What Causes Cold Sores?

Cold sores are caused by a common virus called the herpes simplex virus type 1. The herpes simplex virus is often passed on when you’re very young through physical contact like a kiss from a family member or friend who has it, but it lies dormant until it’s triggered at a later date. In some people it will just stay dormant and never cause any problems, but others develop cold sores.

Most people who have the herpes simplex virus will have come into contact with it between the ages of three and five - but the symptoms often don’t appear until after puberty.

In many cases, there’s no obvious reason for an outbreak of cold sores, but there are a few factors that are thought to make you more prone to a flare up. These include:

• If you have a cold or another infection of your respiratory tract - this can cause a temporary weakening of your body's defences which can lead to a reactivation of the virus and a new crop of blisters.
• If you’ve got a fever or high temperature
• If you’re dealing with stress or an emotional upset
• If you’re feeling tired or fatigued
• If you’ve injured the affected area
• If you’re having your period
• If you’ve been spending time in strong sunlight

Stress can only cause cold sores if you already have the herpes simplex virus.

When you’re stressed or even just feeling run down, this can affect your immune system. When your immune system is under pressure, the resistance to the virus isn’t as strong so the virus has a chance to break out again.

It’s not thought that there are any specific foods you can eat that will either cause cold sores or help you to avoid a break out. The general advice if you suffer from cold sores is to eat a healthy, balanced diet to strengthen your immune system.

Some people suggest that eating foods or taking supplements that contain the amino acid lysine could help to prevent and treat cold sores.

Allergies aren’t a known trigger for cold sores. 

The herpes simplex virus is commonly passed on through kissing someone who also has the virus, and as it’s very contagious, it’s best to avoid close physical contact with anyone who has cold sores.

Likewise, if you have cold sores yourself, avoid kissing anyone else until after the blisters have cleared up, to prevent passing the virus on.

Once you have the virus in your body there’s no cure for it, but there are some things you can do to avoid getting it in the first place and limit flare ups of cold sores if you do have it.

To prevent getting the virus, the number one thing you can do is avoid coming into close physical contact with anyone who has an active flare up.

Don’t share cutlery, cups or anything else that someone with cold sores might have used.

If you already have the herpes simplex virus

If you have the virus already and have had cold sores before, you can minimise the flare ups. If you experience frequent or severe outbreaks, your doctor may be able to prescribe antiviral medicines to take every day which prevent the cold sores from coming back.

Otherwise, you can try lifestyle changes that might help keep the blisters at bay.

Other things you can do include:

• Don’t touch the sores - however tempting, just leave them alone.
• Don’t pick the sores - they can become infected and you might transmit them to other areas of your body.
• Always wash your hands after touching your lips.
• Eat a varied diet, exercise regularly and get enough sleep so that you keep your immune system functioning well.
• Keep an eye on your triggers - some women find that their menstrual cycle can trigger an outbreak so have some cold sore medicine on hand for that first tingle if you know it’s something that sets yours off.
• Using sunblock can also help to prevent a flare up in some people.