You might want to be wary if your crush makes a move under the mistletoe this Christmas.
A scientist from the University of Cambridge warns having a “good snog” under the festive decoration could spread cold sores.
While a crusty lesion may put you off puckering up, only a third of people with the responsible virus suffer cold sores.
Others carry it “silently” in their saliva, he added.
The stress of gift buying, decorating and meal planning this Christmas could also “wake” dormant viruses, leaving would-be kissers particularly vulnerable.
What causes cold sores?
Cold sores are caused by the virus herpes simplex one. This is different from genital herpes, which is triggered by herpes simplex two.
Once infected, the virus stays with a sufferer for the rest of their life.
Whether we know it or not, seven in 10 of us are already infected with herpes simplex one.
“Herpes spreads via close contact so if you have a good snog under the mistletoe you will pass it on,” Dr Chris Smith, consultant virologist and head of the “Naked Scientists” at the University of Cambridge, told Yahoo UK.
Kissing someone with the infection will not activate it within you if you already carry herpes simplex one.
Those without cold sores, however, may want to be wary of who is on the other end of the mistletoe.
“There is a proportion of people who have the virus but are asymptomatic,” Dr Smith said.
“They may shed the virus in their saliva, passing it on despite having no lesion.”
While cold sores can spring up throughout the year, many suffer more in the cold, dark months.
“Shorter days leave people feeling depressed, which triggers stress and therefore cold sores,” Dr Smith said.
“There’s also the classic Christmas stress that leaves you with a cold sore in time for Christmas Day.”
Perhaps surprisingly, jetting off for a sunshine getaway this winter could also leave you with a lesion.
“People get sick of the cold weather, go on a winter holiday, lie on a beach, and the UV rays damage the skin and activate a cold sore,” Dr Smith said.
“Also, the stress of going through Heathrow and Stansted can’t be underestimated.”
How do cold sores spread?
Cold sores are not serious, but can be unsightly and painful.
To avoid passing the virus on, the NHS recommends shunning kissing, sharing cutlery and having oral sex the moment you feel the tell-tale tingle.
It is particularly important not to kiss newborn babies. Their immune system is not developed enough to fight the virus, which can lead to life-threatening neonatal herpes.
“The virus lives in the nervous system, where it lurks inactive in cells,” Dr Smith said.
“It chemically ‘listens’ so it knows when you’re run down and then triggers nerve cells to ‘turn on’ viral DNA, so lots of viruses are made and infect the skin, leading to cold sores.
“The pain and tingling that occurs before a cold sore breaks out is when the virus buds out of DNA into the skin.”
Over the next two days, a small fluid-filled blister usually develops around the lips but can appear anywhere on the face. The blister then bursts and crusts over into a scab.
From the first sensation of tingling to when the cold sore has completely healed, a sufferer is contagious.
How are cold sores treated?
The lesion usually heals by itself in 10 days. Pharmacies sell creams that ease the pain, while antiviral lotions can speed up recovery time.
These should be applied as soon as you feel tingling, with effectiveness being limited once the cold sore has formed.
Some also find relief from applying heat, like Herpotherm.
“Heat seems to help reduce the duration of symptoms and make it less painful,” Dr Smith said.
“Heat may activate cells in the skin to produce defence proteins, which make the skin harder to infect.
“There is limited data on this because it’s a new theory.”
The NHS recommends seeing a GP if a cold sore lasts longer than 10 days. Pregnant women, those with weak immune systems and children with signs of gingivostomatitis - an infection that leads to swollen gums and mouth sores - should also seek help.