Cold sores: Everything you need to know

Cold sores are small blisters that appear around your lips or mouth area. Some people call them fever blisters.

They’re caused by a virus that stays in your body for your entire life once you contract it. The virus spreads through contact, like kissing or sharing drinking vessels, with another person who has it.

Because a virus causes cold sores, antiviral medications can help treat them and prevent them from recurring.

Causes of a cold sore

The herpes simplex virus (HSV) is the virus that causes cold sores, specifically herpes simplex type 1 (HSV-1).

Around 67% of the world’s population has the type of HSV that causes cold sores.

You can contract HSV by coming into contact with someone who already has it. You may still contract the virus even if the person doesn’t appear to have any symptoms at the time.

This can occur via:

• touching cold sores
• touching saliva
• sharing cups or silverware
• sharing cosmetics like lipsticks

When the virus is inactive, cold sores don’t develop. When it becomes active again, cold sores may form.

Certain triggers can reactivate the virus. For example, sunlight, stress, and menstruation can reactivate HSV-1 infections and trigger the formation of new cold sores. Other triggers include:

• illness
• fever
• injury or cuts
• surgery

Risk factors

According to a 2019 study, the following may increase your risk of contracting a herpes simplex infection:

• having an income that falls below the poverty level
• living in an urban area
• having multiple siblings

The same study also notes that in women over age 64 years, kidney disease was a risk factor for HSV activation.

Is a cold sore the same as herpes?

A specific type of herpes, HSV-1, causes cold sores.

Along with herpes simplex type 2 (HSV-2), HSV-1 can cause genital herpes. You can spread or contract herpes through oral sex.

However, HSV differs from the varicella-zoster virus, which causes chickenpox and shingles (also called herpes zoster).

How long are cold sores contagious?

Cold sores are generally at their most contagious when you have an outbreak, though you may still spread the virus even when you don’t have any symptoms.

They are typically most contagious from when you first notice one forming, which often begins with a tingling sensation before you notice an actual sore forming. This will likely last up to 2 weeks.

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Cold sore symptoms

Cold sores are fluid-filled blisters. They may crust over with time. They can appear around or inside your mouth and on and around your lips.

People with cold sores can also develop ulcers in and around the mouth area. These sores and ulcers can be painful and may crack and ooze.

The first time you contract HSV-1, you may also develop:

• fever
• body aches
• sore throat
• headache
• swollen lymph nodes

If you have a cold sore, it means the virus is active and you can pass on HSV-1 to others.

Treatments

HSV-1 has no cure. Once you have the virus, it stays in your body for life.

Treatment for cold sores is not always necessary, though. Many cold sores disappear on their own within 1–2 weeks.

You may need treatment if you:

• have eczema
• develop a cold sore near an eye
• develop several cold sores
• have cold sores that are very painful
• have a cold sore that lasts longer than 2 weeks
• take medication or have a condition that weakens your immune system
• recently had treatment that weakens your immune system

People who develop cold sores six or more times per year should also receive treatment. This may involve taking a low dose of antivirals every day.

Antiviral medications can help heal cold sores and reduce pain. They can also prevent more serious HSV-1 infections. There’s no scientific evidence that some antiviral treatments are better than others. A 2021 research review notes that combining specific treatments can be more effective than using them alone.

These medications include:

• acyclovir cream (Zovirax and Xerese)
• acyclovir (Sitavig, Zovirax)
• valacyclovir (Valtrex)
• famciclovir (Famvir)

Wearing lip balm with a sun protection factor (SPF) of 30 or higher can also help heal or prevent sores if sunlight is a cold sore trigger for you.

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Summary

Cold sores result from an HSV-1 infection. They are painful, fluid-filled blisters that form in and around the mouth and may crack and ooze.

There’s no cure for HSV-1. But antiviral creams and oral medications can help reduce the symptoms of cold sores and prevent you from spreading the virus to others.

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