Sexual Health in Space: a 5-year Scoping Review

The combined efforts of national and private space organizations are progressively allowing more people to live and work in space. But to perform long-term spaceflights and become a multiplanetary species, we must address the intimate and sexual needs of humans. Yet, research on space sexology remains limited and fragmented. To move forward, this 5-year scoping review consolidates the current research on sexual health in space. Fifty publications were identified, including empirical, theoretical, and review articles, and other scholarly work, such as book chapters and a commentary. Most of the research comes from biology, with contributions from philosophy, ethics, and law, gynecology/obstetrics, aerospace medicine, gender studies, and sexology. Recent findings suggest that radiation exposure, gravitational changes, and hypomagnetic fields may detrimentally impact our reproductive health. In addition, findings suggest that several gynecological risks related to spaceflights must be addressed (e.g., cancer, pregnancy, and contraception), along with many issues related to child-rearing, population diversity, reproductive and sexual rights, and intersectionality and social justice. More research is also needed on sexual responses and behaviors and the technologies that may facilitate safe sex, intimacy, and reproduction beyond Earth. Space poses significant risks to our sexual health. However, despite our space missions and objectives, this topic remains relatively understudied. There is an urgent need for a comprehensive scientific program on space sexology, one that holistically addresses the biopsychosocial realities of human eroticism. This is crucial for the well-being of our spacefaring civilization.


Introduction
We are going to space to stay. National agencies and private companies are racing to claim Earth's orbit, the Moon, Mars, and beyond. For instance, in 2022, the China National Space Administration completed its Tiangong space station, while the National Aeronautics and Space Administration (NASA) completed the first uncrewed launch of its This topic has frequently captured the attention of (non-) fiction media and the scientific community. This includes movies and TV series depicting intimate relationships in space (e.g., Star Trek, Battlestar Galactica, The Expanse, and Passengers), media articles questioning space agencies regarding the possibility and occurrence of sexual activities in space [12,13], as well as scholars and scientists advocating for increased attention and research on intimacy and sexuality beyond Earth [14••, 15, 16]. However, the current scientific study of extraterrestrial intimacy and sexualityor space sexology (also known as astrosexology)-remains limited and fragmented [14••, 15, 16].
Prior research has mainly focused on the impact of space conditions, such as radiation and microgravity on reproduction (e.g., gametes, fertility, and development [8•, 9, 17, 18, 19•, 20, 21•, 22, 23]). The private organization, SpaceBorn United, further seeks to facilitate the full reproductive cycle in space and adapt assisted reproductive technologies, such as in vitro fertilization technologies, to extraterrestrial conditions (i.e., a first test launch of their prototype is scheduled in 2023 [24,25]). That said, reproduction represents only a fraction of the challenges that space poses to human eroticism. In order to survive and thrive as a spacefaring civilization, we must fully consider the interconnected biopsychosocial factors associated with human intimacy and sexuality in space [14••].
But after three decades of calls for research in this area [14••, 15, 16], NASA only recently declared, "Should a future need for more in-depth study on reproductive health in space be identified, NASA would take the appropriate steps." (NASA representative, as quoted in [26]). Given the upcoming missions and objectives, this is a step in the right direction, but a more proactive effort to advance a comprehensive scientific agenda on space sexology is needed [14••, 27•]. To facilitate this effort, we must consolidate the existing knowledge on sexuality in space and answer the following research question: What is the current state of knowledge on sexual health in space? This article thus reviews the past 5 years of research on this topic and concludes with future research directions for space sexology.

Methods
The Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews (PRISMA-ScR) checklist and Arskey and O'Malley's (2005) five-stage methodological framework served as guidelines for this scoping review [28,29]. This scoping review was carried out in five stages: (1) identifying the research question, (2) identifying relevant articles, (3) article selection, (4) charting the data, and (5) collating, summarizing, and reporting the results.

