Once you've got the herpes simplex virus, it's with you for life. All that you can do is to try to avoid the known triggers:
http://www.nhs.uk/Con...ore/Pages/Causes.aspx
You're also more likely to get cold sores if your general immunity level is low. That could come about, for example, from a deficiency of Vitamin D. (Well, that's what limited laboratory research suggests
might be true:
http://www.nhs.uk/new...he-immune-system.aspx )
More generally though, any poor diet is quite likely to lower your immunity levels.
Check the 'Treatment', 'Complications' and 'Prevention' links (from the first link above) for further information about cold sores.
Chris