Hello Dr. My husband gets cold sore all of a sudden any time of the year on centre upper lip border. The duration varies from once a year 2-3 times a year. Whenever there is a outburst, He takes acivir dt 400 5 times a day with application of ointment at night as prescribed by a skin dr. 2 years ago. I would like to consult regarding this, is there a permanent treatment for this or how can this be avoided. Thanks.