The thought of a single bug crawling over us while we sleep is bad enough. But hundreds of tiny blood-suckers that live, eat and reproduce right in the bed with you? That’s the stuff of nightmares.

An curved arrow pointing right. Dr. Melanie Grossman, a dermatologist based in New York City, explains what causes cold sores and how to prevent them. Follow BI Video: On Twitter More from Science Dr.

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Cold sores are painful blisters on the lips that can form unsightly crusts. They are very common and are caused by the herpes simplex virus. The medical name for facial cold sores is herpes labialis.

Bugs are surprisingly good at biting before you realize what’s happening. But by the time you feel that signature pinch or sting, they’ve often moved on. That can make it tough to know what ...