What is the active ingredient in over-the-counter Abreva?

The active ingredient in over-the-counter Abreva is docosanol, which is an antiviral medication that is used to treat cold sore infections caused by the herpes simplex virus, according to Drugs.com. Docosanol decreases healing time and the length of time symptoms are present.

Sufferers of cold sores should avoid close contact with other people when experiencing an outbreak as they are very contagious, advises Drugs.com. Abreva should not be shared with anyone because it can lead to spreading the infection further.

Side effects of docosanol are not common, but some users report headache or skin irritation at the site of application, reports Drugs.com.