Call it what you will: cold sore, fever blister, pimple from hell. When you get one, you’re in very good company. “At any given time, between 20% and 40% of the population has cold sores,” says Polina Sayess, MD, a family medicine physician at Dartmouth-Hitchcock Medical Center in New Hampshire. “They’re really common.”

And while these fluid-filled blisters that appear on and around your lips are only very rarely serious, cold sores are no fun. Caused by the herpes simplex virus 1 (HSV-1), they can itch and burn, ooze and crust over. Plus, they hang around for at least a week. But what exactly are cold sores, and why do they just show up from time to time? Here are the facts and myths about these annoying eruptions.

Only adults get cold sores.

False. The HSV-1 virus is so widespread and contagious that many people get their first exposure in childhood. Something as simple as a shared spoon or cup or a kiss from a parent who has a cold sore can do the trick. And that first infection can make kids feel pretty sick. They may have a sore throat and fever along with the blisters.

Once you get a cold sore, you’re immune for life.

False. After your first infection, the virus doesn’t just disappear. It hunkers down and stays inside your body for the rest of your life. “The virus travels to the ganglia, the cluster of nerve cells at the base of your brain, and it sleeps there for years, causing no trouble,” says Dr. Sayess.

“But when your immune system is weakened for any reason, that virus can be reactivated. That’s why it’s important to build up your immunity by eating healthy, getting plenty of sleep and physical activity, and reducing stress.”

Cold sores happen only when you have a cold or during cold weather.

False. The range of possible triggers is wide. “There’s no universal cause,” says Dr. Sayess. “Stress can be a common one. For example, when you feel super angry, the stress associated with that emotion can deplete your immune system.”

Other possible cold sore triggers include hormonal changes (such as those during menstruation or menopause), dental work, and even injuries. A cut to your lip, a laser treatment or cosmetic surgery (or any surgery, for that matter) can cause that sleeping virus to wake up.

As for weather, very cold wind and sun exposure can play a part. How? According to Dr. Sayess, ultraviolet radiation from sunlight might weaken your immune response. And when your lips are exposed to very cold wind, they’re more likely to become dry and chapped, which impairs their protective barrier function. So if you’re sensitive, use a lip balm with sunscreen year-round, whether you’re at the beach or on the slopes.

And yes, a cold or other viral illness can trigger a sore. Here’s why: That new infection in your body can weaken your immune system and give the HSV-1 virus the opening it needs. But remember, you can just as easily get a cold sore when you’re not sick.

Cold sores appear only on your lips.

False.  Though that’s the most common place, it’s not the only one. “You can get cold sores in your cheek or tongue,” says Dr. Sayess. “And if you nibble on your finger during a breakout, you can see blisters forming there, too. You can even transfer the virus to your or a partner’s genital area or to your eyes. That’s rare, but it can be extremely dangerous and cause serious problems with your vision.” If you notice any blisters in your eye area, she advises, get in touch with your health care provider right away.

Cold sores are the same as genital herpes.

Not exactly. Cold sores on the lips are usually caused by HSV-1, while genital herpes is usually caused by a virus called HSV-2. “These 2 viruses are close cousins, and they can both live in either place — on the lips and mouth or in the genital area,” says Dr. Sayess. “Transmission of either virus can be oral to oral (lip to lip) or oral to genital.” That means that it’s possible to get a cold sore from having oral sex with a person who has genital herpes. Your best bet: Be careful about engaging in sexual activities if you or your partner have an active cold sore.

There’s no cure for a cold sore.

True. “It’s a self-limiting condition that usually lasts about 5 to 7 days, and it’s almost never serious,” says Dr. Sayess. “There isn’t a cure for it, though it can make you feel uncomfortable for a while. But there are some very effective treatments that can decrease the severity and duration of the outbreak.” Here are some of the best:

  • Over-the-counter (OTC) remedies. A topical ointment such as Abreva®, which contains the medication docosanol, is the only FDA-approved OTC treatment for cold sores. It can speed the healing process by a couple of days if it’s started at the very first sign of a cold sore. And Blistex®, which contains camphor and phenol, can provide some relief for the pain and itching.
  • Prescription antivirals. Oral medications such as acyclovir (Zovirax®) can be safe and effective. Plus, acyclovir comes in pill or ointment form. Or your provider may prescribe a similar medication, such as famciclovir (Famvir®) or valacyclovir (Valtrex®).

“These are mostly prescribed in pill form and are meant to be taken as soon as you feel an outbreak coming on,” says Dr. Sayess. “You need to take them within 72 hours of noticing your first symptoms, like pain or tingling in your lips. If you have frequent outbreaks, your doctor may prescribe refills so you can have medication on hand as soon as you feel a cold sore coming on.”

  • Home remedies. They won’t heal a cold sore outbreak, but they can help ease symptoms. To lessen pain, you can suck on ice chips. Or you can take a pain reliever, such as acetaminophen or ibuprofen.

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