Why is the cold sore virus life-threatening for some people?

Baby died in hospital after contracting common cold sore virus days after her birth

Cold sores are small, blister-like lesions that usually appear around the mouth. In most cases they are caused by herpes simplex viruses – the strain that usually causes them around the mouth is herpes simplex type 1.

Their persistence and ability to cause acute and sometimes life-threatening complications can arise with people whose immune system is compromised – especially in hospital settings – or when infection occurs in young babies. The virus can be difficult to treat and eradicate in such circumstances.

These were factors that arose in the case of a 12-day-old baby Eibhlín Wills who died at the National Maternity Hospital in Dublin after contracting the common cold sore virus in hospital days after her birth. Blood tests had shown no sign of the infection three days after birth, but infection was present in samples taken at five days.

Consultant virologist and director of UCD National Virus Reference Laboratory Prof Cillian De Gascun, who gave evidence at the inquest, summed up the particular difficulty with cold sores: "The challenge with herpes is you can actually transmit the virus without having a cold sore. In a significant proportion of cases, there won't be a cold sore and it's passed on as it asymptomatic."


The herpes simplex virus is highly contagious and can be easily passed from person to person by close direct contact. Once someone has been exposed to the virus, it remains dormant (inactive) most of the time.

However, every so often the virus is activated by certain triggers, causing an outbreak of cold sores, according to the HSE public health experts. The triggers that cause cold sores vary from person to person. Some people have frequently recurring cold sores, two to three times a year for example, while others have one cold sore and never have another. Some people never get cold sores because the virus never becomes active. They usually clear up without treatment in 7 to 10 days and do not leave a scar.

Creams and treatments are available over the counter that may help ease symptoms and speed up healing time. To be effective, these treatments must be applied as soon as there are signs of a cold sore, such as a burning or tingling sensation. In most cases, cold sores are mild.

Risk for babies

In newborn babies or people with weakened immune systems, such as those with cancer, cold sores can be life-threatening, although this is rare, explained Dr Kevin Kelleher, public health and child health director with the Health Protection Surveillance Centre (HPSC).

“Herpes is something that can be bagatelle for you or me but can be a very serious issue for others,” he added.

Neonatal herpes is not a formally notifiable disease, so it is difficult to get an exact indication of its prevalence. The coroner in the case of Eibhlín Wills recommended it should be a notifiable disease.

Dr Kelleher confirmed the HPSC last December recommended to the Department of Health that it be a notifiable disease – its decision was awaited.

Hospitals across Ireland, especially in acute settings and maternity units, have to be constantly vigilant because of a high incidence of hospital-acquired infections from a range of bacteria and viruses including herpes – the former are frequently resistant to a range of antibiotics.

Staff receive on-going training to prevent cross-contamination in hospital settings, especially where the immune system of a patient may be weakened due to other factors. In the case of a cold sore, once visible it should be immediately covered.

It is not possible to completely prevent what are known as “primary infections” or outbreaks of cold sores. They are at their most contagious when they burst (rupture), but remain contagious until they are completely healed. Therefore, it is important for other people to avoid direct contact with your affected area until your cold sore has completely healed and disappeared.

Spread of infection

Minimising spread and recurrence of cold sores can be achieved by:

– Avoid touching your cold sores unless you are applying a cream. Creams should be dabbed on gently rather than rubbed in as this can damage your skin further.

– Always wash your hands before and after applying cream and after touching the affected area.

– Do not share creams or medications with other people because this can cause the infection to spread.

– Do not share items that come into contact with the affected area, such as lipsticks or cutlery.

– Avoid kissing and oral sex until your cold sores have completely healed.

– If you have a cold sore, be particularly careful around newborn babies, pregnant women and people with a low immune system, such as people having chemotherapy or with HIV.

Preventing recurrent outbreaks

“If you know what usually triggers your cold sores, try to avoid these triggers if possible. For example, a sun block lip balm (SPF 15 or higher) may help prevent cold sores triggered by bright sunlight,” the HSE advises.

Use an antiviral cold sore cream, such as Zovirax, as soon as you feel the tingling sensation that indicates a coming cold sore. However, there is no benefit in using an antiviral cream continuously to try to prevent future cold sores. They cannot cure the virus and will only be effective once the virus has been triggered.

A guide to cold sores is available at:

Kevin O'Sullivan

Kevin O'Sullivan

Kevin O'Sullivan is Environment and Science Editor and former editor of The Irish Times