The Facts About Cold Sores

By Stuart Maddin, MD, FRCPC

Cold sores, or fever blisters, are common among Canadians.

Read the facts about cold sores and the virus that causes them.

Fact: Cold sores are caused by a virus

  • Cold sores are caused by the herpes simplex virus. There are two types of this virus and cold sores are usually caused by type 1 (known as HSV-1). The other type of herpes simplex virus, HSV-2, usually causes genital herpes
  • In general, we are infected with HSV-1 when we are children; in the majority of these initial (“primary”) infections, there are no symptoms
  • Usually, the virus infects our mouths. Some children experience mouth and gum symptoms (“gingivostomatitis”) or a sore throat (“pharyngitis”).

Fact: Cold sores are the result of the virus reactivating in our bodies

  • Once HSV-1 has entered our bodies, it never leaves. The virus moves from the mouth to quietly reside (“remain latent”) in the central nervous system.
  • In approximately one third of people, the virus can “wake up” or reactivate to cause disease
  • When reactivation occurs, the virus travels down the nerves to the skin where it may cause blisters (cold sores) around the lips, in the mouth or, in about 10% of cases, on the nose, chin, or cheeks
  • Many people who suffer from cold sores are aware in advance that a cold sore is about to break out — they have a tingling or burning feeling, redness, itching, or pain (“prodromal symptoms”) around their lips or mouth
  • Cold sore outbreaks may be influenced by stress, menstruation, sunlight, sunburn, fever, or local skin trauma.

Fact: The virus that causes cold sores is infectious

  • 30%-60% of children below 10 years of age are infected with HSV-1. They have acquired the virus from family and friends through sharing utensils or toothbrushes, and from kissing
  • The virus is transmitted from cold sores and also when there are no symptoms, as it can make copies of itself on the skin in the absence of a blister. This phenomenon is called “asymptomatic shedding”
  • By 50 years of age, 80%-90% of us harbour HSV-1 because we have caught it from someone close to us
  • HSV-1 can sometimes be transmitted to newborn babies by family members or hospital staff who have cold sores; this can cause a severe disease called neonatal herpes.

Fact: The virus from cold sores can infect other areas of the body

  • People can transfer the virus from their cold sores to other areas of the body, such as the eye, skin, or fingers; this is called “autoinoculation”
  • Eye infection, in the form of conjunctivitis or keratitis, can happen when you rub the cold sore, then rub your eyes before washing your hands
  • Finger infection (“herpetic whitlow”) can occur when a child with cold sores or primary HSV-1 infection sucks his/her fingers
  • HSV-1 can infect your genital area if you engage in oral sex with a partner with a cold sore

Fact: Early treatment can help eliminate the cold sore

  • Some products can accelerate healing if they are used at the prodromal stage of the cold sore
  • Prescription drugs include acyclovir cream or capsules (Zovirax®) and penciclovir cream (Denavir®); also, Health Canada recently approved a one day course of 2 grams valacyclovir caplets (Valtrex®) for prodromal use
  • Docosanol cream (Abreva®) can be bought without a prescription
  • Frequent hand washing minimizes the risk of transferring the virus to other areas of your body

About the author:
Dr. Stuart Maddin is past President of the Canadian Dermatology Association and served as Secretary-General of the International Committee of Dermatology — International League of Dermatological Societies. He is the director of the clinical trials unit at the Division of Dermatology, UBC. Dr. Maddin has also acted in an advisory capacity to the Health Protection Branch (Ottawa), the AAD-FDA Liaison Committee and WHO (Geneva).


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