Susceptibility to herpes labialis following multiple experimental exposures to ultraviolet radiation

We studied susceptibility to herpes labialis by exposing 20 volunteers to experimental ultraviolet radiation (UVR) on three occasions at 3- to 4-month intervals. The number of patients who developed lesions after each session was 9/20 (45%), 9/20 (45%) and 14/20 (70%). Herpes simplex virus (HSV) was isolated from 21/29 (72%) of lesions sampled. Three patients never developed a lesion, 13 developed lesions on one or two of the three occasions, and 4 patients had a lesion following all three sessions. Seven of 33 (21%) lesions were 'immediate' lesions (developed within 48 h) and the others developed 3-7 days after UVR exposure (delayed lesions). Development of lesions correlated with historical susceptibility to sun-induced herpes labialis, but not with age, sex, years with herpes labialis, frequency of herpes labialis from all causes, or concurrent serum levels of cortisol, dehydroepiandrosterone, estradiol, progesterone or alpha 1-antitrypsin. Among normally menstruating females, a significant association was identified between the development of herpes labialis and the luteal phase of the menstrual cycle (8 cases of herpes labialis/11 attempts, RR = 14, P = 0.005). The lack of correlation between episodes of natural herpes labialis and susceptibility to experimental UVR-induced disease suggests that these events are controlled differently. The results of serial attempts to induce experimental herpes in each patient was most commonly inconsistent, indicating that individual patient susceptibility to UVR varies over time. While the explanation for this variation remains unclear, stages of the menstrual cycle may be important among women.