Surprising facts everyone should know about cold sores

Cold sores, 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, although 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 commonly passed on through kissing (or oral sex) when a blister is present. Recurrent outbreaks are likely to occur, although severity and frequency of symptoms 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 bursts 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 at Chester Sexual Health, and a patron of the Herpes Viruses Association (HVA), and uncovered some surprising insights about this common health issue:

You probably have it

Most people carry the virus, although some will never exhibit 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 people. However, not everyone with the virus will have recurrent symptoms.

"One study showed that about 70% of people had antibodies to HSV-1 but less than 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 more touchy-feely, so you would likely be exposed to the virus early in life. If you had a cold sore at 2 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 recurrence, so you'd forget about it and grow up thinking you'd never had one and didn't have the virus."

Not everyone has symptoms

Whether you are susceptible to recurrent cold sores or carry the virus but are never symptomatic, 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 in families the genetic predisposition is such that 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 just the particular immune response you inherited."

The weather can kick-start a cold sore

After initial infection, the herpes virus travels along a nerve pathway and resides in the ganglia at the base of brain, where it remains latent 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 prolonged exposure. 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 recurrences 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.

Transmission is only by direct skin contact

Cold sores are only caught by direct skin contact with the affected area. Contrary to popular belief, there is virtually no risk of contracting the virus 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, 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 those infected will show obvious symptoms quickly, but the majority will remain undiagnosed. They 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 the virus can be spread when a cold sore is not present (asymptomatic shedding).

"There has been so much hype about asymptomatic shedding that just causes needless worry," says O'Mahony. "The risk of transmission is infinitesimally small. Most transmission occurs from an oozing lesion, though it's important to avoid contact from the first sign of a tingle until after the skin has fully healed."

The virus can be caught on ordinary skin such as the hand/fingers if broken skin allows entry (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.

The 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.

Oral sex and cold sores shouldn't mix

"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 genital herpes will contract it this way

"There is virtually no 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.

Latest innovations in treatment and care

Antiviral creams containing aciclovir are widely available to purchase at chemists. If used at the 'tingle' stage, they can shorten outbreaks by 12%, and a newer antiviral cream, Fenestil®, contains penciclovir 1% and has a similar benefit. The HVA also lists Lomaherpan® cream as an effective alternative, which contains Melissa officinalis (lemon balm). In an HVA trial, 72% of participants said it prevented an outbreak from developing.

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 recurrences.

For more information visit the Herpes Viruses Association website.