Cold sores (fever blisters): What causes them? What is the herpes simplex virus?

What are cold sores?

Cold sores are a type of facial lesion that are found either on the lips or else on the skin in the area immediately adjacent to the mouth. Some equivalent terms that are used to refer to cold sores are "fever blisters" and the medical term "recurrent herpes labialis."

Specifically what causes cold sores?

Cold sores are caused by the herpes simplex virus. No doubt you've heard of "herpes" before, but don't jump ahead of yourself. There are actually two types of herpes simplex virus, "type 1" and "type 2."

Type 1 herpes simplex virus.

Herpes simplex virus type 1 ("HSV1") generally only infects those body tissues that lie "above the waistline" and it is HSV1 that causes cold sores in the majority of cases.

Type 2 herpes simplex virus.

Herpes simplex virus type 2 ("HSV2") usually only infects those body tissues that lie "below the waistline" and it is this virus that is also known as "genital herpes." Herpes simplex virus type 2 is not usually the virus that causes cold sores, although it can.

How do people get exposed to the herpes simplex virus that causes their cold sores?

When you think of having an infection you usually assume that you were recently exposed to the germ that has caused your problem. With cold sores this is not the case. Cold sores are not a sign of a recently acquired herpes simplex infection but instead a reactivation of herpes virus particles already living in your body. Cold sores occur when latent herpes simplex virus particles, which have been lying dormant ("asleep"), become reactivated.

Where does this dormant herpes simplex virus come from?

The dormant virus particles come from a previous herpes infection. A person's initial herpes simplex virus infection, termed "primary herpetic stomatitis," does not usually take the form of a cold sore and therefore a person may not relate their initial exposure to the herpes virus to the recurrent cold sores that they get.

What are the signs and symptoms of a person's initial herpes (HSV1) infection?

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 constitutional symptoms such as: fever, irritability, headache, and pain upon swallowing.
• A day or so after the infection's initial signs have appeared the person's mouth becomes painful and their gums become intensely inflamed.
• Usually by day three of the infection a number of tiny blisters have formed throughout the person's mouth.
• These blisters soon rupture resulting in gray colored ulcers.
• These ulcers can be very painful and often interfere with a person's ability to eat.
• The ulcers will eventually heal. Usually the entire infection has run its course within 10 to 14 days.

Why don't the symptoms of primary herpetic stomatitis seem familiar to you?

If you don't remember having had the classic signs and symptoms of primary herpetic stomatitis it might be because you experienced them as a small child. Most cases occur before the age of 7.

In other cases, if you don't remember having all the classic signs and symptoms, it's probably because your case was subclinical. This is by far the most common occurrence. It has been estimated that 99% of all cases of primary herpetic stomatitis are subclinical, meaning that the course the infection ran was so slight that its symptoms were not apparent. It is quite possible that when you had the infection that, at most, you only experienced one or two mild mouth sores.