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 virions
Link to Herpes Virus slideshow.

1) What is a cold sore?

Cold sores (sometimes referred to as fever blisters, see below) are a type of skin lesion caused by the herpes simplex virus that either form on a person's lips, or else on their face in the area immediately surrounding their mouth. (The lesions display these identifying characteristics.)

Is there any difference between cold sores and fever blisters?

No, there's no difference at all.

These two terms refer to exactly the same type of oral lesion and can be used interchangeably.

Where do these names come from?

It's common that a person's outbreaks correlate with periods of stress, like that caused by sickness (such as a fever or a cold), hence the use of those words in these terms.

Other terms.

In scientific literature, these lesions are referred to as "recurrent herpes labialis." This term is easy to interpret when it's broken down into its component parts:

Recurrent = Meaning something that occurs repeatedly in the same way.

Herpes = A reference to the herpesvirus, the causative agent of these lesions.

Labialis = Reference to the fact that these sores typically 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. But in most cases, what has caused your lesion is not the type of "herpes" that probably first comes to mind.


Multiple types of herpesviruses have been identified (8 types currently) but only two of them are associated with the formation of oral-facial lesions. They are the herpes simplex virus "type 1" and "type 2." Here are some primary differences 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 body tissues that lie "above the waistline," and primarily just those that compose the orofacial area.

    The tissues/regions most frequently affected are the intraoral mucosa (skin inside the mouth), the pharynx (the tissues lying just beyond the rear of the mouth), lips, eyes and skin above the waist.

    In the majority of cases, it's HSV1 that has caused a person's cold sore.

  • Herpes simplex virus - Type 2. (HSV2)

    Herpes type 2 is probably the form of the virus that first comes to a person's mind when herpes is mentioned. However, this type usually only infects those body tissues that lie "below the waistline" (specifically the genitals or skin below the waist).

    Because of that fact, HSV2 is not usually the form of the virus that causes oral lesions. However, in a small percentage of cases it has infected the oral-facial region and therefore be the responsible agent. (Lesions caused by either type of herpes are clinically indistinguishable.)


How do you get oral herpes?


It's generally considered that transmission of the herpes simplex virus occurs via direct contact with an infected individual (either their active lesion or saliva). We explain in greater detail here: HSV transmission.

Sideshow showing images of herpes simplex virions.

The herpes simplex virus.

Making entry into your body.
Once in contact with your skin, the herpes simplex virus binds to one of the cells making up its surface.
Then, an interaction between compounds found on the virus's surface (glycoproteins) and skin cell receptors facilitates the capsid's penetration into the cell. (The capsid is the portion of a virus particle that contains its genetic material, see photo viewer.)
The actual entry process involved can either be via membrane fusion (a joining of the membrane envelope of the virus and skin cell) or via a phagocytosis-like process where the membrane of the skin cell surrounds and "swallows up" (surrounds and engulfs) the virus particle. (Our photo viewer illustrates the latter process.)

Section references - Agelidis, Regezi, Neville

3) The cold sores / herpesvirus relationship.

The mechanism by which the herpes virus actually causes cold sores is probably substantially different than you'd expect. Here's how this (multi-step) process takes place.

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

When you think of having an infection, most people would logically just assume that they were recently exposed to the germs that have caused their problem. With cold sores however, that's not the situation.

Cold sores are a case of virus reactivation.
  • Getting a cold sore is not a sign that you've recently acquired a herpes simplex infection but instead, it's a sign of the reactivation of virus particles (virions) already living inside your body.
  • A sore forms when herpes virions, which have been lying dormant ("asleep") in your body, become active again (reactivate).


b) Where do the dormant virus particles come from?

The dormant virions come from a previous infection.

Primary herpetic stomatitis.

A person's previous (initial) oral herpes infection is termed "primary herpetic stomatitis," or alternatively "acute herpetic gingivostomatitis".

Most primary episodes do not take the form of a cold sore. And in fact, in most cases the person doesn't even display any significant symptoms at all (see below). Because of this:

  • Most people don't realize they've already had an exposure to the herpes simplex virus.
  • Or if they do, they don't make the correlation that that episode is related to the recurrent lip and facial sores they keep experiencing.


What you need to know is ...
Herpes is common, and permanent.
  • Primary HSV1 infections are typically experienced before the age of 20 years. (See statistics below.)
  • Most of us have had one. (80% of adolescents have antibodies for HSV1, a sign of having been exposed to it).
  • Once your first exposure has occurred, the virus remains inside your body (active or dormant) for the rest of your life.

Section references - Opstelten


4) The initial infection: Primary herpetic stomatitis.

a) What are the signs and symptoms?

The signs and symptoms of a person's initial infection of the herpes simplex virus ("primary herpetic stomatitis") usually involve the following characteristics:

  • The initial signs of the developing infection are only nonspecific in nature. They can include: fever (103 to 105 degrees F), nausea, irritability, headache, sore throat and/or swollen neck glands.

    (The incubation period following a person's exposure can range from 2 to 20 days, with cases that produce obvious symptoms often associated with an incubation period of 3 to 9 days.)

  • A day or so after the above signs have started to appear, the person's mouth becomes painful and their gums become intensely inflamed (red, swollen, irritated).


  • Usually by day three, a number of tiny, pinhead-sized (1 to 2mm) vesicles (blisters) have formed throughout the person's oral cavity.

    They may form on any oral mucosal (skin) surface, on the tongue, on the lips, or on the skin around the mouth. The number of blisters that actually form can be quite variable.

  • The blisters soon rupture, and tend to enlarge slightly as they transform into an ulcerated area that's covered over by a yellowish-grey pseudomembrane (2 mm or so in size). Individual ulcerations may coalesce (merge together) into larger, irregular-shaped lesions (as large as 10 mm).
  • The ulcers can be extremely painful. They often interfere with the person's ability to eat.
  • At this point, the ulcers will gradually start to heal. Mild cases may resolve in as little as 5 to 10 days. Severe cases may last up to 2 weeks.


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.

    When affected, most individuals are between the ages of 6 months and 5 years, with most cases involving those between 2 and 3 years.

    Cases before the age of 6 months are rare due to the protection of maternal antibodies.

  • Previously unexposed adults can experience primary herpetic stomatitis at any age.

    After age 5, a second peak of incidence tends to occur in populations involving those in their early 20's. Cases have been reported with persons who are over 60 years in age.


Your case was very mild. - It can be that you don't remember going through this experience because your case was subclinical.

It's been estimated that between 90 and 99% of all cases of primary herpetic stomatitis are either asymptomatic, or so mild in nature that the episode goes unnoticed by the child or their parents.

Section references - Arduino, Regezi, Neville

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 (20 to 40%) 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.

Section references - Arduino

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 area of 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.

Section references - The textbooks by Regezi and Neville were used as primary reference sources for this entire page.


 Page references sources: 

Agelidis AM, et al. Cell entry mechanisms of HSV: What we have learned in recent years.

Arduino PG, et al. Herpes Simplex Virus Type 1 infection: Overview on relevant clinico-pathological features.

Neville BW, et al. Oral and Maxillofacial Pathology. Chapter: Viral Infections.

Opstelten W, et al. Treatment and prevention of herpes labialis.

Regezi JA, et al. Oral Pathology: Clinical Pathologic Correlations. Chapter: Vesiculobullous Diseases.

All reference sources for topic Dental Crowns.