What Is a Cold Sore? A cold sore is a group of tiny, painful blisters caused by the herpes simplex virus (HSV). They’re also called fever blisters or herpes simplex labialis. Up to 90% of people around the world have at least one form of HSV. The symptoms are usually the most severe the first you time you get cold sores. A first-time cold sore can make a child seriously ill. After the first outbreak, your body should make antibodies, and you may never have another infection. But many people get cold sores that come back.

Cold Sore Symptoms Cold sores are most likely to show up on the outside of your mouth and lips, but you can also get them on your nose and cheeks. You may get cold sores as late as 20 days after you’re infected. The sore might appear near where the virus entered your body. Cold sores happen in stages: You have a tingling, burning, or itching feeling. About 12 to 24 hours later, blisters form. The area becomes red, swollen, and painful. The blisters break open, and fluid comes out. This usually lasts 2 or 3 days. A scab forms on the sore. It might crack or bleed. The scab falls off. You might also have red or swollen gums, swollen glands in your neck, fever, or muscle aches. First-time infections can also cause: Burning and pain inside your mouth

Sore throat

Pain when swallowing

Headache

Upset stomach