Search Strategy
A literature search was conducted in the following databases: PubMed, Web of Science, Scopus, and PsycINFO. Searches were performed in November 2022 and updated in January 2023 with the assistance of a subject librarian. Additional studies were identified in the selected articles' reference lists. The database search included text word phrases, such as "spaceflight," "astronaut," "sexuality," and "reproduction." Truncation symbols (e.g., "*") were applied to detect variations in spelling and phrasing across sources. Synonymous terms were combined with the Boolean "OR," and the main concepts of interest were combined with Boolean "AND" (see supplementary materials for the full search strategy).

Inclusion and Exclusion Criteria
Articles were included in the review if they directly examined aspects of sexual health in spaceflights and under (simulated) space conditions. The selected articles had to be in English and published between 2018 and 2022. Abstracts, conference proceedings, and dissertations were excluded. The two authors independently screened titles and abstracts to assess articles for inclusion and exclusion. Any discrepancies during the screening were resolved through consensus.

Article Selection
A total of 249 articles were retrieved, and after removing duplicates, 130 unique records remained. Through screening of the titles and abstracts of non-duplicated records, 42 articles were found to be eligible for full-text review. Of these, 30 articles met the full inclusion criteria. Furthermore, an additional 20 articles were identified and included after examining the reference lists of the selected articles (see Fig. 1 for the PRISMA-ScR flow diagram).

Extraction and Categorization Strategy
Through an analysis of recurring topics in the literature and an iterative process of combining subtopics, the authors identified 11 interconnected content categories from the selected articles. These categories encompass research on radiation, gravity, hypomagnetic fields, gynecology and reproductive health, population diversity, children, evolution, reproductive and sexual rights, intersectionality and social justice issues, sexual responses and behaviors, and technologies that could facilitate intimacy in space.
The first two categories, radiation and gravity, represent the most extensively studied areas in relation to sexual health in space. Additionally, the authors found that research on the effects of hypomagnetic field is closely associated with these space hazards. The subsequent most researched topics include gynecology and reproductive health, as well as reproductive and sexual rights. Moreover, although topics such as intersectionality and social justice, population diversity, children, and evolution have received comparatively less exploration, they are still addressed or mentioned in some publications.
References to sexual responses and behaviors in space were infrequent and primarily centered on discussions of their occurrence in the past or their feasibility. Finally, the authors have identified research on technologies that could facilitate sexual activities, reproduction, and intimate relationships in space as a related area of study.
Of the 20 empirical articles, 17 employed non-human animal samples (e.g., cells, tissues, or data), while 3 employed human samples. Non-human animal samples included pigs (1), Grevenius annulatus (1), rats (1), fruit flies (4), and mice (11; i.e., one study used both fruit flies and mice). The three other empirical articles focusing on humans investigated the effects of microgravity on frozen sperm [30], whether female astronauts were at an elevated risk of venous thromboembolism due to contraceptive use through a review of longitudinal health data on female astronauts [31], and whether altered gravity affects the drug susceptibility of ovarian cancer cells [32].
Of the 13 review articles, 2 focused on humans, 2 on nonhuman animals, and 9 on both. These reviews incorporated samples from various non-human animal species, including  insects (e.g., fruit flies), rodent (e.g., rats and mice), amphibians/reptiles (frog, newts, and geckos), Echinoidea (e.g., sea urchins), fishes (e.g., zebrafish and killifish), crustacean (e.g., Echinogammarus marinus and Gammarus pulex), birds (e.g., quails), and large herbivores (e.g., rams). The review articles focused on humans generally included nonhuman animal data. They examined the gynecological and reproductive risks associated with spaceflights in female astronauts [21•, 22, 33], the effects of spaceflight on male reproduction [17], ectogenesis processes to colonize exoplanets [34], and how space may shape human evolution [35]. These reviews also examined the effects of microgravity on embryonic cells and development [18], spaceflights on humans and animal reproduction [8•], spaceflight-induced oxidative stress on female reproduction [9], high-LET particles on the reproductive processes and development [23], and hypomagnetic fields on biological systems [36]. Similar to review articles, theoretical publications often incorporate information from non-human animal sources but largely focus on human realities. They address the gynecologic considerations of female astronauts [37 ••, 38], review the research on mammalian reproduction and (embryonic) development under space conditions [39,40], and explore the challenges associated with human sexuality and reproduction during long-duration spaceflights (e.g., logistical, social, biological, and ethical [11•, 27•]). Beyond that, these publications examine the evolutionary implications of human space exploration [7], space-related rights and legislative frameworks [41][42][43][44], as well as the history of American female astronauts' participation in space endeavors [45]. They also discuss the ethical issues related to spacelife [46,47], with Szocik [48•] introducing space bioethics as a new branch of space philosophy.
Overall, 12 publications focused on male-related issues (e.g., sperm, testes, spermatogenesis, testicular function, male reproduction, and male reproductive organs), 13 on female-related issues (e.g., oocytes, ovaries, ovarian cancers, contraception, estrous cycle, gynecological considerations, female reproduction, female astronauts' health), and 25 on issues linked to all sexes (e.g., embryonic development, reproductive rights, vertebrate reproduction, reproductive and sexual rights, risks-benefits of sexuality in space, and the effects of space conditions on reproductive health). Still, the prevailing consensus is that additional research is required on human intimacy and sexuality in space. To address this gap, Dubé et al. [14••] proposed a biopsychosocial framework to guide transdisciplinary research on space sexology.
To further aid this objective, this review presents the current state of knowledge on sexual health in space through 11 categories that reflect the main topics covered in the past 5 years. It should be noted that the order of presentation of these categories is designed to avoid redundancies, strategically provide key information to the reader, and offer a narratively compelling flow. For instance, environmental hazards are presented before gynecological risks, and issues related to population diversity, pregnancy, and children are addressed before reproductive and sexual rights. This sequencing allows the reader to better comprehend the necessity for each research area (e.g., space gynecology, human rights beyond Earth, and the use of technology as a potential solution to space challenges).

