Cold sores & Fever blisters -

What are they? What's the difference between them? | How the herpes virus causes them. | HSV1 vs. HSV2. | What is Primary Herpetic Stomatitis?

Herpes virons
Link to Herpes Virus slideshow.

1) What is a cold sore?

A cold sore (sometimes referred to as a fever blister, see below) is a type of skin lesion caused by the herpes virus that either forms on a person's lips, or else on their face in the area immediately surrounding their mouth. These lesions generally have these characteristics.

Is there a difference between cold sores and fever blisters?

No, there's no difference at all. These are just two terms for exactly the same thing. They can be used interchangeably.

  • A person's outbreaks may correlate with periods of bodily stress caused by sickness (fevers or colds), hence the adoption of these names.
  • In scientific literature, these lesions are referred to as "recurrent herpes labialis."

The above term is easy to interpret when broken down into its component parts:

Recurrent = Occurring often or repeatedly.
Herpes = Refers to the Herpes virus, the causative agent of these lesions.
Labialis = Indicates that the sores form on or around the lips.

2) What causes cold sores / fever blisters?

The causative agent of these sores (not to be confused with factors that trigger actual outbreaks) is the herpes simplex virus. In most cases, however, it's not the type of "herpes" that you're probably thinking of right now.

There are actually two types of herpes virus. They are referred to as "type 1" and "type 2." Here's the difference between them.

Graphic stating most cold sores are caused by Herpes Simplex - Type 1.

Most cold sores are caused by Herpes Simplex - Type 1.

  • Herpes simplex virus - Type 1. (HSV1)

    Herpes type 1 generally only infects those body tissues that lie "above the waistline" and it's this virus that causes cold sores in the majority of cases.

  • Herpes simplex virus - Type 2. (HSV2)

    Herpes type 2 usually only infects those body tissues that lie "below the waistline." It's this version of the virus that's also referred to as "genital herpes." HSV2 is not usually the virus responsible for oral herpes lesions, although it's possible.

How do you get oral herpes?

The virus typically enters your body via a break in your skin (lips, skin around your mouth or the lining inside it).

3) The cold sores / herpes virus relationship.

The way the herpes virus causes cold sores isn't as straightforward as you might think. Here are the details.

a) You didn't just "get" the herpes that caused your cold sore, you all ready had it.

Sideshow showing images of herpes simplex virions.

The herpes simplex virus.

When you think of having an infection, you usually assume that you were recently exposed to the germ that's caused your problem. With cold sores however, that's not the case.


Cold sores are not a sign of a recently acquired herpes simplex infection but instead a reactivation of virus particles (virions) already living inside your body. A sore forms when herpes virions, which have been lying dormant ("asleep"), become active again.

b) Where do these dormant virus particles come from?

The dormant virions come from a previous infection.

Primary herpetic stomatitis.

A person's initial oral herpes infection, termed "primary herpetic stomatitis," does not usually take the form of a cold sore (see below). And for this reason, a person may not relate their initial exposure to herpes with the recurrent lip and facial sores they get later on.

Herpes is common and permanent.

Primary HSV1 infections are typically experienced before the age of 20 years. And most of us have one (80% of adolescents have antibodies for HSV1, a sign of having been exposed to it). (Opstelten 2008) [page references]

And once your first exposure has occurred, the virus remains inside your body (active or dormant) for the rest of your life.


4) The initial infection: Primary herpetic stomatitis.

a) What are the signs and symptoms?

The signs and symptoms associated with a person's initial infection of the herpes simplex virus (termed "primary herpetic stomatitis") usually take the following form:

  • The first signs of the infection are characterized by nonspecific symptoms. They can include: fever, irritability, headache, sore throat and swollen neck glands.
  • A day or so after the infection's initial signs have appeared, the person's mouth becomes painful and their gums become intensely inflamed (red, swollen, irritated).
  • Usually by day three of the infection, a number of tiny blisters have formed throughout the person's oral cavity (both in the front of and around the mouth, on the tongue, on the lips).
  • These blisters soon rupture and transform into gray colored ulcers (2 to 10 mm).
  • The ulcers can be very painful. They often interfere with the person's ability to eat.
  • Gradually, the ulcers begin to heal. Usually the entire infection has run its course in 10 to 14 days.
b) Why don't the symptoms of primary herpetic stomatitis seem familiar to you?
  • You were very young. - If you don't remember having had the classic signs and symptoms mentioned above it might be because you experienced them as a small child. Most cases occur before the age of 7.
  • Your case was very mild. - It can be that you don't remember going through this experience because your case was subclinical. This is by far the more common explanation.

    It's been estimated that between 90 and 99% of all cases of primary herpetic stomatitis are subclinical, meaning that the course of the infection was so slight that its symptoms were not readily apparent.

5) How common is having the herpes simplex virus (HSV1)?

The bad news.

As mentioned above, it's been estimated that roughly 80% of the general population has herpes simplex virus (HSV1) antibodies in their blood. Antibodies are proof positive that a person has been exposed because our immune system only creates them in response to the physical presence of virions within our bodies.

The good news.

The good news, at least from a statistical standpoint, is that although most of us have been infected with herpes type 1, it only causes outbreaks (cold sores / fever blisters) in about one third of the general population.

The rest of us do still carry the virus but, for whatever reasons, it remains dormant and we remain cold-sore free.

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General characteristics of cold sores / fever blisters.

We have other pages that go into much greater detail about lesion characteristics and management. Use these links as the jumping off point for the information you need.

  • Any one sore starts off as a group of tiny blisters that then rupture and combine to form a larger ulceration, which then scabs over as it heals. (The 5 stages of cold sore formation and healing.)
  • Cold sores frequently reappear, repeatedly. Usually in the same general location. Typically in response to some type of outbreak trigger.
  • While there's no "cure" for cold sores, they can be managed using a number of different prescription, OTC (non-prescription) and home-remedy solutions.

    These lesions are self-limiting however (they'll ultimately heal on their own), so some people seek no treatment.



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