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

Kathy Heydasch

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.

A fever blister can cause a moderately high fever.
A fever blister can cause a moderately high fever.

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.

Herpes simplex 1 lesions that occur on the lips are often known as cold sores or fever blisters.
Herpes simplex 1 lesions that occur on the lips are often known as cold sores or fever blisters.

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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Discussion Comments


Herpes simplex type two causes fever blisters on the lips as well. And a herpes simplex type two outbreak is often accompanied by a fever. But this type of herpes also causes genital blisters.

The best way to avoid cold sores or fever blisters it to take supplements like lysine when one feels the blister coming on. Before a blister pops up, there is usually itching and discomfort on my lip. As soon as I start feeling this, I take lysine capsules that I get from the pharmacy. The blister usually doesn't develop if I start taking lysine early.


@SteamLouis-- I'm not a doctor but I think it can happen both ways.

Herpes simplex type one causes cold sores/fever blisters on the lips. This is actually very common and a great percentage of the population carries the virus. When an individual gets the virus, the virus lies dormant in the body. When the immune system has weakened, the virus becomes active and causes cold sores or fever blisters. Since the virus has become activated, a mild fever can develop. It's also possible for a fever blister to show up when the body is dealing with a different infection. So you are right that the fever does not have to be because of the blister.

And cold sores have many triggers. I usually get them in winter when my lips crack due to the cold and I suppose my immune system weakens in winter as well.


I always thought that a fever causes fever blisters. How can fever blisters be the cause of fever?

And cold sores sometimes occur even without a fever right?

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