Radiation
Radiation exposure can lead to DNA damage, which may have severe consequences on human health, including our sexual and reproductive health [8•]. Research suggests that the effects of radiation on females, males, embryos, and fetuses differ and depend on the dose and developmental stage [23]. Ovaries, oocytes, and spermatogenic cells are highly sensitive to radiation, and this sensitivity seems to increase with age [8 •, 23].
In females, radiation exposure may heighten the risks of pregnancy-related complications, such as miscarriage, preterm birth, and gestational diabetes [9]. It may also cause sterility, ovarian tumors, premature ovarian failure, damages to primordial follicles, suppression of ovulation, and depletion of ovarian reserves, leading to a decrease in the time interval to menopause and an increase in the risk of early mortality [8•, 38, 49]. Still, the impact of space radiation is not well understood due to ethical considerations and the limited exposure of female astronauts to such conditions [14••, 33]. In males, research suggests that radiation exposure may reduce sperm count and cause sterility [8•, 17, 23]. In contrast, Wakayama et al. (2021) also found that radiation did not affect mouse sperm DNA preserved on the International Space Station, and the samples produced genetically normal offspring [50].
Regarding embryos and fetuses, research suggests that radiation exposure may cause oxidative stress, epilepsy, microcephaly, growth delays, congenital malformations, cognitive impairments, neurobehavioral effects, embryonic death or developmental defects, and elevated risks of neonatal mortality [19•, 23, 40, 51]. Moreover, although preimplantation mouse embryos can develop in space, there is a reduced rate of blastocyst formation and quality. Overall, more research is needed to mitigate the risks of radiation exposure [40]. Solutions may include radiation shielding, hormone replacement therapy, cortical tissue freezing, as well as oocyte and sperm cryopreservation [38,52].

