Cold sores

A cold sore is a small blister filled with fluid that appears in or around your nose or mouth. It often starts with a tingling or burning feeling and then the sore appears. 

Cold sores are due to infection with the herpes simplex virus (HSV). There are 2 types of HSV:

• HSV-1 cold sores and genital herpes. 
• HSV-2 mainly causes genital herpes. Read more about genital herpes.

The virus is spread by skin to skin contact. It's possible to catch it indirectly through contact with saliva or other body fluids, but most people get it directly from another person who has an active sore. HSV-1 is so common that most people have cold sores before they get to 5 years of age. 

Once you have had a cold sore the virus remains in your nerves and can become active later causing another cold sore. 

The initial infection

When you're infected with the herpes simplex virus for the first time, the episode is called a primary infection or initial infection. It usually happens when you're a child from close contact (eg, kissing) with a relative who has the virus. It can take 1 to 3 weeks to show any symptoms.

The first infection can be so mild you don’t notice it, but it’s usually the hardest. It lasts for 10 to 14 days. You may have the following symptoms:

• Fever (high temperature) which lasts for 3 to 5 days.
• Many sores around your mouth, nose, gums, throat and palate (roof of your mouth).
• Eating can be painful.
• Bad breath.
• Tiredness.
• Tender, enlarged lymph nodes in your neck.
  
  

Image credit: Canva

The herpes simplex virus remains hidden in your nerves for the rest of your life. It can become active again from time to time causing a cold sore. This will usually show up in the same places where you‘ve had an infection before. Cold sores don’t usually come back more than once a year, but about 5 to 10% of people get 6 or more episodes a year.

The virus can be triggered to become active by a fever (eg, a common cold), menstruation, skin damage, UV radiation (exposure to sunlight), extreme tiredness or lowered immune function.

An outbreak

An outbreak has 4 stages:

• A tingling feeling in your skin.
• Over the next 48 hours, you may notice slight swelling of the area and then a group of of fluid-filled blisters come up, which are often painful.
• Over the next few days, the blisters burst and form clusters, leaving fluid-filled sores.
• After 8 to 10 days, the sores eventually dry, scab over and heal without scarring. This stage can be irritating and painful.

You're contagious (able to pass the virus on) from the moment you first feel tingling or other signs of a cold sore coming on until the cold sores are completely covered by dry scabs.

Cold sores are diagnosed by the way they feel and look. If you're not sure, you can make an appointment to see your healthcare provider while the sore is there. They can take a swab to send to the lab if there is any doubt.

If you have just 1 or 2 blisters on your lip or near your nose, keeping the blister clean, dry and leaving it alone is usually all that's needed. Here are some tips that can help with healing.

• Use sunblock lip balm (SPF 15 or above) if you’re outside in the sun.
• Cold sore (hydrocolloid) patches from your pharmacy can protect your skin while it heals.
• Ice, held against the blisters, or a warm wash cloth may help ease any pain.
• Avoid acidic or salty food if it makes your cold sore feel worse.
• Rinse your mouth with salt water or a pain relieving mouthwash.
• You can buy antiviral creams (penciclovir or aciclovir) from your pharmacy. Your outbreak might be shorter if you start using a cream when you first feel tingling. Read more about aciclovir cream.
• You can buy an antiviral treatment called famciclovir from your pharmacy. Read more about famciclovir tablets.
• A kanuka honey based cream called Honeva is also available and has been shown to be as effective as aciclovir for treating cold sores. 
• Take pain relief such as paracetamol or ibuprofen.
• If you use contact lenses make sure you wash your hands well before handling them – HSV can be dangerous in your eyes.

How can I avoid spreading cold sores to other people?

Hygiene is important for people infected with the herpes virus. To help prevent it spreading: 

• don't kiss anyone while you have a cold sore, especially babies
• don't share anything that comes into contact with a cold sore (such as cold sore creams, towels, cutlery or lipstick)
• wait to have oral sex until your cold sore completely heals as you could pass on genital herpes
• avoid touching your cold sores and if you do, wash your hands. 

See your healthcare provider if:

• the cold sore hasn't started to heal within 10 days
• you have an infection near your eye
• the cold sore is very large or painful
• you have swollen, painful gums and sores in your mouth (gingivostomatitis)
• your child isn't able to drink and you think they could be dehydrated
• you have a weakened immune system – for example, because of chemotherapy or diabetes.

If your cold sores are very large, painful or keep coming back, your healthcare provider may give you an antiviral treatment such as valaciclovir.

The herpes simplex virus remains hidden in your nerves for the rest of your life. It can become active again from time to time causing a cold sore. This will usually show up in the same places where you may have had a previous infection. Most people don't get more than one recurrence of cold sores per year, but about 5–10% of people experience 6 or more episodes per year. Situations that trigger the virus to become active include a fever (eg, a common cold), menstruation, trauma, UV radiation (exposure to sunlight), extreme tiredness or lowered immune function.