Sunlight can trigger cold sores on the lips — here's how to stop them

If you feel a cold sore coming on, follow these tips to treat it ASAP before it blisters and scabs.
Close-Up Of Young Woman Against Wall At Home
“The sun suppresses the immune system in the skin a little bit, and that lets the virus in the nerves reactivate and cause a cold sore,” said Dr. Melissa Piliang.Maria Maglionico / EyeEm / Getty Images stock

Cold sores are blisters, or clusters of blisters, that crop up on your lips or near your mouth. They are also sometimes called fever blisters.

A virus called the herpes simplex virus causes cold sores. It’s a common, highly contagious virus. According to the American Academy of Dermatology (AAD), more than half of people age 14 to 49 in the U.S. have the virus. Canker sores are sometimes confused with cold sores. But they aren't the same. Canker sores typically appear inside the mouth and are not contagious.

Symptoms of cold sores

Cold sore symptoms can vary depending on whether you contracted the virus for the first time or it’s flaring up again.

New infections almost always occur in children, since the virus is so contagious. The AAD says children usually feel sick — they may have a sore throat, fever, body aches, headache or nausea. They may have cold sores on the lips, tongue, gums or throat.

Once you’ve had cold sores, you’ll likely notice some warning signs before they reappear, such as burning, stinging, throbbing, itching or tingling.

“Most people, after they’ve had cold sores a couple of times, know when they’re going to come on even before blisters appear. I encourage them to keep treatment on hand. When they feel that tingly sensation, they can start treatment right away. You don’t want to wait until you have big blisters that are scabbed over. The sooner you start, the better the results,” said Dr. Melissa Piliang, a dermatologist at the Cleveland Clinic and a member of the American Academy of Dermatology.

You’ll usually form a cold sore inside the lips or near your mouth. Sometimes, they show up on other parts of your face. You can spread them if you touch the cold sore, then touch someplace else on your body.

Cold sores break open and scab within 48 hours and resolve within five to 15 days, according to the AAD.

Causes of cold sores

Once you contract the herpes simplex virus that causes cold sores, it travels to your nerves and never goes away. Your cold sores can subside, but the virus can reactivate later and cause new ones.

The AAD says these factors can trigger new outbreaks:

  • Stress
  • Fatigue
  • Fevers, colds or flus
  • A cut or injury where you’ve had cold sores before
  • Dental work, cosmetic surgery or laser treatments
  • Hormonal changes
  • Sunlight

“The sun suppresses the immune system in the skin a little bit, and that lets the virus in the nerves reactivate and cause a cold sore,” said Piliang.

If you know you’re going to be exposed to a trigger, be ready with your medicine for cold sores and begin treating it as soon as you feel one coming on.

Because the virus that causes cold sores is so contagious, you should be careful not to spread it to other people.

The AAD says you should avoid:

  • Kissing or other intimate contact
  • Babies, people with weakened immune systems and children with eczema
  • Sharing food, drinks, towels, razors or lip balm
  • Touching your cold sore — if you do, wash your hands right afterward

Diagnosing cold sores

Your dermatologist can probably diagnose cold sores by their appearance. A swab from the sore can be tested to see if it shows the herpes simplex virus. And a blood test can determine if you’ve been exposed to the virus, said Dr. Jenny Murase, associate clinical professor of dermatology at the University of California, San Francisco, and a member of the American Academy of Dermatology.

Herpes simplex virus causes cold sores — it’s a common, highly contagious virus. ancoay / Getty Images stock

Treatment for cold sores

Most cold sores are not serious and will clear up in two weeks or so even without treatment, according to the AAD. Over-the-counter medications can help with getting rid of cold sores more quickly. The AAD says to look for the ingredients docosanol or benzyl alcohol.

See your dermatologist if:

  • Your cold sore lasts longer than 15 days. Your dermatologist knows how to get rid of a cold sore and may prescribe creams that you can apply to the sores, or an antiviral medication that you take by mouth. If your cold sores still don’t clear up, your doctor might suggest IV antiviral medication.
  • You get cold sores frequently — several times a month. “You can take a prophylactic antiviral medication every day,” Murase said.
  • You have a cold sore close to your eye, since the virus could spread and affect your vision.

It’s important to protect your lips and skin with sunscreen when your cold sores are healing, and sun protection all the time can help keep new cold sores from cropping up.