Gravity
Gravitational changes can affect biological processes. For instance, Mishra and Luderer (2019) proposed that hypergravity during mating and neonatal periods may decrease pregnancy rates and neonatal survival, while Ogneva and colleagues (2022) have shown that overloads and readaptation to Earth's gravity may affect sperm motility [8•, 53]. Microgravity, on the other hand, may affect cell morphology, increase apoptotic cell percentage, cause cell cycle arrest, and alter cell proliferation and migration [32]. In females, microgravity may increase the risks of complications, such as miscarriage, preterm birth, neonatal mortality, and gestational diabetes, perhaps through the effects of oxidative stress [9,40]. It may also inhibit the growth of porcine granulosa cells and cause shape changes in them [54], as well as affect cellular mechanisms involved in cisplatin resistance, resulting in higher sensitivity of ovarian cancer cells to chemotherapy [32]. Additionally, microgravity may increase cellular respiration in fruit fly ovaries after a full cycle of oogenesis without changes in oocyte size or protein content in the respiratory chain [55]. One study further showed that the estrous cycle is present during spaceflight, and female mice may still be fertile [56]. These mice exhibited lower progesterone in space compared to their baseline, while no differences in ovarian tissue steroid levels and genes involved in steroid production were found [56].
In males, microgravity may decrease the number of mature spermatozoa in mice [57]. Usik and Ogneva (2019) later reported changes in the gene expression of cytoskeletal proteins in mouse sperm after a 30-day microgravity simulation [58]. Specifically, alterations in the expression of certain actin isoforms were observed after a 12-h recovery period, suggesting that the post-microgravity recovery period may be a time of increased mechanical stress. Yet, there is evidence that essential phospholipids can mitigate some of these effects by strengthening the stiffness of the cortical cytoskeleton [58]. That said, microgravity may affect gene expression and methylation in testes tissues [59]; disrupt spermatogenesis and testosterone synthesis [8 •]; cause a decrease in body weight, semen parameters, and testicular and epididymal weights [60]; increase DNA fragmentation; and reduce testosterone levels, sperm motility, and total sperm count [17,61].
Despite these findings, Matsumura et al. (2019) found that short-term stays in outer space did not cause overt defects or changes in gene expression in mouse reproductive organs exposed to microgravity [62]. The mouse sperm fertilized oocytes in vitro and resulted in comparable levels of pups, with no significant differences in growth rates or fecundity [62]. Similarly, examining the effect of gravity on the testes and duct deferens tissues of mice exposed to 21-24 days of space flight conditions, Ogneva et al. (2019) found some changes in gene expression, but no changes in DNA methylation and cytoskeleton and sperm proteins [63]. Boada et al. (2020) further found that frozen sperm did not show changes after exposure to microgravity in terms of progressive motility, vitality, morphology, DNA fragmentation, and apoptotic sperm [30]. Furthermore, microgravity seems to increase the speed of fly spermatozoa and decrease that of mouse spermatozoa [61,64]-suggesting some species-specific reaction to such conditions. There is also some evidence suggesting that hypergravity may have a greater detrimental impact on sperm motility than microgravity [65].
Finally, microgravity may be detrimental to embryos and fetuses. For example, while preimplantation embryos may be able to develop in space, they show reduced rate of blastocyst formation and quality, as well as severe DNA damage and hypomethylated genome [20,51]. Through the effects of oxidative stress, microgravity may also lead to embryonic developmental defects [9,40]. Nevertheless, more research is needed to differentiate the effects of radiation exposure, microgravity, and oxidative stress [8•, 9, 18, 39, 51]. Further research is necessary to examine signaling pathways, transcription factors, stress response, epigenetics, and the long-term effects on offspring, as well as develop solutions [18,39,40,51]. Notably, geckos and other reptiles may represent effective models to study reproduction and development in weightlessness [19 •].

Hypomagnetic Field
Hypomagnetic field may impair animal systems (e.g., the central nervous system) and act as a stressor [36]. In terms of reproduction, Ogneva et al. (2020) found that hypomagnetic conditions may decrease fly sperm motility and cellular respiration, but after 1 h, cellular respiration actually increased [64]. Additional research is required to understand the impact of hypomagnetic fields on reproduction, including intensity effects, countermeasures, and interactions with other factors, such as radiation and microgravity [36].

