Cold Sores

By David A. Thompson, M.D. 
March 22, 2017

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Cold Sores

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Cold Sore of Lower Lip


  • A cluster of painful tiny (1-3 mm) small bumps or blisters on the outer lip. Typically, there are 3-5 blisters within a ½ inch (12 mm) area. The small blisters often rupture and form 1 big sore (i.e., cold sore)

  • Present only on one side of the mouth (i.e. doesn't cross the midline).

  • Also referred to as Fever Blisters

General Information

  • Cause: Cold sores are recurrent painful blisters on the outer lip caused by the Herpes simplex virus (usually Type I).

  • Primary Herpes Simplex: Approximately 80% of the adult population has had herpes simplex at some point in their lives. The very first episode (primary herpes simplex) of infection can present as sores on the inside of the mouth (with fever and feeling sick). More commonly, people have no symptoms at all during the first episode.

  • Recurrent Herpes Simplex Labialis (Cold Sores): After the first episode of Herpes, the Herpes virus stays hidden in a facial sensory nerve. It can be reactivated by sun exposure, fever, friction, trauma, menstrual periods, stress or physical exhaustion. Such recurrences occur in 20% of the adult population. Typically, the symptoms are confined to the lip and there is no fever. The medical term for these recurring cold sores of the lip is Herpes Simplex Labialis. Another term that people use for this condition is Fever Blisters. This is a self-limiting illness that resolves without any treatment in 7 -10 days.

Are there any over-the-counter treatments for cold sores?

  • Docosanol cream (Abreva) seems to reduce severity, pain and duration of cold sores (Sacks 2001). Docosanol is FDA approved in the United States. Ask your physician's opinion.

What can your physician prescribe for colds sores?

  • Topical (cream) prescription treatment with Pencylcovir 1%: Use of this cream four times daily has been shown to reduce the severity, pain and duration of cold sores in adults (Spruance 1997). It is more expensive than docosanol.

  • Oral (pills) prescription treatment - Available oral anti-viral medications include acyclovir (Zovirax), famcyclovir (Famvir), and valacyclovir (Valtrex). There may be some modest benefit obtained from using these medications; these medications may shorten symptom duration by 1 day and reduce symptoms. However, the research is not conclusive and such treatment is not standard practice (Emmert 2000). You will need to discuss this with your physician.

If not, see these topics


When to Call Your Doctor

call now

Call Your Doctor Now (night or day) If

  • You feel weak or very sick

  • Sores on the eye, eyelids or tip of nose

  • Red streak or red area spreading from the cold sore

call within 24 hours

Call Your Doctor Within 24 Hours (between 9 am and 4 pm) If

  • You think you need to be seen

  • Have a weakened immune system (e.g., HIV positive, cancer chemotherapy, organ transplant, splenectomy, chronic steroid therapy)

  • New sores occur in another area

call within 24 hours

Call Your Doctor During Weekday Office Hours If

  • You have other questions or concerns

  • You are worried you might have a sexually transmitted disease

  • Cold sores are a recurrent problem, and you want a prescription medicine to take the next time they occur

  • Cold sore last longer than 10 days

home care

Self Care at Home If

  • Cold sore and you don't think you need to be seen



  1. General Information - Cold Sores

    • Fever blisters or cold sores occur on one side of the outer lip.

    • Typically lasts 7-10 days.

    • Treatment with a cold sore cream can reduce the pain and shorten the course by a day or two.

  2. Docosonal 10% Cream:

    • Apply over-the-counter docosanol cream (trade name Abreva) to the cold sore 5 times daily until healing occurs.

    • Begin using this cream as soon as you first sense the beginning of an outbreak.

    • Docosonal is not available in Canada.

    • Read and follow the package instructions. Ask your physician's opinion.

  3. Contagiousness:

    • Herpes from cold sores is contagious to other people. Try not to pick or rub the sore. Do not open the blisters. Wash your hands frequently. The cold sores are contagious until dry (approximately 5 days).

    • Most cold sore sufferers note a tingling in the lip before the sore appears (prodromal phase). Patients are also contagious during this time period.

    • Eyes - Avoid spreading the virus to someone's eye by kissing or touching; an eye infection can be serious (Herpes keratitis).

    • Mouth - Since the blisters and mouth secretions are contagious, avoid kissing other people during this time. Avoid sharing drinking glasses, eating utensils, or razors.

    • Sex - Avoid oral sex during this time. Herpes from sores on your mouth can spread to your partner's genital area.

    • Contact with Immunocompromised People - Avoid contact with anyone who has eczema or a weakened immune system.

  4. Expected Course: The pain typically subsides over 4-5 days and the sores typically heal over a 7-10 day period. On average, patients note recurrences 2-3 times per year.

  5. Prevention: Since cold sores are often triggered by exposure to intense sunlight, use a lip balm containing a sunscreen (SPF 30 or higher).

  6. Recurrence: Tingling or burning on the outer lip where cold sores previously occurred is an early sign of the new onset of recurrent cold sores.

  7. National Herpes Hotline: Phone number - (919) 361-8488. Counselors provide information about transmission, treatment, prevention, and emotional issues. The hotline is open from 9 AM to 7 PM, Eastern Time, Monday through Friday.

  8. Call Your Doctor If:

    • Sores look infected (spreading redness)

    • Sores occur near or in the eye

    • Sores last longer than 10 days

    • You become worse

And remember, contact your doctor if you develop any of the "Call Your Doctor" symptoms.


March 22, 2017