Why do cold sores occur?

THAT'S THE WHY:In otherwise healthy people, cold sores may not be a serious condition, but they are undesirable to say the least.

Often painful and unsightly, they can be spread through contact and kissing, and those who develop them can have the misfortune of getting them repeatedly.

The blisters that crop up on the lip are usually caused by herpes simplex virus (HSV) type 1, and once you are infected, the virus travels to bunches of nerves called ganglia.

There it sits dormant until a trigger such as psychological stress, illness or even sunlight can result in it travelling back along the nervous system to wreak havoc on the skin again.

Our bodies can detect and develop immunity to many viruses, so why can this one persist and keep flaring up?

It’s because HSV-1 has a few tricks up its sleeve.

It uses an arsenal of molecular tricks to dodge the sight and wrath of our immune systems, including dampening down the activity of the cell it infects and going into a state of latency.

In a sense, it keeps the whole thing quiet while it is hiding, so the patrolling guards don’t pick up on it.

Some people may feel a warning, such as tingling, before a cold sore breaks out, giving them time to use anti-virals at an early stage and hopefully reduce the extent of the blister.