Is a Cold Sore Contagious?

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Physical appearance is one trait many people focus on diligently. That's especially true when it comes to their face. A pleasant smile highlighted by white, shiny teeth tends to elicit one in return. But showing off that smile isn't always easy if you're self-conscious about having a cold sore. For those unfamiliar with cold sores, the sight of one brings about questions, such as how do you get them and is a cold sore contagious?

What Is a Cold Sore?

According to the Mayo Clinic, cold sores are blisters filled with fluid that emerge on or around the lips. Also referred to as fever blisters, they are a fairly common viral infection. The blisters are often clumped together. Once the blister breaks, the remaining sore will be crusted over. The typical healing time frame is two to four weeks with no resulting scar.


A cold sore is caused by the herpes simplex virus (HSV-1). It's similar to HSV-2, which is the virus that results in genital herpes. Unfortunately, there is no cure for either HSV, so it's possible for fever blisters to surface again after subsiding. Signs and symptoms may last several days, while the blisters take two to four weeks to heal completely.

After the initial infection, symptoms may include nausea, vomiting, fever and headaches. Other first-time symptoms may include a sore throat and open sores in the mouth. Symptoms typically emerge approximately one week after the initial exposure to HSV-1.

Cold sores may appear later in life when HSV-1 emerges from being dormant. That can be triggered by poor nutrition, stress, illness or sunlight exposure. Even a dental procedure that stretches the lip can activate the virus. The border of the lip is the most common place for the sores to appear.

The first sign of the sores is a burning, itching or tingling sensation soon followed by swelling and redness. A day or two later, the first blisters appear. The blisters pop resulting in the sores.

Contagious Period

A cold sore is contagious during the short window before it appears and during the time frame it is visible, notes the University of Texas Health Services. However, virus transmission can occur without the presence of oozing blisters. For example, touching the sore and then touching yourself or another person could transfer HSV-1. Other methods of spreading HSV-1 include kissing and sharing eating utensils and towels. Avoiding those various types of interactions may prevent you from contracting the virus in the first place.

Avoid Spreading Cold Sores

For those folks who do occasionally develop cold sores, Nemours offers a few ways to avoid spreading them to others.

  • Clean hands. Diligently wash your hands before touching yourself and others when a cold sore is present
  • Avoid skin-to-skin contact. Since the virus spreads the easiest due to oozing blisters, pay particular attention to coming in contact with others when you're contagious.
  • Do not share items. Avoid sharing items such as cups, utensils and lip balm during the contagious period.

Having cold sores isn't the end of the world, especially once you can answer the question "when is a cold sore contagious?" But whether you do or don't have them, keeping your mouth healthy is of the utmost importance. That starts with brushing at least twice each day followed by consistent flossing. Maintaining a great smile is made that much easier when using Colgate Total Advanced Whitening toothpaste, since it removes 80 percent of surface stains to whiten teeth as it helps prevent plaque, tartar buildup and gingivitis. Remember to schedule regular cleanings with your dentist, too!

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