woman looking at her lip at a potential cold sore

Cold sores: Getting under the skin of what causes a cold sore

Pimple or cold sore? To help you identify the difference, we explain what causes a cold sore in five simple facts.

It happened overnight. A red bump appeared on your face while you were sleeping. And it’s suspiciously close to your lips. And now all you can think of are two things. Firstly, is it a common pimple or a cold sore? And secondly, if it isn’t a spot, what has caused you to get a cold sore?

Here, we share five facts that will hopefully give you a helping hand in understanding what causes a cold sore. Because to keep them at bay, it's important to understand exactly what you're dealing with.

Fact #1: Cold sores are caused by a virus

Looks can be deceiving. Spots and cold sores look surprisingly similar when they very first emerge. However, beneath the surface, what causes a cold sore is very different.

Whereas a pimple is caused by a build-up of oil and dead skin cells clogging your pores, what causes a cold sore is a virus called herpes simplex. There are two herpes simplex viruses that cause skin infections - type 1 and type 21. Cold sores are a type 1 infection or HSV-1.

Fact #2: You’ll probably feel a cold sore coming before you see it

A tingling or burning sensation is a popular warning sign that you’re about to get a cold sore. This is known as the prodromal phase in the herpes simplex virus. Or in plain English, when you’re starting to experience symptoms ahead of the cold sore developing on the surface. In reality, it can be up to a couple of days after you feel this tingling before the cold sore actually arrives.

Fact #3: They tend to develop in specific places

Whereas acne can appear anywhere, cold sores most often appear somewhere on your face. In particular, these red, fluid-filled blisters tend to congregate on or around your lips and under your nose.2

Fact #4: They take one to two weeks to heal

The life cycle of a cold sore is longer than your average spot. You can expect most cold sores to start healing in 10 days3. In this time, it will move through the following stages:
  1. An itching, burning or tingling sensation around your lips signals that a cold sore is going to erupt within a day or two.
  2. A fluid-filled blister develops on the surface. It will be red and sore.
  3. If you have a cluster of blisters, they may merge together. And then eventually they burst. This leaves a shallow open sore that crusts over as it heals.

Fact #5: Cold sores are contagious

Are you wondering how do you get cold sores? The fact that the HSV-1 virus is very contagious makes it easy to catch and spread. So much so that you can pass on the virus even before you have any visible symptoms. And it remains contagious until the sore has completely healed. Spread is by close physical contact with skin or saliva. So, everything from kissing to sharing a towel can cause you to transmit the virus to someone else.

Is there a treatment for cold sores?

There are a whole range of cold sore treatments available both over-the-counter and on prescription (speak to your pharmacist or GP.) They can help reduce discomfort, offer protection to the skin as it heals, and maybe even shorten the life cycle of a breakout.  However, it’s important to remember that what causes a cold sore is a virus. And this can’t be cured with a treatment.

Although the sores themselves usually heal without a trace within two weeks, it’s not the end for the virus. Once you catch herpes simplex, it stays in your skin forever. Most of the time, it will be dormant and cause you no issues. But from time to time, the virus rouses again causing a cold sore to erupt. This often happens when you feel run down, stressed or under the weather.

But as with so many skin conditions, reactions to the HSV-1 virus vary significantly from person to person. In fact, it’s estimated that although about seven in ten people4 have caught the virus that cause cold sores, only one in three display symptoms (in the form of cold sores.) And if you do get them, it’s equally as unpredictable how often you’ll be affected. While the unlucky ones get cold sores every month, others will only ever get one cold sore after contracting the virus.

Last updated: 20 April 2020

  1. https://www.britishskinfoundation.org.uk/herpes-simplex
  2. https://www.healthline.com/health/skin-disorders/pimple-vs-cold-sore#preventing-cold-sores
  3. https://www.nhs.uk/conditions/cold-sores/
  4. https://herpes.org.uk/cold-sores/