physical injury Smoking Stress Viral infection Cold Sores The virus HSV-1 causes cold sores. HSV-1, which is very contagious and common, does not go away once you get it. The virus travels up a nerve after the initial infection, where it stays out of sight until something triggers it. HSV-1 will then migrate down the nerve to the mouth, manifesting as a blister. Cold sore triggers can include: Dry, cracked lips Hot and cold temperatures Menstrual periods Other infections Stress Sun exposure Diagnosis A healthcare provider can typically tell the difference between a canker sore and a cold sore by examining the ulcer. See a healthcare provider if you have canker sores that make it hard to eat or drink or last longer than two weeks. They may administer diagnostic tests to check for allergies and herpes infection if you frequently get canker sores. Canker sores are also sometimes a sign of an underlying health problem like celiac disease. This autoimmune disorder, triggered by gluten (a protein in grains like barley, rye, and wheat), causes damage to the small intestine. You typically do not need to see a healthcare provider for cold sores. These blisters are generally not harmful unless you have a weak immune system from cancer treatment or another health condition like HIV/AIDS. In those cases, you may require more aggressive treatment, such as a long-term oral antiviral like acyclovir. Treatment Canker sores tend to last a little longer than cold sores. Most canker sores go away within one to three weeks. Cold sores, in contrast, go away within one to two weeks. Both mouth ulcers are typically harmless unless you have an underlying health condition. Canker Sore Canker sores mostly go away on their own. You can use an over-the-counter (OTC) pain reliever to alleviate discomfort, usually lasting seven or 10 days. Other ways to treat a canker sore include: Medications: A healthcare provider might prescribe chlorhexidine mouthwash or an oral or topical corticosteroid in severe cases. Gastric acid-reducing drugs sometimes treat pain. Milk of Magnesia (magnesium hydroxide): Try rinsing your mouth with a 50/50 mix of Milk of Magnesia and liquid Benadryl. Swish the mixture in your mouth for at least one minute. You may also apply a 50/50 mix of hydrogen peroxide and water and then a dab of Milk of Magnesia to the canker sore. Repeat three to four times per day. Mouth rinses: These include saltwater and OTC mouthwashes that do not contain alcohol. Cold Sore Most cold sores go away on their own within one to two weeks. You can treat a cold sore at home by applying a cold compress to the blisters or taking an OTC pain reliever. Topical antiviral creams or ointments may lessen pain and quicken healing if applied at the start of an outbreak. Cold sores can spread to other body parts, so it's important to avoid touching them. Wash your hands if you accidentally touch a cold sore. Make sure you do not touch any other part of your body, especially the eyes. Do not scratch or pick at the blisters, which might cause an infection. Tips Canker sores and cold sores are both painful ulcers that can be bothersome, especially when eating. You can take steps to avoid both canker sores and cold sores, especially if you know what triggers them. You can prevent canker sores by: Brushing your teeth twice per day and flossing dailyScheduling regular dental check-upsTalking to a healthcare provider about possible food allergies, which might trigger canker sores Cold sores are contagious and spread easily. You can prevent cold sores by: Avoiding triggers if possible (e.g., reducing stress or putting zinc sunscreen on your lips before going outside) Not kissing others until the blisters heal completely Not sharing straws and lip products or drinking from the same glass as others Washing your hands regularly, especially before you touch your eyes Scalp Psoriasis vs. Dandruff: How To Tell the Difference A Quick Review Both canker and cold sores are common but have different causes, symptoms, and treatments. The exact cause of canker sores is unknown, but HSV-1 causes cold sores. These mouth ulcers can be painful, and both typically go away on their own. If you have regular or prolonged canker sores, contact a healthcare provider. They can rule out any underlying health problems that may be the cause. Ask a healthcare provider about oral antiviral treatments if you have cold sores and a weak immune system. Was this page helpful? Thanks for your feedback! Tell us why! Other Submit 8 Sources Health.com uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. MedlinePlus. Canker sores. MedlinePlus. Cold sores. National Institute of Dental and Craniofacial Research. Fever blisters & canker sores. Nemours TeensHealth. Canker sores. Cold sores: Overview. Institute for Quality and Efficiency in Health Care (IQWiG); 2018. American Academy of Family Physicians. Canker sores. Nemours TeensHealth. Cold sores (HSV-1). National Institute of Diabetes and Digestive and Kidney Diseases. Dental enamel defects & celiac disease. Related Articles What Is Stomatitis? How Do I Know if I Have Herpes or Another Condition? Herpes Simplex Virus 1 vs. Herpes Simplex Virus 2—Understanding the Difference Can You Get an STI From Kissing? Here's What You Should Know Signs and Symptoms of Herpes Signs and Symptoms of Genital Herpes Dating With Herpes: How To Tell Your Partner Signs and Symptoms of Syphilis How Is a Cold Sore Treated? Can You Die From Herpes? What Is HIV Rash? Signs and Symptoms of Cold Sores Why Herpes Can Cause Repeated Outbreaks—and What To Do 4 Things That Can Make Your Vagina Feel Sore After Sex What Is Syphilis? Signs and Symptoms of Gonorrhea Newsletter Sign Up By clicking “Accept All Cookies”, you agree to the storing of cookies on your device to enhance site navigation, analyze site usage, and assist in our marketing efforts. Cookies Settings Accept All Cookies