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."