Triggers for cold sore (fever blister) outbreaks. -

Known triggers. | How frequently do outbreaks occur? | What happens after the herpes virus becomes reactivated? | Why cold sores tend to recur in the same location.

Images of herpes simplex virions.

The herpes simplex virus.

What causes cold sore breakouts?

  • After a person's initial oral herpes infection (even a subclinical one) some virus particles (virions) will remain in their system, and will do so forever.
  • Most of the time, these virions will lie dormant and cause no apparent effects.
  • At times however, they can become activated. And once reactivation has been triggered, the person will experience a cold sore breakout.

What types of events can trigger outbreaks?

a) Common cold sore/fever blister triggers.

Systemic initiators -
  • Emotional upset or stress.
  • Physical stress and fatigue, including just being "run down."
  • Illnesses. This can include conditions like a cold, the flu or an upper respiratory infection.
  • Menstruation or pregnancy. For some women, cold sores are more frequent around the time of their monthly periods.
  • Immune system weakness or deficiency.
Local triggers -
  • Injury (physical trauma) to the lips or surrounding skin, such as a bite, scrape, cut or dermabrasion.
  • Exposure of the lips to bright sunlight, sunburn or an ultraviolet light source. Or extreme dryness, wind or cold exposure that results in chapping.
  • Dental treatment can act as a trigger for breakouts. This includes dental injections, periodontal procedures (gum work) and tooth extractions. So can other non-dental surgical procedures performed in the orofacial area.

(El Hayderi 2011) [page references]

b) How often do cold sore breakouts occur?

  • 5 to 10% of the general population experiences 6 or more outbreaks per year (Rooney 1993), with some people having as many as 12 or more (McCarthy 2012).
  • Most people probably have somewhere between "less than 2" (Rooney 1993) and 4 (McCarthy 2012) per year.
  • All told, somewhere between 16 to 38% of the general population suffers with these lesions. However, the number of cold sores that a person gets typically diminishes after the age of 35 years (Opstelten 2008). To the point where by their senior years, only 20% of people continue to experience them. (El Hayderi 2011)

c) Additional factors.

a) The cold-sore gene.

Some individuals may have a genetic susceptibility to getting cold sores. A paper by Kriesel, et. al. (2011) reported that their team identified a specific gene on chromosome 21 (gene C21orf91) as the likely source for this trait, although the mechanism by which it has its effect is not understood. They have given it the name Cold Sore Susceptibility Gene 1 (CSSG1).

b) Seasonality.

We decided to look for possible seasonal trends for when people tend to experience cold sores/fever blisters the most.

Our chart below shows how often people searched Google using the key words "cold sores." (We're making the assumption that few people have an interest in this topic unless they're looking for solutions for their own current problems.)

As you can see, this activity peaks during the winter months. That seems to make sense considering that it's a time of year when people are often stressed (such as from a hectic holiday season) or exposed to environmental conditions (cold, wind, dryness) that can result in lip chapping. (Both are known as triggers for sore formation.)

Graph showing monthly Google web searches for the term 'cold sores'.

Cold sore occurrence likely peaks during the winter months.

What happens after viral reactivation?

a) Background.

After a person's primary oral herpes infection, the virions recede, via the sensory nerve fibers servicing the affected area, to their corresponding ganglion. This is the location where the virus lies dormant.

(The one involved is usually the trigeminal ganglion. A ganglion is basically a hub of interconnected nerve fibers.)


b) Reactivation

The herpes virus lives in association with facial nerve fibers.

Animation showing the association of herpes virus particles and the face's nerve fibers.

When activated the virus forms a cold sore in the area the nerve services.

  • Frequently correlating with one of the triggering factors listed above, the dormant virus particles become activated. (The actual mechanism by which this takes place is not completely understood).
  • Once reactivation has occurred, the virus travels along nerve fibers from the ganglion to those areas of skin around the mouth that the fibers service.
  • The virus exits the nerve fibers and enters the neighboring skin cells where it starts to replicate (multiply).
  • As the number of virions increases, the infected skin cells ultimately die. This triggers an inflammation response in the surrounding tissues. And as this response unfolds, the cold sore passes through its 5 stages of formation.

(Hull 2014)

c) The components of herpes reactivation.

The process of virus reactivation is thought to be influenced by three component parts:

  1. The virus - This includes both the specific herpes strain as well as the number of virions residing in the ganglion.
  2. The triggering conditions - Factors include the relative severity of the event and the health status of the host at the time.
  3. Host genetics - As mentioned above, recent research suggests that a person's genetic makeup can influence their susceptibility to the reactivation process.

(Kriesel 2011)

Breakout periods often correlate with times of immune system stress.

It's thought that during "normal" times a person's immune system is able to keep the herpes virus in check. But when it's compromised (like during sickness) the virus is able to overcome body defenses and cause the formation of a lesion.

  • As you read through the list of known triggers above, it's easy enough to understand how some of them do correlate with time periods when a person's immune system is stressed.
  • Where as cold sores/fever blisters are typically just a nuisance for healthy individuals, they can be a serious matter (longer lasting more severe) for immunocompromised people (person's with a chronically debilitated or compromised immune system).

Locations where cold sores (fever blisters) form.

Animation showing the locations where cold sores form.

Why cold sores tend to recur in the same place.

The details above explain why cold sores tend to reoccur in the same general location. Here's a recap:

  • The herpes virus lives in association with specific nerves.
  • That means when virus reactivation is triggered and they travel back down the nerve, they're deposited in the same general location in the skin as with other outbreaks (see illustration).
  • Since a nerve ganglion (the location where the dormant virus resides) is a type of nerve "hub," it's possible that on some occasions the nerve fibers traveled are different than before. If so, the cold sore that forms that time will be in a slightly different location.
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Why you need to know about cold sore triggers.

Knowing when to expect a cold sore/fever blister is a very important part of managing them. That's because for best results it's imperative that any treatment is begun at the earliest sign of lesion formation.

[This goes for all types of treatments, not just prescription antivirals but also OTC products and home remedies too.]

By observing which factors typically trigger their cold sores, a person can learn when to anticipate an outbreak. And this may give them an opportunity to begin the use of medication early enough (preferably during the Tingle stage) that it can affect the course of their lesion and its symptoms, possibly significantly.



Topic Menu ▶  Cold Sores / Fever Blisters