Humans venturing into the environment of space can have negative effects on the body.[1] Significant adverse effects of long-term weightlessness include muscle atrophy and deterioration of the skeleton (spaceflight osteopenia).[2] Other significant effects include a slowing of cardiovascular system functions, decreased production of red blood cells, balance disorders, eyesight disorders and a weakening of the immune system. Additional symptoms include fluid redistribution (causing the "moon-face" appearance typical in pictures of astronauts experiencing weightlessness),[3][4] loss of body mass, nasal congestion, sleep disturbance, and excess flatulence.