Cold sores are notoriously difficult to treat - even Hollywood stars Katie Holmes and Lindsay Lohan, with their considerable resources, haven't managed to find a successful treatment for theirs.
Often the butt of juvenile sniggering because of their unjustified association with sex and STDs, cold sores are in fact a fairly common but undiscussed illness.
And far from being a subject of humour, the unsightly blistering can bring untold misery, affecting sufferers' physical and psychological health. Ballymena mum-of-two, Eve Marrs had them for 40 years.
"As soon as one cleared up, another would appear," says Eve (63). "They'd leave red scars. They were quite serious and nasty-looking - no-one wants to be seen with cold sores and you have to be careful not to pass them on to others, so extra care has to be taken using cups, cutlery and so on.
"When they begin to erupt, lipstick has to be avoided and being careful with face flannels and towels is a necessity. It really is embarrassing when they appear."
An education behavioural assistant, Eve first developed the herpes simplex virus HSV1 in her twenties. The strain causes cold sores, while an entirely different one, HSV2, causes genital warts. HSV1 cold sores periodically affect 33% of the population. The virus is silently carried by an estimated 85% of the population and can be reactivated at any time.
"I think they came because I was run down," Eve recalls. "I was already married to my husband Desmond when they appeared and had two young sons. If there was anything special coming up, you could guarantee they'd flare up. I could dress up and look smart, but I'd have this huge blister on my lip - always the top one.
"I couldn't cover them with lipstick because I didn't want to reinfect the area. I just put on creams; I even tried putting after shave and perfume on them to try and kill them. Absolutely nothing worked. I felt so self-conscious."
Eve stayed at home to bring up her sons Gary (38) and Ryan (33) before going out to work at children's play groups. When her cold sores worsened, she went to see her GP.
She says: "He recommended a well-known cream, but it was no use. I felt the tingle again in no time - it was very disappointing. I thought I was never going to get rid of them but I looked online last year and found a brand called Lipivir, and was able to get a free sample.
"I didn't expect a miracle but I thought, 'Why not try it?'. I'm very glad I did."
Lipivir is made by an innovative Swiss firm, Devirex. A lemon-scented liquid gel, it contains polyethylene glycols chemicals to prevent the eruption of blistering, rather than treat the notoriously stubborn virus. The gel is light and free from the common side effects of other topical products.
"When I put it on, it took the itch away immediately and the sore never reached the horrible crusty blister stage," Eve explains. "There was no sting or any side effects at all. To me, it was like magic - a Godsend. I just dabbed it on when the dreaded warning tingle began and it didn't get the chance to become a full blown cold sore.
"I can't really believe it myself, but after using it a few times I have now been totally free of cold sores for approximately eight months - that is a record for me."
Eve was delighted to discover that make-up, facial creams and cosmetic products can be worn on top of Lipivir, without causing undesirable results. For the first time in 40 years, she can wear her favourite lipstick as often as she wants.
"I like Max Factor's dusky pink. My cold sores were so visible, everyone noticed them. I know there's a stigma attached to them, but I was very lucky not to have been called names or anything. People understood.
"But now they're noticing my lipstick instead."
The highly visible nature of cold sores causes everything from embarrassment to shattered self-esteem and retreat from social involvement.
Its association with sexually transmitted diseases has been overstated; typically, all that's happened is the simple act of kissing when a cold sore is active. The facial eruptions can strike sufferers at times of stress, such as interviews, weddings and other public events, or can just appear out of the blue.
There are two types of herpes simplex virus - HSV1 and HSV2. HSV1 is what causes cold sores while HSV2 is generally the cause of genital herpes. According to estimates, about 80% of the world population carry HSV1.
A great many people acquire the cold sore virus in their childhood or during infancy. The cold sore virus is highly contagious - able to spread through skin-to-skin contact and in saliva.
The herpes simplex virus - sometimes called the cold sore virus - comes into types: HSV1 and HSV2. While the two variants have different DNA, both can cause oral and genital lesions or sores. The first type HSV1 is responsible for about 80% of oral herpes cases and only 20% of genital herpes. The HSV2 virus has the reverse proportions.
After the first incidence of cold sore, the virus retreats from the skin cells to the nerve cells - staying dormant there for years. However, all it takes is a trigger for the virus to reactivate and come back. Four of the most common cold sore triggers are catching a cold or flu, which depresses the body's immune system; exposure to intense sunlight; stress, which also weakens the body's defences; regular hormonal changes.
Swiss firm Devirex is marketing Lipivir as a light preventative gel which acts on the potential sore before it breaks the surface, making it the only product of its kind which focuses on prevention rather than treatment.
Lipivir is available online at www.lipivir.com, at a cost of £15 per tube which, if used twice a day, should last three months.
Users' reports of their experience of Lipivir are available online at http://forum.lipivir.com