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Cold sores are caused by the herpes simplex virus type 1. This virus is very contagious, meaning that cold sores are contagious until they go away completely, which usually takes about two weeks.

Cold sores are small, fluid-filled blisters that usually appear on or around the lips and mouth. They can appear on their own or in small clusters.

In most cases, the blisters will break, creating a scab that eventually falls off. Cold sores are caused by the herpes simplex virus type 1 (HSV-1).

HSV-1 is very contagious. You can spread the virus even when you don’t have any symptoms of a cold sore, though you’re usually most contagious when you have them. However, this is much less likely than if contact occurred when a cold sore was present.

Cold sores are contagious until they go away completely, which usually takes about two weeks. This means the common belief that cold sores aren’t contagious once they’ve scabbed over isn’t true.

Keep reading to learn more about how cold sores spread and how you can protect those around you when you have one.

HSV-1 is spread by close contact with skin or saliva, such as kissing, oral sex, or even sharing eating utensils or towels. The virus enters the body through a break in the skin, such as a small cut.

Once you’ve contracted HSV-1, you have it for life.

However, some people with HSV-1 never have any symptoms. This is because the virus can lie dormant in your nerve cells until something triggers its reactivation. You can still pass the virus to other people while it’s dormant.

Things that can reactivate HSV-1 include:

HSV-1 is very common. According to Johns Hopkins Medicine, about 50 percent to 80 percent of people in the United States are living with HSV-1. In addition, most adults are exposed to the virus by the age of 50.

However, reactivation of the virus tends to decrease in people over the age of 35.

If you’re worried someone may have spread the virus to you, keep an eye out for these early signs in any spots near or around your mouth:

  • tingling
  • swelling
  • soreness

If you’ve never had a cold sore before, you might also notice:

  • fever
  • painful mouth sores on your tongue or gums
  • sore throat or pain while swallowing
  • swollen lymph nodes in your neck
  • headache
  • general aches and pains

There’s no way to get rid of HSV-1 once you have it. However, there are several things you can do to help manage your symptoms.

Prescription antiviral medication can help speed up the healing process of cold sores. These often come as either pills or creams.

For severe infections, you may need an injection of antiviral medication. Common antiviral medications for cold sores include valacyclovir (Valtrex) and acyclovir (Zovirax).

You can also use over-the-counter cold sore treatments, such as docosanol (Abreva), to help heal cold sores.

Shop online for cold sore treatments.

To reduce redness and swelling, try applying a cold compress or ice cube to the area. You can also take nonsteroidal anti-inflammatory drugs, such as ibuprofen (Advil), to reduce inflammation.

If you have cold sores, you can help prevent transmission of HSV-1 by:

  • avoiding close physical contact, such as kissing or oral sex, until the sore is fully healed
  • not touching your cold sore unless you’re applying a topical medication
  • not sharing items that might have been in contact with your mouth, such as eating utensils or cosmetics
  • being extra careful about avoiding close physical contact with babies and people with weakened immune systems, who are both more vulnerable to infection

Cold sores are small blisters that occur on and around your lips and mouth. They’re caused by a virus called HSV-1. Once you contract HSV-1, you have the virus for life. While you’ll always be able to spread the virus, you’re most contagious when you have an active cold sore.