They're pesky and affect about one in three people - but now Rotorua cold sore sufferers are getting the chance to be part of a trial to help develop a new treatment for the common ailment.
In one of the largest studies undertaken in New Zealand, researchers are looking at whether a New Zealand honey formulation will help treat cold sores.
Rotorua's Ranolf Pharmacy is one of several in the country taking part in the research - something the team leading it say is unique as people can take part by going to the pharmacy instead of having to go to a hospital or university.
Ranolf Pharmacy owner Charlotte Schimanski said the pharmacy got on board about four weeks ago and so far had about half a dozen people signed up to take part.
"It's a really good opportunity for people to take part in a really useful study."
The other benefit was being able to receive treatment free, as part of the study, she said.
"Cold sore treatments aren't cheap. Getting free product is quite a good incentive."
Because it is a blind study, participants don't know whether they are receiving a common treatment or the honey-based treatment.
She said with plans to have about 950 people take part across the country, it was a large study.
"The more people we get the better it is."
The study is being run by the Medical Research Institute of New Zealand and will compare a formulation of kanuka honey, against a common antiviral drug.
The team led by medical researcher Dr Alex Semprini will evaluate which treatment more quickly heals cold sores.
Dr Semprini said the study was based on preliminary data from a similar, smaller study in Dubai that showed positive effects.
"We wanted to take the research to a full randomised controlled trial and gain a definite answer."
He said the study was unusually large and would be running for another 12 to 18 months.
"It's an opportunity to put a new treatment approach to the test for a condition that is both permanent and often difficult to treat satisfactorily."
Dr Semprini said he hoped to have results in 18 months.