Reactivation of latent herpes virus has been linked to triggers of mild immunosupression, such as stress or UV-exposure. Despite having predictive value in severe immunodeficiency, the white blood cell (WBC) differential count has not been examined in relation to risk of herpes reactivation in population studies. The WBC differential count and other risk factors for herpes labialis were examined in 5687 adults (ages 18–64) from the Third National Health and Nutrition Examination Survey, who had WBC 3.5–11 × 106 cells mL−1 and reported no acute infections in the past month. The association between self-reported herpes labialis in the past year and the WBC differential count was modeled, adjusting for age, sex, race/ethnicity, education, smoking, upper respiratory infections (URI), and HSV-1 antibodies. Herpes labialis was significantly associated with white race/ethnicity, being a nonsmoker, and frequent URI. Compared with the highest quartile, being in the lowest quartile of granulocytes was associated with herpes labialis, adjusted odds ratio=1.82 (95% confidence interval 1.20, 2.28). At the same time, there was a trend towards an inverse association of lower lymphocyte count and herpes labialis. These findings suggest that moderate differences in the WBC differential count are related to reactivation of HSV-1. Prospective studies may help to show whether such differences indicate susceptibility to loss of latency or represent a consequence of reactivated infection.