Docosanol is used to treat "cold sores/fever blisters" (herpes labialis). It can speed up healing of the sores and decrease symptoms (such as tingling, pain, burning, itching). It works by blocking the virus that causes the cold sores (herpes simplex) from entering the healthy skin cells and growing in number. This medication does not cure herpes and does not prevent passing the infection to someone else. It does not prevent a future occurrence. Do not use this medication to treat canker sores (sores found commonly in the mouth), shingles, or genital herpes.