Gynecology and Reproductive Health
Gynecological and reproductive health considerations during (long-term) spaceflights include anemia, fertility, contraception, ovarian cysts, (ectopic) pregnancy, childbirth, abnormal uterine bleeding, bone mineral density loss, developmental anomalies of the embryo or fetus, and venous thromboembolism [21•, 27•, 44]. Female astronauts also tend to have their children later in life, which may increase rates of infertility or risks of miscarriage [37••]. Yet, current data from female astronauts suggest that most gynecological and reproductive problems can be addressed [37••]. To do so, preventive measures and physiological countermeasures against radiation and weightlessness are necessary [37••]. Personalized medical care and mission-specific crew training in telemedicine may also be necessary, especially for long-duration missions [37••].
Regarding venous thromboembolism, Jain et al. (2020) found no evidence of elevated risk in female astronauts during spaceflight, regardless of contraceptive use [31]. Still, the desirability of contraception or menstrual suppression and the risk-benefits of hormonal modalities must be considered [22]. The impact on onboard mass, volume, and engineering considerations must also be taken into account in the decision-making process related to menstrual management, pregnancy prevention, and gynecological-related pathologies in space, with the final decision always left to the astronaut [22].
Overall, the effects of space on gynecological or reproductive health remain largely unknown [21•]. Data on conception, gestation, and development in space are limited and conflicting [27•]. More research is needed, including investigations into ways to avoid risks related to maternal and fetal health, crew morale, and mission success [22, 27 •].

Population Diversity
The composition and genetic diversity of the population living on remote worlds or aboard spacecraft traveling long distances is also a concern [11•, 14••]. Some scholars have estimated the minimum viable population to be 5000 people, but this number can decrease if we include genetic and enhancement technologies or increase if we consider possible sociocultural or cataclysmic issues that may occur in space [11•]. Relatedly, some scholars have argued that we may need to constantly bring in new settlers and/or gametes and fertilized eggs, perform genetic and disease screenings, closely monitor the health of fetuses, and consider the implementation of legislative termination frameworks to ensure sustainable genetic health for space populations [43]. In this way, genetic diversity may be maintained through autonomous pairings and genetic/technological health interventions [42]. Population growth issues may also be prevented via education, contraception, and consensual limits on the number of children [56]. Importantly, we must also foster sufficiently diverse populations to accommodate various gender identities, sexual orientations/preferences, intimate relationship structures, and the reproductive autonomy of space inhabitants [11•, 14••, 46].

Children
Raising children in space without their consent may also be ethically questionable. Schwartz (2018) argues that, if we do so, we should consider the diverse forms of child-rearing that exist in our societies and ensure opportunities for personal growth, education, vocation, gender identity, sexual orientation, and reproductive autonomy [46]. We should also uphold reproductive autonomy rights and, perhaps, the right to return to Earth [41,46]. As Cowley (2019) points out, however, people living or born in space (e.g., on Mars) may face physiological and psychological changes that could make this return difficult [41]. We should therefore plan to provide spaceborne children with safe and fulfilling living environments, as well as technological means that facilitate autonomy and freedom of movement.

Evolution
Humans have evolved under Earth conditions, such as a gravity of 1 g, a geomagnetic field, and a certain level of background radiation [35]. However, these conditions change in space. Researchers thus anticipate that, as humans reproduce in space, future generations may progressively exhibit or require physiological and psychological changes, and undergo a process of speciation [7,41]. For instance, they argue that microgravity and radiation may affect human health and evolution, so we may need to adapt our reproduction to these conditions [35]. It has also been proposed that evolutionary perspectives and sexually reproducing nonhuman animal models could help to study, understand, and cope with such phenomena [7,35].

Reproductive and Sexual Rights
Just as on Earth, human rights related to reproductive and sexual health must be protected in space. This includes the right to life, health, privacy, education, and freedom from discrimination [44]. Women's rights, as well as that of vulnerable and marginalized groups, may also require special care [44]. Legal aspects related to intimacy may be particularly challenging in space given the living conditions, sociocultural realities, and power dynamics that may arise [44].
For example, designing reproductive and sexual rights and policies may be challenging due to political (e.g., liberal or conservative) and sociocultural differences, including norms and values [11•, 43, 44]. Still, ensuring that space inhabitants maintain their reproductive autonomy and bodily integrity regarding intimacy and procreation, including rights to partner choice, sexual preference protections, and the choice to have children (or not), remains crucial [11•, 41, 42].
The implementation of policies may be needed to ensure the well-being and sustainability of space habitats [27•]. This may include abortion and consensual one-child policies [11•, 42]. Issues related to sterilization, gene editing, embryo selection, prebirth screenings, crew selection policies, and equal access to space will also need to be discussed and carefully examined [48•]. A feminist bioethics approach to space philosophy and ethics may arguably help to tackle these challenges (e.g., avoid male-centrism and favor intersectional and women-centered perspectives [48•]).

