Prevention states that a cold sore should never be broken open deliberately. Cold sores are extremely contagious and should not be touched with an unprotected hand because of the danger of spreading the virus that causes them.
Cold sores are caused by a highly contagious virus. While they typically go away on their own within 10 to 14 days, anyone suffering from a cold sore should be careful not to spread it, according to Prevention. Touching the cold sore with an unprotected hand can spread the virus under the fingernails, causing further pain. Lip balm worn to protect against dry weather or sunshine should be applied with a cotton swab to prevent spreading the virus to the lip balm itself.