Dr Clare Morrison

Article by Dr Clare Morrison

Getting on top of the cold sore virus

Cold sores are caused by a very common virus known as the herpes simplex virus (HSV). There are two types of HSV; HSV-1 and HSV-2. These two types are very similar, but usually infect different areas of the body. HSV-1 mostly infects the lips and mouth, causing cold sores. HSV-2 mostly infects the genitals and anus, causing genital herpes.1

In 2012 it was estimated that 67% of the world’s population (3.7 billion people) were infected with HSV-1. Most of these infections occur at a young age and once someone is infected, they will have the virus for life. Most infected people will never know that are infected as they will never develop symptoms, this is called being ‘asymptomatic’.1

Why do you get cold sores?

Your body’s immune system will usually keep HSV-1 infection under control, meaning you won’t develop symptoms. Only some people infected with HSV-1 will develop cold sores. This can be due to a short-term weakening of the immune system, caused for example, by illness or stress. But some people are just more prone to developing cold sores than others.1

Generally speaking, cold sores are low risk and are likely to pass with treatment or may pass on their own. In very occasional scenarios, cold sores can cause more serious complications, this is usually in someone with a damaged or permanently weakened immune system such as a person living with HIV.1

How do you catch cold sores?

Cold sores are typically passed between children through oral contact, where someone comes into contact with saliva or a blister from an infected person – this could be as simple as drinking from a shared bottle. The best way to avoid passing the herpes virus between people is to avoid oral contact and regularly wash your hands.

Genital herpes and cold sores – the herpes simplex virus

HSV also causes genital herpes. This is very similar to cold sores except the site of infection is the genitals or anus. Cold sores are usually caused by HSV-1 but genital herpes is usually caused by HSV-2.

Genital herpes is usually transmitted by genital to genital contact between an infected person and an uninfected person and as such, mostly occurs in adults.

In 2012, it was estimated that 417 million people were living with HSV-2 infection worldwide. The infection is also known to be more common in women than men, as the virus finds it easier to infect women.1

As with cold sores, most people with HSV-2 infection are unaware that they are infected and have no symptoms.1

In those people who develop symptoms, they will generally experience painful red spots and blisters (sometimes called ulcers) around their genitals.1


• There are two types of herpes simplex virus; HSV-1 and HSV-2 which are very similar but usually cause different conditions1

• In 2012, it was estimated that 3.7 billion people (67% of the world’s population) were infected with HSV-1, the virus which causes cold sores1

• In the same year, it was estimated that 417 million people were infected with HSV-2, the virus which causes genital herpes1

• For both cold sores and genital herpes, the greatest risk of transmitting the virus to someone else is when there are sores on the skin1

What is Aciclovir?

Aciclovir (sometimes spelt acyclovir) is a medicine known as an ‘antiviral’ because it acts to control viruses. Aciclovir is specifically designed to control HSV-1 and HSV-2 and for that reason is prescribed to treat both cold sores and genital herpes.2

HSV, like all viruses, has to make copies of itself to survive and infect new people. It does this inside human cells by hijacking parts of the human cell to make copies of itself. This includes copying its own genetic material (viral DNA). Aciclovir interrupts this process by stopping HSV from copying its viral DNA, preventing it from copying itself successfully.2

Aciclovir tablets in the UK

Aciclovir is a prescription only medicine in the UK, meaning you can’t get it at a highstreet

pharmacy without a prescription.2

MedExpress is an online doctor and pharmacy service that can give suitable people access to aciclovir following an online consultation. This means you can get a prescription for aciclovir for either cold sores or genital herpes online and receive your medicine in the post.

Click here to begin: https://www.medexpress.co.uk/clinics/sexual-health/genitalherpes/aciclovir


1. World Health Organisation. Herpes Simplex Virus. Fact Sheet. Available online: https://www.who.int/news-room/fact-sheets/detail/herpes-simplex-virus | Accessed March 2019.

2. Aciclovir. Summary of Product Characteristics. Electronic Medicines Compendium. Available at: https://www.medicines.org.uk/emc/product/4334/smpcAccessed March 2019.

Dr Clare Morrison
Dr Clare Morrison
Experienced General Practitioner in Hampshire since 1995, with particular interest in Nutrition, Obesity and Smoking Cessation.
Originally published April 23 2019, updated May 10 2019