Cold sores are caused a Herpes virus. You pick it up from someone through their infected saliva e.g. sharing a spoon or kissing. Once it reaches your skin it burrows in and sets up a nursery in any nearby nerve protecting its offspring from your immune system. Any that pop out quickly get nabbed by your fighter cells and killed.
Things change when you get stressed. Your immune system slows and the Herpes virus clan can then pop out the nerve and infect the skin above them. This is toxic to skin cells creating blisters.
The area of skin which is going to turn into a sore will burn, tingle and itch before you see it because the nerve gets irritated before the skin does.
There is no cure for cold sores because it hides dormant in nerves indefinitely. But when it tries to grow into a sore Acyclovir cream applied over the tingly area can drastically reduce an outbreak. Acyclovir looks alot like an ingredient Herpes uses when making copies of itself. But it's a dud so new copies don't work right.
If you get outbreaks very often your doctor may also put you on Acyclovir type tablets daily to lower your frequency of cold sores.
The key in cold sore treatment is to start Acyclovir cream or tabs at the first sign of symptoms.
