New NASA research has revealed that dormant viruses may reactivate during spaceflight. Scientists reported that herpes viruses have reactivated in some crews involved in the Space Shuttle and the International Space Station missions.

To study the physiological effect of spaceflight, Satish Mehta, from Johnson Space Center, and colleagues analyzed the saliva, urine, and blood samples collected from astronauts before, during, and after spaceflight.

They found that during spaceflight, secretion of stress hormones increases. Stress hormones such as adrenaline and cortisol are known to suppress the immune system.

Mehta and colleagues also found that the astronauts' immune cells, particularly those that normally eliminate and suppress viruses, tend to be less effective during spaceflight and even up to 60 days after that.

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