How long does a cold sore generally last?

Two weeks. A cold sore is caused by a common virus-herpes simplex. They begin as a burning sensation in the lip area and this is followed by the formation of a blister. The blister ruptures and leaves a painful ulceration that then crusts over and heals within 10-14 days. There are some topical agents that can speed healing or abort the formation of the blister if caught early.