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What are cold sores?

Cold sores are small blisters around the mouth, caused by the herpes simplex virus. They are sometimes called fever blisters. The most common strain of the virus causing cold sores is herpes simplex virus 1. It can be spread by kissing or sharing eating utensils or even sharing towels. 

Herpes simplex is not curable but may lie dormant for a long time.


What causes cold sores?

Cold sores are caused by the herpes simplex virus. Once the herpes simplex virus is in you, it can cause outbreaks of cold sores. Cold sore outbreaks are often triggered by exposure to hot sun, cold wind, a cold or other illness, a weak immune system, or even stress.


What are the symptoms of cold sores?

Some people don’t have any symptoms with the first attack. Others have flu-like symptoms and ulcers in and around the mouth. While each person may experience symptoms differently, these are the most common:

  • Tingling of the lips, commonly felt before cold sores appear 
  • Small blisters on the lips and mouth that enlarge, burst, then crust over
  • Itching, dryness, and irritation of the lips and mouth
  • Soreness of the lips and mouth


How are cold sores diagnosed?

Your physician can often diagnose cold sores by examining the sores. If the diagnosis is unclear, he or she may culture or obtain a sample of the sore for a DNA PCR test specific for the virus using a swab.


How are cold sores treated?

Cold sores can’t be cured, but, if symptoms are severe, treatment may help relieve some symptoms. Treatment may include:

  • Antiviral topical ointments (such as acyclovir and penciclovir) have been shown not to be very beneficial (see Can cold sores be prevented?)
  • Antiviral oral medicines (such as acyclovir, famciclovir, and valacyclovir) may decrease the time the sores are present or their severity
  • Over-the-counter topical anesthetics or anti-inflammatory agents may help with symptoms

Cold sores take about 1 to 3 weeks to heal. The first time they appear, they can take up to 3 weeks to heal. But, when cold sores return, they usually are less severe and take a week to heal if no medicines are used. Antiviral medicines may help but work best if begun with initial symptoms before a blister even appears. Antivirals are usually not recommended for otherwise healthy people. Always talk your physician or dentist if the sore does not heal or becomes worse as time passes. 


Can cold sores be prevented?

If you have never had a cold sore, avoid skin-to-skin contact with someone who has an active cold sore. If you have had a cold sore, you may prevent or reduce the number of recurrences by determining what triggers your outbreaks and avoiding the trigger. For instance, if sun exposure is a trigger, use sunscreen when in the sun. If you have outbreaks often, talk with your healthcare provider. Starting treatment as soon as you know you are developing a cold sore can promote healing and reduce the time it takes a cold sore to heal.

The long-term use of oral antiviral agents can prevent cold sores, but the benefit is very small. This approach is usually used only for people who get frequent and painful cold sores. Some evidence shows that topical antiviral medicines have no desired effect or that their effect in preventing cold sores could not be confirmed.