Cold Sores (Fever Blisters) Caused By Herpes Simplex Virus

What are cold sores?

Cold sores are painful, highly contagious, fluid filled blisters most commonly occurring on the lips or around it. Also known as fever blisters, it tends to appear in groups and with time the blisters burst and crust over leading to the formation of the typical sores. Cold sores are caused by the herpes simplex virus (HSV 1) infection. Usually the ulcers heal within two weeks without any intervention but tend to recur. There is no permanent cure for cold sores (herpes infection) although antiviral drugs hasten recovery and reduces the frequency of attacks of cold sores. The infection is slight more common in women than men.

Signs and Symptoms

Often HSV 1 infection does not produce any symptoms. Cold sores are just one presentation of HSV-1 infection. These sores appear as fluid filled blisters on the :

  • Lips
  • Gum
  • Oral cavity
  • Upper throat

There may be warning symptoms that are experienced before the development of the cold sores. This includes tingling, burning and an itching sensation at the affected site. Sometimes the blisters are associated with :

  • Fever
  • Swollen, painful neck glands (lymph nodes)
  • Pain during swallowing
  • Headache
  • Malaise – a feeling of weakness
  • Generalized body pain

Blisters usually occur in groups and small blisters may merge together in a one large blister. Once it bursts, it may form an ulcer and crust over. The ature and severity of symptoms vary depending on whether it is the first attack or recurrence. In children the cold sores from mouth may spread to other parts of the body, namely the fingers and around the eyes as painful blisters.

Causes of Cold Sores

Cold sores are due to a viral infection and is not a result of a fever, despite the common term fever blisters. It is caused by the herpes simplex virus type 1 (HSV-1). The other type of herpes (HSV-2) causes genital herpes although HSV-1 can cause genital ulcers and HSV-2 can lead to oral lesions. The infection spreads from active lesion of one person to another person through close contact. HSV 1 spreads by sharing the same razor, utensils, towels or kissing.

Although the most common source of oral herpes infection is the oozing fluid from the blister, the virus can even spread from persons without any blisters. A person once infected with herpes virus harbors the virus throughout his life. The virus remains in dormant (latent) phase in the nerve cells of the body and causes active infection (painful blisters in the facial region) in between periods of remission.


Recurrent attacks of herpes virus is precipitated by :

  • Stress
  • Menstruation
  • Fever
  • Sunlight

Risk factors

Most adults, including those who have never exhibited any symptoms of herpes infection, show positive result for herpes infection (HSV-1). Risk factors for development of HSV-1 are :

  • Close contact with persons with active infection (usually with oozing blisters).
  • Weak immune system: HIV patients, treatment with cancer drugs, long term steroid treatment.
  • Burns.
  • Eczema.
  • Emotional stress.

Cold Sore Treatment

Cold sores usually heal without any treatment within one to two weeks. Antiviral drugs like acyclovir, valacyclovir, famicyclovir are prescribed to hasten recovery and prevent recurrent attacks. Painkillers are sometimes prescribed to relieve pain. It is important for patients to realize that it can recur as HSV-1 infection lasts for a lifetime. Therefore it is important to identify possibly triggers and avoid it as part of the long term management of cold sores.

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