Herpes labialis, also known as cold sores or fever blisters, is a very common viral infection. While highly unpleasant and uncomfortable, it is not a serious condition in itself. It can, however, pose a problem for people whose immune systems are weakened by disease or medication (ex: cancer, HIV, AIDS, immunosuppressive drugs).


The virus responsible for cold sores is the Herpes simplex virus (or HSV). There are two main strains of this virus: HSV-1 and HSV-2. The same virus is also responsible for genital infections. HSV-1, which causes cold sores on the lips, is usually acquired in childhood, while exposure to HSV-2, which results in genital diseases, occurs with the onset of sexual activity. Furthermore, both types of viruses can be passed from the lips to the genitals, or vice versa, through direct contact (kissing, oral sex). Most adults are already infected with one of the viruses responsible for this infection (50% with HSV-1 and 17% with HSV-2).


The first episode usually occurs in childhood and is often symptom-free. However, if symptoms are present, they are likely to be pronounced. Difficulty swallowing may occur if the lips and inside of the mouth are affected. Fever is another common symptom. It may take up to 14 days for the sores to heal. Once contracted, the virus remains in the body for life. Some people never have a second episode, while others experience several recurrences.

Recurrences are preceded by warning symptoms called prodromes. These include a tingling, itching, burning or numbing sensation around the lips or swelling. This is followed by the appearance of painful pinkish lesions that look like fluid-filled blisters. These may burst and form crusts as they dry. The lesions can spread to the inside of the mouth (inside of the cheeks, tongue, throat) and the nose. The virus can also spread to other areas such as the eyes, breasts and genitalia through infected secretions. A person can transmit the virus even when there are no visible lesions.


Herpes labialis is diagnosed by a physician who will conduct a visual examination of the lesions and will ask the patient to answer a few questions. Additional tests, including blood tests, are generally not required to diagnose this infection.


Over the counter and prescription antiviral medication is available. Some medications are taken orally, while others are applied locally. They can help reduce healing time and the spread of sores if started at the first sign of symptoms (prodrome). However, no one medication can eliminate the virus from the body. Analgesics such as acetaminophen (Tylenol®) or ibuprofen (Advil®) can be taken to relieve pain associated with herpes labialis. Additional relief can be obtained by applying ice on the lesions.


To prevent children and adults from spreading the virus, it is important to avoid sharing items that come into contact with the mouth and to avoid kissing anyone with active oral lesions. Also, physical protection (ex: latex or polyurethane condoms, dental dams) during oral-genital contact as well as hand washing after touching lesions is recommended to prevent virus transmission.

Those who have already contracted the virus should:

  • ensure that their lips are well hydrated (moisturizing lip balm);
  • apply sun protection on and around their lips before going out in the sun;
  • maintain a healthy lifestyle (sleep, nutrition, exercise);
  • have an up to date prescription for an antiviral that can be started at the first signs of prodrome.
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