4. Cold sores
A cold sore isn’t actually caused by a cold virus, but a herpes virus. “Cold sores are recurrent,” says Brodie. “Once you’ve had one, the virus rests in a dormant state until it’s triggered again. Then it will reappear.” Common triggers for these blisters include stress, fatigue, fever, menstrual cycle changes and sun exposure. Most of the time, cold sores form on the lip and last one to two weeks. Numbing ointments will help while you wait for them to heal.
The biggest difference between cold sores and other common mouth sores: They’re highly contagious. “They can easily be spread to others,” says Brodie. “Special care has to be taken when kissing or wiping your hands on your mouth.” And don’t pick at them!