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10 Causes and Treatments for Cold Sores

Cause: Sunlight

Getting a little sun every day is a great way to stay healthy, including helping your body produce vitamin D. But for cold sores, the sun can be an unfortunate trigger.

Overexposure to ultraviolet rays from the sun can upset the tender skin on and around the lips. Even the slightest damage to the skin can trigger an outbreak of the virus, which typically lies dormant in nerve cells nearby [source: McKinley].

Keep this in mind the next time you're in the sun for prolonged time.