Fever blisters, also known as cold sores, are a common infection caused by herpes simplex viruses. They are fluid-filled and tiny spots around or on the lips or genitals. You often notice them in patches or groups. When the blisters break, they would form a crust over the affected area. In most cases, the condition often heals in a few weeks without a scar. This is a contagious issue that can spread from person to person through sexual or oral contact, even when you do not notice the sores. Since there is still no cure, they might return.