Have you ever developed a cold sore after a period of stress at work or at home?
It's a reactivating herpes virus and the same thing happens to astronauts.
A new NASA study shows that more than half of astronauts returning from space are returning home with the reactivated herpes virus.
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They think that it is because of all the stress they are under: zero gravity, cosmic radiation and separation of loved ones.
The more they stay in space, the more viruses can reactivate.
There are many herpes viruses that cause diseases such as chicken pox, shingles, genital herpes and cold sores.
Once these pathogens are in your system, they never go away, they simply stay dormant and can wake up at any time.
Most astronauts showed no symptoms and their reactivated herpes virus was only detectable by medical tests.
Nevertheless, they could infect others and scientists worry about other negative health effects that could have an extended time in the space.