Cold sores are caused by a virus known as Herpes Simplex Virus, usually type 1 - or HSV-1.
People usually become infected in childhood or adolescence when they are kissed by someone with the infection.
The virus may lay dormant for the rest of your life within the sensory nerves around your lips, but it can be reactivated at any time. Because the virus resides in the nerves, this explains the sensations you may feel, ranging from tingling to severe pain, during a cold sore outbreak.
One in five of us experience outbreaks at some time. Of those, some people experience only one or two cold sores in a lifetime, but a small number of people have outbreaks monthly or more frequently.
After you have caught the HSV-1 virus, a number of things can cause a flare-up, including colds, flu, upper respiratory tract infections or even accidentally injuring your lips. Even dental work or surgery may wake up the virus.
The weather can also be a trigger - people tend to suffer more from cold sores during periods of extreme weather, including cold and heat, sunshine and wind. And women have more chance of a cold sore outbreak just before menstruation.
If you have frequent cold sore outbreaks, you may be suffering from more chronic (long-term) conditions such as stress or fatigue. Take a look at your lifestyle and see if you can make some changes.
Many people who have a weakened immune system after or during a severe illness also suffer from recurrent outbreaks of cold sores.
Whatever the cause of your frequent flare-ups, outbreaks of cold sores can only make you feel worse.