Living and Wellness Is It a Cold Sore or a Canker Sore? What’s the Difference? By UPMC, April 23, 2018 A little irritation develops near or inside your mouth, and you start to wonder what’s wrong. It hurts a lot more than it should, considering the small size. It seems to last awhile, and you can’t figure out whether it’s a cold sore or canker sore. So, what exactly is the difference between a cold sore and a canker sore? Let’s dive in. Fortunately, it’s not too complicated. UPMC AnywhereCare gives you easy online access to health care providers. Learn more today. Cold Sore vs. Canker Sore What is a cold sore? Outside of the mouth is where you’ll find a cold sore, sometimes called a fever blister. It usually appears as one or several red, blistered areas on your lips. The blisters often will break open causing an open sore, or ulcer. Within a few days, a scab will form. Some areas of the mouth take longer to heal because they frequently stretch when you talk, eat, or yawn. What causes cold sores? What causes cold sores is the herpes simplex virus and, unfortunately, the sores are contagious when they’re open. That means the virus can be spread when sharing utensils, drinks, or towels, and by kissing. The herpes virus stays in your body and can cause cold sore outbreaks at any time. Often, they’re triggered by things such as extreme temperatures, exhaustion, stress, or a weakened immune system. When you feel a cold sore coming on, usually indicated by a tingling or itching on the affected area, consider anything out of the ordinary that you’ve been experiencing, as this could be your trigger. Once you figure out what your triggers are, you can try to avoid them. Use sunblock if a cold sore is caused by sun exposure or take a few minutes to relax if stress is a trigger for you. How to treat a cold sore While there’s no cure for cold sores, treatment can help to shorten the lifespan or weaken the severity. Some people start treatment when they first notice symptoms. A cold sore treatment is for symptom relief, and can include an antiviral topical ointment, oral antiviral medication, or over-the-counter topical anesthetic or anti-inflammation agent. Your first cold sore can take up to three weeks to heal, but later ones may disappear in a week or two. While there’s not usually a reason to go to the doctor for a cold sore, your doctor can test for the virus with a swab and culture and prescribe antiviral medication. What are canker sores? Canker sores are found on the inside of the mouth, including the lips, cheeks, and tongue. They’re small ulcers that could be caused by a thing such as: Food allergies A weakened immune system Stress Mouth injury (like biting your tongue or cheek) Some medicines Viruses/bacteria Irritation caused by orthodontic braces The sores usually have a red base and may be covered by a white or yellow layer. How to treat canker sores Canker sores aren’t contagious, and they are not easily visible to others. They can be painful, though. You might try an oral pain reliever since ointments are difficult to keep in place when the sore is inside your mouth. Keeping your mouth clean by brushing regularly can help, and anesthetic mouth rinse can help ease the pain too. Some people find it helpful to avoid spicy, acidic, or salty foods while it’s healing, which can take up to two weeks. There’s no reason to go to the doctor unless the sores return frequently or are large. So, what is the difference between canker sore versus cold sore? Location, location, location! Cold sores are usually on the edge of the lips, while canker sores are inside the mouth. Cold sores are contagious and can be treated with antiviral ointments and pain relievers, while canker sores require only pain relief. And both can last a few weeks. For more information on treating oral sores or to find a doctor, contact UPMC.