cold sore illustration

What is a Cold Sore?

Also referred to as a fever blister, a cold sore is a group of blisters that form around the outside of the mouth and lips. They can be triggered by fatigue, stress, illness, pregnancy, exposure to sun or wind, dental work, or local skin irritation (such as a permanent cosmetic tattoo used to enhance the size or color of the lips).

Cold sores are fluid-filled lesions caused by herpes simplex virus type 1 infection.

For most, a cold sore starts with an early warning symptom - a tingling, itchy, or numb sensation at the location it will eventually erupt. Within a few minutes or hours, a small pimple-like bump appears. Within a day or two, the bump swells and is somewhat painful to the touch. A few days more, the swelling recedes, and transitions to a cluster of blisters. Another few days, the blisters burst open and eventually scab. The entire episode seems to never end, yet typically resolves in a couple of weeks.

Illustration courtesy of

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