Cold sores are small blisters that develop on the lips or around the mouth, caused by the herpes simplex virus (HSV-1) . Once you have the virus, it can lie dormant for long periods of time, but certain triggers can cause it to replicate and cause another cold sore. These triggers vary from person to person, but some common ones include:

• Exposure to hot sun or cold wind
• A cold or other illness
• Hormonal changes, such as those related to a menstrual period or pregnancy
• Stress, both physical and emotional
• Fatigue
• Fever and illness, such as cold or flu
• Damaged, dry or cracked lips

It can be hard to predict what triggers a cold sore, and they might seem to appear at the worst times. However, starting treatment as soon as you know you are developing a cold sore can promote healing and reduce the time it takes to heal. Antiviral medications may help, but they need to be started before day 3 or 4 of the blister formation.