Cold sores are also called fever blisters; they are small blisters around the mouth and lips area. Cold sore skin is usually sore, red and swollen. The cause of cold sore is a virus called herpes simplex. Normally it is spread by sharing eating utensils, razors, kissing a person who is infected or touching the saliva of an infected person. Cold sores usually heal on its own after a few days, but if it causes pain and embarrassment, it can be treated with an antiseptic cream or gel. Benzalkonium chloride is a common ingredient used to treat cold sores. There is no cure for cold sores. Exposure to too much sunlight can cause cold sore to flare up.