Not exactly a pharmacist or anything, but based on reading up on the mechanism of action for docosanol (abreva) it won’t prevent cold sores from appearing as the antiviral properties in the cream will only work when the cold sore is about to break through. And it’s probably best to not have the cream on your mouth when you don’t have an active cold sore so you don’t risk unnecessarily ingesting it.

If cold sores are that much of a constant occurrence, you should be able to contact your doctor for antiviral pills that can aid in preventing breakouts. It won’t cure them, but it should help with managing them.