Astronauts who "boldly go where no man has gone before," as William Shatner's Captain Kirk once put it, likely anticipate their body will undergo certain changes while in space. But how many have guessed they might see a herpes flare-up? New research from NASA shows that the more time space explorers spend hovering above our planet, the higher the chances are that long-dormant herpes viruses—including chickenpox, shingles, and oral and genital herpes—will reactivate. In the study published in the Frontiers in Microbiology journal, about 53% of the 89 subjects who went on short space-shuttle flights, as well as 61% of the 23 space travelers who took longer-haul trips to the International Space Station, "shed" the herpes virus (meaning it reactivated) in their pee or saliva, lead author Satish Mehta says, per CNN.
And researchers believe stress is behind that reactivation, made possible since herpes viruses never completely disappear but merely lie dormant in immune and nerve cells, waiting to come back to life. Mehta notes that "during spaceflight there is a rise in secretion of stress hormones like cortisol and adrenaline, which are known to suppress the immune system," per the New York Post. One positive from the study: Just because the viruses reactivate doesn't mean their hosts will necessarily exhibit any signs, with Mehta noting only a handful of the study's subjects developed minor symptoms. However, those infected would still need to be cautious once they're back on terra firma to make sure they don't infect anyone with a compromised immune system. (Read more herpes stories.)