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Cold Sores - How to Prevent and Treat Them

By Bonnie Kuehl, PhD

Cold sores are very common and quite contagious. Sometimes referred to as fever blisters, cold sores are caused by the herpes simplex1 virus (HSV-1). Learn more about HSV-1 on Herpes Guide.ca. They can appear as a single blister or cluster of them, often recurring in the same location, including on and around your lips, nose, chin or cheeks. Cold sores are often confused with canker sores, but canker sores are actually sores or ulcers that occur inside your mouth, and are not contagious.

Causes and Triggers

An estimated 1 in 5 Canadians is affected by cold sores each year, and on average people experience 2 to 3 outbreaks per year. We are usually infected by the virus when we are children, and once the virus enters our bodies it never leaves. Most of the time the virus quietly hides or sleeps in our central nervous system, but certain triggers cause it to "wake up" and cause cold sores. Common triggers include stress, menstruation, sunlight, fever, dry chapped lips, or local skin trauma.

How A Cold Sore Develops

Many people who suffer from cold sores know when one is coming by the distinctive (and often dreaded) tingling or burning, redness, itching or pain they feel around their lips or mouth. This is the first stage of a cold sore and these symptoms are sometimes called prodromal symptoms. This first stage can happen very quickly - from a few hours to a day or two. You might even go to bed without any symptoms and wake up to find you have a cold sore!

The next stage of a cold sore is the formation of one or more blisters. After the blister(s) has developed, it breaks and an unsightly yellow crust forms. Within a few days this crust falls off and leaves behind a pinkish skin that heals without a scar. The entire process usually takes between 8 to 10 days.

It is important to remember that cold sores are contagious. The virus can be passed from person to person and from one area of your body to another through skin-to-skin contact - even when blisters are not present. The virus is often transferred by kissing or oral sex, as well as by hands or fingers that have touched a cold sore. The virus can even be passed by sharing cups, cans, glasses, eating utensils, towels and food items such as sandwiches.


You can't cure or prevent cold sores, but you can take steps to reduce how often they occur and shorten the length of an outbreak.

Cold sores often clear up without treatment in 7 to 10 days. Early treatment during the initial tingling or burning stage may stop the blister from forming, or help the cold sore heal faster once it has formed. It's good to know that there are certain non-prescription and prescription products that can help, including Abreva, Lipactin, Zovirax, Denavir and Valtrex. Your pharmacist or family doctor can advise you on which treatment is best for you. You can learn more about these treatments at Herpes Guide.ca.


You can take steps to guard against cold sores - to prevent them from occurring and to prevent the virus from being passed to other parts of your body or to other persons:

  • Use a lip moisturizer regularly to prevent your lips from becoming dry or chapped.
  • Try to avoid cold sore triggers such as stress or overexposure to the sun.
  • Limit your exposure to the sun or UV lamps, and always use a sunscreen lip balm with an SPF of at least 15.
  • During times of high stress, consider trying relaxation therapy.
  • Keep your immune system strong by maintaining a healthy diet and getting enough sleep.
  • Avoid kissing and skin contact with people, especially children, while blisters are present.
  • Avoid sharing food, cups/glasses/cans, utensils and towels when blisters are present.
  • Keep your hands clean - wash them frequently to avoid passing on the virus or infecting other areas of your body.

About the author:
Bonnie Kuehl, PhD, Experimental Therapeutics/Cancer Biology, University of Toronto/Ontario Cancer Institute, and an Honours BSc in Biochemistry, University of Guelph. Post-doctoral Fellowships in the laboratories of Sir Professor David Lane, Scotland, U.K. and Dr. Silvia Bacchetti, McMaster University. Key areas of interest include biochemistry as well as cell and molecular biology.

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