(CNN) - Have you ever developed a cold sore after a stressful time at work or home?
That’s herpes virus re-activating and the same thing happens to astronauts.
New NASA research shows more than half the astronauts who return from space come home with re-activated herpes viruses.
They think it’s because of all the stress they undergo like zero gravity, cosmic radiation and being separation from loved ones.
The longer they are in space, the more likely the viruses are to re-activate.
There are many different herpes viruses and they cause things like chicken pox, shingles, genital herpes and cold sores.
Once these pathogens are in your system, they never go away. They just go dormant and can wake up at any time.
Most of the astronauts didn’t show any symptoms and their re-activated herpes viruses were only detectable using medical tests.
Still, they could infect others and scientists worry about what other negative impacts on health could result from extended time in space.