Overview
Both fever blisters and canker sores are common across all ages and can be painful. However, they are separate conditions with different causes. Read further to learn how to tell them apart and find out which treatments might help ease the pain.
Fever Blisters (also known as cold sores) are painful fluid-filled sores that form on the outside of the mouth around the lips. Fever blisters are very contagious.
Canker Sores are painful white or yellow sores that only form inside the mouth, usually on the insides of the cheeks or lips or on the tongue. Canker sores (also called aphthous ulcers) are not contagious.
Causes
Fever Blisters are caused by an infection with the herpes simplex virus, usually type 1, or HSV-1. It is estimated that nearly 90 percent of U.S. adults have been infected with the virus, although many people with the infection do not ever show symptoms. The virus generally resides in the nerve cells where it may periodically reactivate, traveling to the skin and causing recurring fever blisters.
Canker Sores do not have a known cause. They may be triggered by an injury, stress, smoking, or deficiencies in folic acid, iron, or vitamin B12.
Symptoms
Symptoms of fever blisters:
- Fluid-filled blisters on the outside of the mouth around the lips.
- Burning or tingling sensation at the site where the blisters will appear.
- And sometimes, fever, fatigue, or swelling of the lymph nodes, similar to other viral infections.
Symptoms of canker sores:
- A round white or yellow sore with a red border inside the mouth, usually on the inside of the lips or cheeks or on the tongue.
- A burning or tingling sensation may occur in the mouth prior to the formation of the sore.
Diagnosis
The main way to tell the difference between a fever blister and a canker sore is by location. Fever blisters occur outside the mouth, generally around the border of the lips. Canker sores occur inside the mouth.
They also differ in appearance: Fever blisters are patches of several small fluid-filled blisters, while canker sores are usually single round white or yellow sores with a red border.
Treatment
Typically, both types of sores go away on their own and treatment is not usually required. There is no known treatment that can permanently cure fever blisters or canker sores and prevent them from recurring. Treatment focuses on minimizing the pain and speeding recovery time.
Fever blisters can be treated with prescription antiviral medications either applied as topical creams or taken orally. See a doctor if your cold sores persist longer than a few weeks, you develop a high fever, or you notice eye irritation.
Canker Sores can be treated with over-the-counter (non-prescription) gels to numb the pain. Avoiding spicy or abrasive foods may also help. Rinsing the mouth with over-the-counter antiseptic medications may help prevent infection of the sore and speed healing.
See a doctor if you have frequently recurring canker sores or if the sores are severe enough to make eating or drinking difficult. If you have recurring canker sores as a result of a vitamin deficiency, treating the deficiency may reduce their frequency.
Helpful Tips
Both fever blisters and canker sores can have triggers that produce flare ups. Try to identify and then avoid triggers so your flare ups become less frequent.
Tips for Fever Blisters
- Sun exposure may sometimes trigger outbreaks of fever blisters. If you have recurring blisters, using sunscreen may help reduce their frequency.
- Fever blisters are contagious. Avoid kissing, sharing eating utensils, cups, water bottles, or other items if you are experiencing symptoms.
- Be aware that in young children, fever blisters can cause loss of appetite, drooling, and fever that can last for several days.
- Talk to your doctor or your child’s pediatrician if symptoms are severe or recur frequently.
Tips for Canker Sores
- If you regularly get canker sores, talk to your doctor about testing for food allergies, as allergic reactions can sometimes trigger canker sore outbreaks.
Additional Resources
- MedlinePlus (Fever Blisters)
Information about oral herpes (the infection that causes cold sores) from the NIH National Library of Medicine. - MedlinePlus (Canker Sores)
Information about canker sores from the NIH National Library of Medicine.
Cold sores: To know them is to loathe them.
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More than half of people in the U.S. have been infected with the virus that causes cold sores. Between 20 and 40% of them will experience the joy that is a cold sore.
If you’re one of them, odds are you know this pattern: A tingling or burning sensation on your lip. A day later, an oozy, fluid-filled blister on your mouth, always at the most inopportune time.
Family medicine physician Sarah Pickering Beers, MD, shares her advice for dealing with this sore spot.
Cold sores: common and contagious
Cold sores are common and mostly harmless. They’re caused by the herpes simplex virus, which spreads easily from person to person.
In some lucky people, the virus might cause a cold sore once or twice and never rear its head again. But for other people, they come back again and again, sometimes several times a year. And that gets old real fast.
“They tend to go away on their own in 10 to 14 days,” says Dr. Beers. “But that doesn’t make them any less annoying.”
Cold sore remedies
Two weeks might as well be an eternity when you have an oozy, scabby sore smack dab in the middle of your face. Here’s what you can do to ease the discomfort and send that cold on its way.
- Oral antiviral medications: “The most efficient way to get rid of cold sores is with oral antiviral medications,” Dr. Beers says. A doctor can prescribe these medications, which reduce pain and help the sore clear faster. But you have to start taking them within the first day or so that the cold sore develops, or they don’t do much to help, Dr. Beers says. If you’re one of the unlucky people who tends to get cold sore after cold sore, your doctor might be able to prescribe a daily antiviral to keep them at bay, Dr. Beers adds.
- Antiviral cream: If you can’t make it to a doctor for a prescription, over-the-counter antiviral creams can help knock back a cold sore. “These are slightly less effective than oral antivirals, but they do reduce the pain and duration of the sore,” Dr. Beers says. But like oral medications, you have to start using the cream ASAP for it to work.
How to treat cold sore pain
DIY remedies aren’t likely to make a cold sore disappear any faster. But there are things you can do to ease the pain while you’re waiting impatiently for it to heal.
- Numb the pain: Over-the-counter pain reliever creams such as lidocaine and benzocaine can numb the burning and ease the discomfort. These are often marketed for dental pain, so look for them in the dental section of the drug store.
- Moisturize: Keep your lip and mouth area moisturized to prevent the sore from drying out and peeling, Dr. Beers says. But if you use lip balm on an active sore, consider it contaminated. “Once you’ve used it on a cold sore, you should throw it away after the sore is better,” Dr. Beers says.
- Cool it: Using a simple cold compress, like ice or a cold, wet rag, can help reduce pain and redness.
- Hands off: It can take all your self-control not to play with a cold sore, but try to resist the temptation. “It’s instinct to pick at it and scrape the peeling skin, but you should let it heal itself,” Dr. Beers says.
Meanwhile, you don’t want to inflict these sores on others. Skip the make-out sessions until you’ve healed and wash your hands often.
While cold sores are annoying in adults, the virus can be life-threatening in a baby, so take care to steer clear, Dr. Beers advises: “As much as you might want to see your niece or nephew or grandbaby, please don’t shower them with kisses if you have an active cold sore.”