What is a cold sore?

A cold sore, also known as oral herpes or a fever blister, is a small blister on or near your lips and mouth caused by a viral infection.

After contact with an infected person, the virus replicates on your skin and produces open, painful blisters that last a week or longer. Once infected, cold sores will remain dormant inside nerve cells and activate periodically throughout your life.

Causes of a cold sore

Cold sores occur in reaction to the herpes simplex virus (HSV-1), which is widespread and often acquired during childhood. Most commonly, cold sores are the result of an HSV strain which is passed through saliva or direct oral contact from someone who is infected – this includes sharing drinks and utensils.

After the initial break out, triggers such as fever, stress, sunlight or a cold can cause a subsequent breakout. Although most people who have cold sores break out two or fewer times a year, some people have monthly breakouts.

Occasionally, herpes simplex virus - 2 (HSV-2), which causes genital herpes, can spread through oral sex, resulting in cold sores on your mouth.
HSV infections are lifelong and contagious even when symptoms aren’t present.

Risk factors for a cold sore

Anyone who has come into contact with HSV-1 is susceptible to cold sores, but having an infection does not guarantee a cold sore outbreak. Many people live with the virus the rest of their lives and do not develop cold sores.

Symptoms of a cold sore

More than 65% of patients who have HSV-1 virus in their bodies will never show symptoms but can transmit the disease to others who may.

For those who suffer from cold sore breakouts, symptoms include:

  • Tingling or itching inside the mouth
  • Painful, red spot typically appearing on the lips
  • Blister outbreak along the mouth, possibly filled with fluid
  • Mouth sores that may open, ooze and scab over

Diagnosis of a cold sore

Cold sores can be diagnosed by a primary care provider — although this is typically not necessary to identify and treat them. If an outbreak is severe and limits your ability to speak or swallow, you may schedule an appointment with your Mercy Health primary care provider.  

Your doctor may order a culture of the fluid from a cold sore to determine if the HSV virus is causing he break out.

In severe cases, you may be referred to a dermatologist to treat your condition.

Treatments for a cold sore

In severe cases of a cold sore outbreak, topical or oral antiviral medications might be prescribed to fight the infection. If these medications do not work, IV antiviral medication may be necessary.

If you suffer from frequent cold sores, a prescription topical cream can be prescribed to reduce the length and severity of your breakout. 

Cold sore symptoms can be treated with:

  • Cold sore medication — over-the-counter ointments like docosanol and benzocaine can help ease pain and promote healing.
  • Cool compress — can relieve the pain caused by the blisters.
  • Lip balm or petrolatum — can help keep the sore from splitting or cracking.
  • Pain medication — if your cold sores are causing pain, over-the-counter pain relievers can be used to eliminate the pain.
  • Sunscreen — as sores are healing, wear sunscreen (SPF 30 or higher) to protect your lips from the sun.

Any creams or balms should be applied with a clean Q-tip each time to prevent spreading the cold sores.

Recovery from a cold sore

Cold sores will heal on their own within 1-2 weeks, but some topical medication can shorten the duration.

Since HSV is a lifelong infection, it is common for cold sores to recur (often during times of stress or sickness). Not everyone infected with the virus will develop cold sores or having recurring outbreaks.

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