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What causes cold sores?

Aysha

Medically reviewed on October 30, 2019

by Dr. Aysha Butt, Medical director

Dr. Aysha Butt is the Medical Director of FromMars, and is a GP Partner at Woodcote NHS Medical Practice.... read more

It’s back! A cold sore can creep up again when you thought you’d dealt with it last time. Sometimes not knowing what to do and how to get rid of it can be so frustrating. If you go online, there’s loads of advice. But it’s not always accurate.

That’s what we’re here for. We’re giving it to you straight.

What is a cold sore?

Cold sores are small blisters or sores that usually appear around the mouth at the edge of the lips, but they can also form on your chin, cheeks, inside your nose, and even in your mouth. They can itch and hurt, and the blisters often contain a fluid, which can crust over if the blisters burst, forming an area of hard, dry skin. Nice.

What causes cold sores?

There’s only one thing that causes cold sores, an infection by a herpes virus. There are different types of herpes virus, and the one which most often causes cold sores is called herpes simplex virus 1 (HSV-1). Cold sores can also be caused by the herpes virus which most often causes genital herpes too, herpes simplex virus 2 (HSV-2).

Herpes viruses usually spread through skin-to-skin contact. Someone with cold sores might touch their face and then touch you, or you could get the virus on your face by kissing someone with cold sores. Once the virus is on your skin, it finds its way into your body through convenient openings, like through cuts, or through orifices like your mouth. The virus then spreads through your skin cells, causing the blisters to form on the surface of your skin.

Unfortunately, once you’ve been infected by a herpes simplex virus, it stays with you for life. The virus works its way into the nerve cells in your skin, and it stays there for good. Your body can fight the virus when it's in your skin cells, but not when it’s in your nerves. Most of the time the virus stays dormant and you have no symptoms, but every now and then the virus reactivates and spreads out from the nerves into the surrounding skin cells, causing cold sores to form again. This occasional reactivation of the virus is called an outbreak or a flare up.

What can trigger a cold sore?

Cold sore flare ups usually happen around two or three times a year, but this can vary by person. They also tend to become less frequent as the years go by. How often you get a flare up can depend on your lifestyle, and even the weather, as cold sore outbreaks can be triggered by specific things. For instance, you’re more likely to get a flare up when your immune system isn’t firing on all cylinders, as your body will find it harder to suppress any outbreaks of the virus. Immune system cold sore triggers can include:

  • Illness. Other viral or bacterial infections, like colds and the flu, can tax your immune system and make flare ups more likely.
  • Stress. It doesn’t just affect you emotionally, stress can weaken your immune system too. That means that stress can cause your cold sores to return.
  • Fatigue. Feeling tired and run down can also weaken your immune system. Cold sores when run down are therefore always common.

Other things outside of your immune system can also cause flare ups as well, like:

  • The weather. Cold weather can trigger flare ups, as can exposure to strong sunlight.
  • Food. There’s a lot of advice online about what foods can trigger a cold sore flare up, but there’s little to no evidence to back any of this up, so take what you read with a pinch of salt. There might not be any hard science behind it, but you may feel that certain foods make flare ups more likely for you. Feel free to avoid these foods, especially when you feel stressed, run down, or ill.
  • Individual triggers for you. Some or all of the above triggers may give you a cold sore outbreak, but you may also have other triggers that are unique to you. Knowing what these are can be difficult to work out but paying attention to what you’re doing around the time outbreaks start might give you some ideas.

How to prevent spreading cold sores

Cold sores are contagious, and you can easily pass them on to others. To stop this from happening, try the following when you have a flare up:

  • First off, try not to touch the cold sores yourself, as if you rub and scratch at them, you can get the live virus on your fingers. If you touch someone else you can transfer the virus to them, or you can even transfer the virus to other parts of your body, like your genitals (don’t touch your cold sores and then go to the toilet!)
  • Wash your hands frequently, as it can be hard not to touch your cold sores. They can feel tight on your skin, they can itch and even hurt, and sometimes you find yourself touching them before you realise you’re even doing it. If you catch yourself touching your cold sores, wash your hands right away. Wash your hands often too, as you may not notice each time you touch your face.
  • Avoid sharing objects like mugs, glasses, toothbrushes, and towels, as although the virus can’t live for long when it’s away from the body, there is a chance it can be passed on by sharing objects.
  • Avoid skin-to-skin contact. Don’t kiss anyone when you have cold sores, and definitely don’t have oral sex, as there’s a chance your cold sores can give someone genital herpes. You may have to avoid contact sports too.
  • Use cold sore treatments. You can use prescription drugs like valaciclovir and Valtrex to help clear up outbreaks faster and to reduce the amount of time when you’re at your most contagious.

How to treat cold sores?

You can minimise the number of flare ups you have by knowing what your triggers are and by managing them. But sometimes outbreaks are unavoidable. No matter what you do occasionally the cold sores will return. So how do you treat these outbreaks to clear them up as fast as possible?

There are plenty of home remedies that have been suggested for cold sores, but these often have limited scientific evidence of how well they really work. While you can take pain killers to help deal with any discomfort, if you want to get rid of your cold sores faster, you could try prescription cold sore medications like valaciclovir and Valtrex. These treatments are anti-viral drugs which help your body fight the herpes virus during a flare up. These meds can also be prescribed as a daily suppressive treatment to lessen the chances of a herpes flare up happening in the first place.

So, now you have the information, it’s time to take action.