Dermatologic Considerations for Spaceflight and Space Exploration

As of 2022, approximately 600 people have traveled to space, defined as reaching the Earth's orbit, including recently laypersons and tourists in addition to professional astronauts.[1NASA, Human Spaceflight.Google Scholar] As the space industry continues to expand into long-term space exploration including planned future missions back to the moon and to Mars,[2NASA, Mars Exploration.Google Scholar] it will be important for physicians to consider the known and potential health risks associated with space travel. This commentary covers space and health issues with a focus on dermatology, building on previous literature and conversations with experts, and providing guidance to clinicians who may be asked to support these endeavors.[3Arora S. Aerospace Dermatology. Indian J Dermatol. 2017; 62: 79-84Crossref PubMed Scopus (10) Google Scholar] We have grouped the dermatological issues as environmental risks, space wear, immunity, and radiation exposure related. Leaving the safety of the troposphere leads to a number of new environmental changes. When entering a microgravity environment, physiologic fluid equalization occurs. Notably, there is a shift of fluid out of the lower extremities towards the head. The impacts of fluid cephalization may cause facial edema and decreased fluid in the legs. Less visibly, the equalization of pressure may contribute to more fluid in venous plexuses which can lead to livedo reticularis-like change. These drastic fluid shifts can lead to swelling, discomfort, and increased skin irritation. Ultimately, there is a diuretic phenomenon that occurs with the re-distribution of fluid: upon entering a microgravity environment, the body will diurese approximately 2 liters of fluid. Prior literature has reported on hydration of the skin in a long-term mission in the International Space Station (ISS).[4Tronnier H. Wiebusch M. Heinrich U. Change in skin physiological parameters in space--report on and results of the first study on man.Skin Pharmacol Physiol. 2008; 21: 283-292Crossref PubMed Scopus (44) Google Scholar] Studies of hydration of the stratum corneum, transepidermal water loss, and surface structure of the skin were measured, showing that there may be delayed epidermal proliferation of cells and significant decrease in skin elasticity.[4Tronnier H. Wiebusch M. Heinrich U. Change in skin physiological parameters in space--report on and results of the first study on man.Skin Pharmacol Physiol. 2008; 21: 283-292Crossref PubMed Scopus (44) Google Scholar] Given that transepidermal water loss was increased during space travel and that transepidermal water loss is used to assess skin function and severity of diseases characterized by barrier dysfunction, such as atopic dermatitis, these observed space-related impacts on skin function are anticipated to contribute to challenges of skin barrier function in space. Further, the skin microbiome may experience alterations,[5Morrison M.D. et al.Investigation of Spaceflight Induced Changes to Astronaut Microbiomes.Front Microbiol. 2021; 12659179Crossref Scopus (28) Google Scholar, 6Voorhies A.A. et al.Study of the impact of long-duration space missions at the International Space Station on the astronaut microbiome.Sci Rep. 2019; 9: 9911Crossref PubMed Scopus (147) Google Scholar, 7Tozzo P. Delicati A. Caenazzo L. Skin Microbial Changes during Space Flights: A Systematic Review.Life (Basel). 2022; 12PubMed Google Scholar, 8Nguyen C.N. Urquieta E. Contemporary review of dermatologic conditions in space flight and future implications for long-duration exploration missions.Life Sci Space Res (Amst). 2023; 36: 147-156Crossref PubMed Scopus (0) Google Scholar] though studies have shown a lack of a consistent shift towards a "spaceflight" microbiome while on the ISS.[5Morrison M.D. et al.Investigation of Spaceflight Induced Changes to Astronaut Microbiomes.Front Microbiol. 2021; 12659179Crossref Scopus (28) Google Scholar] Potential changes to the skin microbiome pose hypothetical concerns for barrier dysfunction that translates to increased risk of infection and delays in the healing process.[9Caswell G. Eshelby B. Skin microbiome considerations for long haul space flights.Front Cell Dev Biol. 2022; 10956432Crossref PubMed Scopus (1) Google Scholar] It has been suggested that there may be issues related to astronaut attire. Notably, spacesuits are designed for the extreme temperatures and vacuum of space. Due to these environmental requirements, suits have been described as uncomfortable and not ergonomic. Beyond designs with incidentally associated discomfort, suits were historically designed for male astronauts. For women, these suits can be even less comfortable and more irritating. Further, astronauts routinely report injuries from spacesuit wear including pressure wounds in fingers, joints, and skin folds.10Aintablian, H., Interview conducted on medical considerations of space travel, M. Zhao, Editor. 2023.Google Scholar,11Satcher, R., Interview conducted on personal experiences in space, M. Zhao, Editor. 2023.Google Scholar Nail avulsion is not uncommon due to the combination of bulky suits, limited finger padding, and need for often prolonged manual dexterous maneuvers in space.10Aintablian, H., Interview conducted on medical considerations of space travel, M. Zhao, Editor. 2023.Google Scholar,11Satcher, R., Interview conducted on personal experiences in space, M. Zhao, Editor. 2023.Google Scholar Astronauts sometimes utilize adhesives to ensure skin-to-glove adherence during maneuvers, which can lead to skin damage and potential irritant or allergic contact dermatitis. Notably, NASA is designing and launching a new generation of space suits aimed to be more tailored to the astronaut, including sex-specific builds for female astronauts.