Cold sores (fever blisters)

Small, painful, fluid-filled blisters on the mouth or nose, cold sores are caused by the herpes simplex virus. Lasting about seven to 10 days, cold sores are contagious until completely crusted over. Triggers can include fever, too much sun, stress, or menstruation. Antiviral pills or creams can be used as treatment, but call your doctor if sores contain pus, you have a fever greater than 100.5°, or if your eyes become irritated.