Table 2.

Summary of Space Hazards to each organ system and potential countermeasures.

Tread/Hazards	Health Risks	Current Countermeasure
Microgravity
Musculoskeletal	Muscle and bone atrophy [19]	A combination of adequate exercise and antiresorptive medications [20,21]
	Impaired wound healing [22,23,24]	No specific countermeasures exist
Neurology	Space motion sickness (SMS) [25]	Scopolamine administered orally or via transdermal patch with or without an amphetamine (to counteract drowsiness), or intramuscular Promethazine [26]
	Alterations of smell and taste [27]	No specific countermeasures exist
	Self-reported congestion [27]	Lower body negative pressure may help, but the effects are transient
	Internal jugular vein thrombosis [28,29]	No specific countermeasures exist
	Post-flight motion sickness [30]	No specific countermeasures exist
Immunology	Reactivation of latent viruses [31,32]	Preflight vaccination [32] Treatment with polyclonal immunoglobulin (IG) and Interleukin-2 (SC) [33] Adequate exercise and nutrition [33]
	Hypersensitivity [34]	No specific countermeasures exist
Gastroenterology	Gut microbiota dysbiosis [2]	Probiotics, synthetic peptides, synthetic biology [35,36,37,38]
	Acute appendicitis and cholecystitis	Inflight medical management or minimally invasive procedures (e.g., ultrasound guided percutaneous drainage) of traditionally “surgical” conditions. [39] Alternatively, can consider prophylactic minimally invasive surgery prior to prolonged space flight in at-risk individuals [40]
Cardiovascular	Orthostatic intolerance [41]	Regular exercise training and adequate hydration prior to landing
	Cardiac myocyte atrophy [42]	Restores back to baseline after returning from spaceflight
Ophthalmology	Spaceflight-Associated Neuro-Ocular Syndrome (SANS) [43]	The lower body negative pressure device has been proposed as a countermeasure but is currently unproven
Dermatology	Skin tinning, dry skin, delayed wound healing, or skin infections [44]	No specific countermeasures exist
Traumatology	Increased risk of traumatic injury with construction, inadvertent acceleration of large masses when in zero gravity, impaired physiologic responses to hemorrhage and shock in zero gravity, bone demineralization increases risk of traumatic fractures, micrometeorites in EVA activities [45,46,47]	No specific countermeasures exist
Radiation
Most systems	Cancer induction	Shielding, including advanced shielding options. [48,49] Optimize mission according to solar cycle [48,49] Sex- and age-based selection criteria for astronauts [48]
Musculoskeletal	Bone cell remodeling [6]	Shielding [7]
Hematology	Acute hematopoietic effects [7]	Shielding [7]
	Space-related hemolytic anemia [50,51]	Screening and monitoring for hemolysis
Neurology	Neuro-degenerative disorders and central nervous system changes [52,53,54,55,56]	Adaptive visuo-motor training, active sensory feedback to guide task performance, galvanic vestibular stimulation (GVS)
Gastroenterology	Gut microbiota dysbiosis [2]	Probiotics, synthetic peptides, synthetic biology [35,36,37,38]
Cardiovascular	Accelerated atherosclerosis [3,4,57,58,59,60]	Shielding [7]
Ophthalmology	Radiation-induced cataract [61,62]	No specific countermeasures exist
Pulmonology	Lung adenocarcinomas and squamous cell carcinomas [63]	Shielding [7]
Dermatology	Melanoma and non-melanoma skin cancers [44]	Inflight telediagnostic system
Others
Nutrition	Nutritional deficiencies [64]	Telehealth and routine lab work for identification of nutritional deficiencies, and adequate supplementation as needed
Mental health	Psychologic distress [10,65]	Stress-relieving breathing exercises and/or mindfulness/positive visualization exercises [66]
	Depression, confinement, isolation, immobilization lack of social interaction [10,65,67]	Telepsychiatry, telepsychotherapy, space social media using LunaNet [68,69,70].
Altered circadian rhythms	Circadian de-synchronization and sleep loss [71]	Melatonin supplementation may be useful [72]
Dust exposure	Extraterrestrial dust exposure [73]	No specific countermeasures exist
Auditory exposures	Noise generated from man-made sources such as mechanical equipment (Noise/sound does not propagate in the vacuum of space and it requires an atmosphere to propagate, e.g., the pressurized spacecraft interior) [74]	Hearing protection in the form of foam ear plugs [74]
Unknown infections	Mission-threatening risks from unknown infections or novel bacterial/viral phenotypes [75,76]	PPE and post-exposure quarantine [77]