These are caused by infection with the herpes simplex virus around the mouth.
The initial infection may cause no symptoms but the virus then remains dormant in the nerve tissue of the face.
However, in some people the virus reactivates and produces recurrent cold sores, usually in the same area, reports the Daily Mail .
Now, researchers at the Chicago Centre for Facial Plastic Surgery in the US are testing Botox as a treatment for the problem.
Men and women who suffer frequent outbreaks will be given an injection of the poison (which paralyses muscles) every three months for a year.
The theory is that Botox will block the reactivation of the virus by blocking the nerve where it lies dormant.
The doctors will take care not to put the Botox in the main muscle of the lip as this could affect movement.