Spaceflight is hard on the human body. The absence of gravity can induce a form of nauseating motion sickness known as space adaptation syndrome. As time passes, weightlessness can also cause muscle wasting, bone deterioration, and other health problems.

NASA and its sister space agencies around the world have long recognized these health threats, and they’ve developed effective countermeasures. But as they’ve learned to manage the challenges of zero-gravity environments, other concerns have emerged.

According to a 2016 NASA-led study in the International Journal of General Medicine, time spent in space rapidly perturbs the human immune system. Nearly every molecule and marker of healthy immune operation — from the signaling activity of T cells to the production and action of cytokines — becomes dysregulated in space, and this dysregulation seems to contribute to a number of well-documented health problems, that study found.

To read more, click here.