Cullins explains that the first, or initial, outbreak is usually the worst, and “over time when you have recurrent episodes, you may not have systemic symptoms” or frequent symptoms. But everyone’s body and immune system reacts to the virus differently; while some people may never have many outbreaks, other people may be more chronically symptomatic. The National Institutes of Health indicate that infrequent outbreaks, around one or two per year, are not uncommon.
The causes of reactivation are uncertain, but several potential triggers have been documented. A 2009 study showed the protein VP16 plays a key role in reactivation of the dormant virus. Changes in the immune system during menstruation may play a role in HSV-1 reactivation. Concurrent infections, such as viral upper respiratory tract infection or other febrile diseases, can cause outbreaks. Reactivation due to other infections is the likely source of the historic terms 'cold sore' and 'fever blister'.
A 2004 study in the New England Journal of Medicine found that suppressive therapy decreases the risk of HSV-2 transmission from symptomatic, infected partners to uninfected partners by 48%. So “the risk of transmission is significantly reduced, but cannot be eliminated even with suppressive therapy,” Johnston explains, and she stresses that the virus can be passed along even without signs or symptoms.