or reactivate? The truth is, no one knows for sure. A person doesn't necessarily have to
have a cold to
get a cold
sore — they can be brought on by other infections, fever, stress, sunlight, cold weather, hormone changes in menstruation or pregnancy, tooth extractions, and certain foods and drugs. In a lot of people, the cause is unpredictable.
Here's how a cold sore develops:
The herpes simplex virus-1, which has been lying dormant in the body, reactivates or "wakes up.