What are cold sores?

Herpes labial, also known as fever blisters, are caused by two strains of the herpes simplex virus. Herpes simplex virus type 1 (HSV-1) is the main cause of oral and facial cold sores. HSV-2, which tends to affect the genitals, can also affect the mouth and face if it is transmitted there.

The cold sore virus is most often passed on through kissing - or oral sex - when a blister is present. You can get repeated outbreaks, although how severe and frequent these are can vary greatly.

Usually a small red mark appears, accompanied by a tingling, burning or itching sensation. This develops into a blister or a cluster of blisters which will eventually burst, leaving a raw area. The sore will heal without leaving a scar, typically within 7-10 days.

We talked to Professor Colm O'Mahony, a consultant in sexual health and patron of the Herpes Viruses Association (HVA), and uncovered some surprising insights about this common health issue:

Most people carry the virus, although some will never have obvious symptoms.

According to the World Health Organization, 67% of the global population are infected with HSV-1, the primary cause of cold sores - that's an estimated 3.7 billion people¹. However, not everyone with the virus will have repeating symptoms.

"One study showed that around 7 in 10 in people had antibodies to HSV-1 but fewer than 1 in 10 of them ever remembered having had a cold sore," says O'Mahony.

"It used to be that we lived in larger family units and communities that were in more close contact, so you would likely be exposed to the virus early in life. If you had a cold sore at two years old, you'd be infectious for two or three days. Then, your immune system would deal with it and you might never get a repeated outbreak, so you would forget about it - and grow up thinking you'd never had one and didn't have the virus."

Whether you are susceptible to repeated cold sore outbreaks, or carry the virus but never have symptoms, can be down to genes, reveals O'Mahony.

"Once you've contracted the virus, your likelihood of getting symptoms is 99% inherited," he explains. "Often, families carry a gene that makes cold sores more likely, and they will all be more susceptible. Everybody's immune system is different, one person's might be brilliant at dealing with cancer cells, but not much good with this virus; it's down to the particular immune response you inherit."

After the first infection, the herpes virus travels along a nerve pathway to the base of brain. It remains here, causing no symptoms, until triggered to multiply and travel back up the nerve - often causing a cold sore in exactly the same spot.

"Sunlight and UV light from sunbeds are a huge trigger," says O'Mahony. "Always use a high protection sunblock and avoid being out in the sun for too long. Any big change in the weather can do it though - we see a lot of cold sores when it suddenly gets cold at the beginning of winter."

According to the HVA, other common reasons for repeated outbreaks include stress, illness, alcohol and having a period - although O'Mahony suggests there is no evidence for an increased risk with hormone fluctuations, the contraceptive pill, or pregnancy.

Cold sores are mainly caught by direct skin contact with the affected area or through saliva. There is a slight risk of contracting the virus from saliva through sharing cups, cutlery, towels or lip salve. After contracting the virus, a cold sore is likely to appear after 4-6 days, although it may take up to two weeks for symptoms to occur.

Nigel Scott, trustee and former information officer at the HVA, suggests that in some cases, it can take years for the first obvious outbreak to occur. "About a third of people infected will show obvious symptoms quickly, but most will remain undiagnosed.

"A person might get minor symptoms such as a tingle, soreness or what seems like a cut lip that goes unnoticed. Then if something triggers the virus and they get a full cold sore years later, they are puzzled as to where they got it from because they had actually contracted it years earlier."

It is highly unlikely but not impossible that the virus can be spread from someone when they don't have a cold sore. This is called asymptomatic shedding.

"There has been so much hype about asymptomatic shedding that just causes needless worry," says O'Mahony. "The risk of passing the virus from one person to the next is extremely small. Most transmissions occur from an oozing cold sore, though it's important to avoid contact with people from the first sign of a tingle until after your skin has fully healed."

You can catch the virus on other parts of your skin, such as the hand and fingers, if you have broken skin there (known as a whitlow on the fingers). In rare cases, a cold sore can be serious. For example, a facial cold sore may affect the eye and this requires urgent medical attention. If you have an active cold sore, be careful not to touch it and then rub your eye.

A herpes virus may have implications in pregnancy and can be dangerous to newborns. So, if you have a cold sore never kiss a baby, and wash your hands before skin contact.

"A study we did showed that around 70% of women with genital herpes have HSV-1, indicating they are likely to have contracted the virus through receiving oral sex from a partner with a cold sore," says O'Mahony.

We tend to assume that oral sex carries less risk in terms of contracting infections, but many women with herpes genital will contract it this way

"There is less risk of transmission from mouth to genitals from someone who doesn't have an active cold sore," reassures O'Mahony. Just make sure that if your partner gets cold sores they are aware of the signs of an impending outbreak - tingling, redness, soreness - and avoid receiving oral sex during this time.

Antiviral creams containing aciclovir are widely available to purchase at pharmacies. If used at the tingle symptom stage, they can shorten outbreaks by 12%.

Antiviral tablets (aciclovir) can be prescribed by your GP and taken at the first sign of an outbreak, or more regularly as a preventative measure by those who experience frequent outbreaks.

1. World Health Organization: Herpes symplex virus.