[12Falconer, R., NASA reveals spacesuit for new Moon mission that better fits women, in Axios. 2023.Google Scholar] As space travel becomes increasingly more accessible to the public, it is important to realize how the diversity of body shapes with the misalignment of suit availability may lead to unintended irritation and injury. There appear to be alterations to the immune system in space, with ongoing studies aimed at better understanding the impacts.[13Malkani S. et al.Circulating miRNA Spaceflight Signature Reveals Targets for Countermeasure Development.Cell Rep. 2020; 33108448Abstract Full Text Full Text PDF Scopus (30) Google Scholar] There has been ongoing research looking at spaceflight-associated microRNA expression and its contribution to immune dysregulation in space. Studies have shown viral re-activation, such as Epstein Bar Virus (EBV) and Varicella Zoster Virus (VZV), including shingles).[6Voorhies A.A. et al.Study of the impact of long-duration space missions at the International Space Station on the astronaut microbiome.Sci Rep. 2019; 9: 9911Crossref PubMed Scopus (147) Google Scholar] Space travel can also lead to alterations in the microbiome. This may result in skin sensitivities with symptoms ranging from peeling, dryness, redness, itching, and bruising.[14Braun N. et al.Self-Reported Skin Changes by a Selected Number of Astronauts after Long-Duration Mission on ISS as Part of the Skin B Project.Skin Pharmacol Physiol. 2019; 32: 52-57Crossref PubMed Scopus (13) Google Scholar] The interaction of general gravitational forces with immunosuppression is an important topic to be considered.[9Caswell G. Eshelby B. Skin microbiome considerations for long haul space flights.Front Cell Dev Biol. 2022; 10956432Crossref PubMed Scopus (1) Google Scholar] Alterations to bone marrow and thymus have been described in association with gravitational forces, and may have impacts on acquired immunity[15Akiyama T. et al.How does spaceflight affect the acquired immune system?.NPJ Microgravity. 2020; 6: 14Crossref PubMed Scopus (60) Google Scholar] There is notable thymic atrophy and reduced T-cell output from space travel.[16Benjamin C.L. et al.Decreases in thymopoiesis of astronauts returning from space flight.JCI Insight. 2016; 1e88787Crossref Scopus (36) Google Scholar] Observations have also noted reduced B-cell count a week after landing[17Tascher G. et al.Analysis of femurs from mice embarked on board BION-M1 biosatellite reveals a decrease in immune cell development, including B cells, after 1 wk of recovery on Earth.FASEB J. 2019; 33: 3772-3783Crossref PubMed Scopus (27) Google Scholar]. Additional factors at play, including increased stress hormones during spaceflight, may further impact the immune response.[18Borchers A.T. Keen C.L. Gershwin M.E. Microgravity and immune responsiveness: implications for space travel.Nutrition. 2002; 18: 889-898Crossref PubMed Scopus (106) Google Scholar, 19Grover S. Skin in aviation and space environment.Indian J Dermatol Venereol Leprol. 2011; 77: 413-417Crossref PubMed Scopus (12) Google Scholar, 20Stowe R.P. Pierson D.L. Barrett A.D. Elevated stress hormone levels relate to Epstein-Barr virus reactivation in astronauts.Psychosom Med. 2001; 63: 891-895Crossref PubMed Scopus (118) Google Scholar] Exiting the protection of the ozone layer leads to increased potential radiation exposure. There are studies of airline pilots demonstrating increased risk of skin cancer, including melanoma, attributed to extended time at high altitudes and higher UV exposure.[21Sanlorenzo M. et al.The risk of melanoma in airline pilots and cabin crew: a meta-analysis.JAMA Dermatol. 2015; 151: 51-58Crossref PubMed Scopus (81) Google Scholar] Similarly, a study of 312 astronauts demonstrated a statistically significant 3-fold increase in prevalence of nonmelanoma skin cancers compared to non-astronauts.[22Institute of Medicine (US) Committee on the Longitudinal Study of Astronaut Health; Longnecker DE, M.F., Worth MH Jr., Review of NASA's Longitudinal Study of Astronaut Health. 2004.Google Scholar, 23Chancellor J.C. Scott G.B. Sutton J.P. Space Radiation: The Number One Risk to Astronaut Health beyond Low Earth Orbit.Life (Basel). 2014; 4: 491-510PubMed Google Scholar, 24Chancellor J.C. et al.Limitations in predicting the space radiation health risk for exploration astronauts.NPJ Microgravity. 2018; 4: 8Crossref PubMed Scopus (119) Google Scholar] Notably, the radiation types differ between flight pilots and astronauts. The radiation that affects astronauts is ionizing radiation, which includes galactic cosmic rays and solar events, whereas airline pilots remain within Earth's atmosphere and have increased exposure solely to UV radiation. As humans explore further into the solar system, astronauts will expectably spend prolonged periods of spaceflight beyond Earth's protective magnetic shield and incur increased exposure to different forms of radiation. As the space frontier continues to expand, it is important to keep up with the dermatologic considerations related to space travel. As physicians may become increasingly involved in the space industry, there will be increasing opportunities for physicians to advocate for the health of spaceflight participants. Fluid shifts, space wear, temperature and aridity, immune system, radiation exposure, and nutrition, impact dermatologic health and may require further management. As the final frontier, the skin is the largest skin-enviro interface organ. There is anticipation in identifying new and different cutaneous impacts of space travel on skin. It is important for dermatologists to be aware of, and involved in, these studies and to be aware of these findings. The effect of space travel on skin health and disease likely represents a nascent field of medical research and opportunity for dermatologists to be involved in the next steps of exploration.