What Is the Difference Between a Cold Sore and a Fever Blister?

A cold sore, also known as a fever blister.
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  • Written By: Kathy Heydasch
  • Edited By: O. Wallace
  • Last Modified Date: 16 April 2014
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There is no difference between a cold sore and a fever blister. Both refer to the same type of lesion that appears on the face, mostly around the mouth, as a result of the herpes simplex virus, either type 1 or type 2. The sores can be uncomfortable, sometimes painful, and can last up to 2 weeks.

The typical length of an outbreak is 8-12 days, after which the virus subsides and the cold sores and fever blisters heal. As the name implies, a fever blister or herpes simplex outbreak can cause a mild fever. Treatment for the headaches can be simple over-the-counter medicine. Treatment for a cold sore and a fever blister may include topical ointments or skin creams which might lessen the intensity of the outbreak. It is possible to have the herpes simplex virus and never have an outbreak.

At the beginning of an outbreak, the area will become reddened and sore. Then a blister forms, and the blister becomes an ulcer. Sometimes a cluster of small blisters can join to form one large lesion. After the ulcer stage, the area scabs over and eventually heals.


There is no cure for the herpes simplex virus, only some medicines that can help reduce the severity of the outbreak. The disease is highly contagious as well. If a cold sore and a fever blister form, one should take great care to avoid spreading the virus. This includes not sharing cups, silverware or even food with another. The herpes type 1 virus can also be transmitted through kissing an infected person when an outbreak is evident.

A cold sore and a fever blister are most contagious during what is known as the weeping stage after the blisters break and the ulcer is active. The liquid that seeps from a cold sore and a fever blister is packed with millions of herpes simplex cells. Although it is most contagious at this stage, a cold sores and a fever blister is contagious even from the initial reddening. Additionally, a person can transmit the virus to other parts of the body, including the hands and eyes.

There is a difference between cold sores and canker sores. Canker sores form on the inside of the mouth and are not considered to be contagious. They involve the same type of blister and ulcer, but do not form scabs because of the moisture inside the mouth.


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