Plus how you can soothe a cold sore the next time you get one.

By Lindsey Lanquist
May 20, 2021
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If you've ever discovered a painful blister on or around your lips, you've likely ended up with a couple questions. Like, what is this thing? And, how can I get rid of it? Often, these blisters are cold sores. And they're the result of a (very common) viral infection. To learn more about where these cold sores come from—and how you can treat them—we talked to a few experts.

What Is a Cold Sore?

A cold sore is a small, fluid-filled blister that forms on or around your mouth. You may find them on your lips, around your mouth, and inside your mouth. And sometimes, you'll find several clustered together. 

"A cold sore usually starts with a strange tingly feeling on your lip," says Noreen Galaria, MD, a board-certified dermatologist in Virginia. "This is soon followed by small bumps that will turn into painful, fluid-filled blisters." A few days after you spot a cold sore, it may blister and scab. And it will typically heal on its own within one to three weeks.

Cold sores are often called fever blisters, so you can use those terms interchangeably. That said, cold sores are not the same thing as canker sores, which are non-contagious small blisters that form inside your mouth.

Cold sores and canker sores also tend to look a little different. "Cold sores usually occur in a cluster," says Dr. Galaria. "This [clustering] is often a good hint that it is a cold sore, rather than a pimple or a canker sore."

cold-sores: woman covering mouth
Credit: Getty Images

What Causes Cold Sores?

Cold sores are caused by herpes simplex virus. Most are caused by herpes simplex virus type 1 (HSV-1), but some are caused by herpes simplex virus type 2 (HSV-2). 

Hearing the word "herpes" may leave you feeling a little worried. But rest assured knowing that herpes is an incredibly common virus. According to the American Academy of Dermatology (AAD), more than half of Americans between the ages of 14 and 49 carry herpes simplex virus. And many people who have HSV-1 have contracted it during childhood. (So while herpes is often classified as an STD, you might not have contracted it sexually.)

Since herpes simplex virus is a lifelong virus, you can never fully cure it. You might experience cold sores once or several times throughout your life, and some triggers can cause them to flare up. These include:

  • Stress
  • Illness 
  • Fatigue
  • Certain foods
  • Hormonal changes
  • Dental work or cosmetic surgeries
  • Injury (especially one near your mouth)
  • Infections
  • Allergic reactions
  • Excessive sun exposure

Are My Cold Sores Contagious?

Cold sores are caused by herpes simplex virus, and herpes is contagious. So yes, your cold sores are contagious. And you can spread them via kissing, oral sex, and other forms of skin-to-skin contact. 

"It is true that sharing drinks, lip gloss, or utensils with somebody who has a cold sore can cause you to contract it," says Dr. Galaria. "Generally, however, the greater the contact, the more likely you are to get a cold sore." In other words, you're much more likely to spread cold sores through skin-to-skin contact than you are to spread them through sharing drinks or utensils.

And technically, you could be contagious at any time. You're most likely to pass the virus on to someone else while you have an active cold sore outbreak. But since herpes is a lifelong virus, you can pass it on at any time—even when you don't have active cold sores. 

It's worth noting that while you're experiencing an oral herpes simplex virus infection, you can give someone else a genital herpes simplex virus infection. That's because both HSV-1 and HSV-2 can manifest as either an oral or a genital infection, depending on where someone has been exposed to the virus. 

This doesn't mean you have to worry about your cold sores spreading elsewhere on your body. Once you've contracted the virus orally, your body will build up antibodies to it. So that strain (either HSV-1 or HSV-2) won't spread anywhere else. (That said, you can contract both strains—HSV-1 and HSV-2—in the same or different places.)

What this does mean, though, is that you could give someone else oral herpes or genital herpes, even though you don't have genital herpes. That may sound scary, but it doesn't have to be. Your primary care provider can help you understand the herpes simplex virus and help you take steps to reduce your risk of spreading it to others.

How Do I Know if I Have a Cold Sore?

Cold sores tend to happen in clusters. So if you spot a cluster of small sores on or around your lips, you may be experiencing a cold sore outbreak. 

If you only have one sore, and you can't quite tell what it is, consider paying a visit to your primary care provider or dermatologist. The doctor may be able to tell you have a cold sore just by looking at it. But they'll likely culture the area and run a test to find out, says Michele Farber, MD, a board-certified dermatologist in Philadelphia.

How Can I Get Rid of Cold Sores?

Since herpes simplex virus is a lifelong virus, you can't completely cure it. On the bright side, cold sores will eventually go away on their own within a few weeks. If you're hoping to speed things up or alleviate some of your symptoms, there are some steps you can take.

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Take an antiviral medication

Since cold sores are caused by a virus, you can take antiviral medication to treat them. There are some prescription creams—like docosanol cream or acyclovir cream—you can apply directly to the cold sores. And there are some prescription oral medications—like acyclovir, valacyclovir, or famciclovir—that you can take, as well. “These oral medications are most effective when started quickly and can help shorten the course dramatically,” says Dr. Galaria.

Take a painkiller

If your cold sores are extremely painful, you may want to talk to your doctor about taking some over-the-counter pain medication—like a topical cream or an oral pain medication. Remember, it’s always a good idea to check with your doctor before doing this, especially if you’re regularly taking another kind of medication.

Stay out of the sun

One easy step you can take? Avoid irritating your cold sores. “Keeping the area protected from the sun and avoiding trauma can help with healing,” Dr. Farber says. So wear sunscreen—or stay out of the sun entirely. And be sure not to pop your cold sores as this can allow them to spread further.

Use ice or lip balm to soothe your skin

Ice packs and lip balm won’t make your cold sores go away any faster, but they can soothe your skin, so your cold sores won’t hurt as much. “Ice and lip balms can help with discomfort,” Dr. Galaria says. So give them a try. And stop using them if they don’t seem to be helping.

How to Prevent Cold Sores

There are a few steps you can take to cut down on cold sore outbreaks. For one thing, avoid the irritants that trigger your flare-ups. Protect your skin with sunscreen and use lip balm to keep your lips moisturized.

If these steps don't seem to be helping, talk to your primary care provider. "Some people have so many outbreaks that we actually need to give them prophylactic antiviral medications to keep the virus under control," says Dr. Galaria. This may mean taking a low-dose of an antiviral medication every single day to curb your outbreaks and reduce your likelihood of spreading the virus. 

And even if you don't experience cold sores that often, be sure to tell your doctor that you've experienced them before. "Let your doctors know that you have a history of HSV [before] having any surgical procedures," Dr. Galaria says. Your doctor may instruct you to take an antiviral medication leading up to the surgery to reduce your likelihood of experiencing cold sores as a result of it.