This is an important question and hard to answer definitively. Some factors that have been studied include stress, poor diet, birth control pills, sunlight, menstruation and fatigue. However, there is no way of accurately predicting when the next outbreak will come. Keeping one's immune system strong is important. (Persons with weakened immune systems, such as HIV-positive individuals, have more frequent and severe outbreaks than HIV-negative persons.) Experts also recommend getting emotional support, as the psychological impact of genital herpes often is more upsetting than the physical symptoms.