Intersectionality and Social Justice
Certain groups, such as women/females, Black, Indigenous, and People of Color (BIPOC) community members, gender/ sexual minorities, and individuals living with disabilities, may disproportionately face risks associated with space exploration [14••, 45, 48•]. For instance, ethical considerations related to space reproduction have a more significant impact on individuals with female bodies as there are risks of being subjected to pregnancy coercion and pregnancyrelated health problems [47]. Moreover, toxic patriarchal sociocultural norms and the relative physical strength of men may pose greater threats to women and non-cisgender men (e.g., sexual assault or harassment [14••]). Gender and sexual minorities may struggle to find compatible partners and may be at greater risk of discrimination and mental health issues [14••]. Prior research further suggests that certain risks disproportionately affect the cardiovascular, musculoskeletal, immune, neurosensory, and reproductive systems of female astronauts [8•, 14••]. Addressing intersectionality, social justice, and biopsychosocial challenges related to diversity, equity, and inclusion in space exploration is critical [14••].

Sexual Responses and Behaviors
There is evidence that sexual responses (e.g., erections) are not suppressed in space [66]. To date, however, no astronaut has officially had sex in space, either solitary or partnered. Some scholars have proposed that sex in zero gravity may be challenging due to weightlessness, which may influence blood flow, arousal, and lubrication. Equipment and artificial gravity systems hold the potential to remedy some of these challenges [66]. But overall, little is known about sexual functioning in space. Considering future long-term missions, permanent bases, and the democratization of space tourism, more research is warranted [14••]. Beyond its health and relational benefits, sexual activities could help live happily in space and normalize spacelife [14••].

Technology
Lastly, living in space requires technology. This applies to human intimacy and sexuality, too. For instance, adapted healthcare, artificial genetic engineering, and assisted reproductive technologies may be needed to safely bring new life into the world in space [11•]. Garments, like Vanna Bonta's 2suit, may also help keep partners together for intimate or sexual interactions [66], and artificial uteri may be used to help with premature pregnancies, people who cannot have children, and to facilitate space settlements [34]. Genetic modifications or enhancements may further be used to ensure human survival in space, from gametes to adulthood [47].
Additionally, technologies, such as sex toys and artificial erotic agents, may be used to fulfill the intimate needs of astronauts [14 ••]. These technologies could provide safe and hygienic access to sex and intimate relationships for astronauts both in and outside of their crew [14••]. They could also help connect intimate partners at a distance, mitigate some of the hardships associated with involuntary abstinence, and monitor the health and well-being of people living in space [14••]. To ensure space-compatibility, such products should be light, discrete, easily cleaned, and produce little to no waste [14••].

Discussion
If we aim to perform long-term spaceflights and settle new worlds, we must address the intimate and sexual realities of human spacelife [14 ••]. To help in this endeavor, this article reviewed the past 5 years of research on sexual health in space. This review yielded fifty publications, most of which are empirical papers. There were also some reviews, theoretical papers, book chapters, and other publications, such as chapter subsections, a commentary, and an expert opinion. Most of the research was rooted in biology, but other publications came from fields such as philosophy, ethics, and law, gynecology and obstetrics, aerospace medicine, gender studies, and sexology. The majority of empirical studies and review articles are based on non-human animal models, with only a few studies involving human models. Non-human animal models include various species of amphibians, reptiles, fishes, birds, Echinoidea, crustaceans, insects, and rodents.
To date, the research on sexual health in space mainly focuses on the effects of radiation exposure and microgravity on male and female reproduction. Other topics discussed include the gynecological and reproductive risks of spaceflight, human evolution beyond Earth, and the technologies that may be necessary to enable sex and reproduction in space. It also includes topics such as the feasibility of sexual activities occurring in space, as well as the ethical and social implications of space eroticism, including reproductive and sexual rights, population diversity, child-rearing, and issues related to intersectionality and social justice.

Current State of Knowledge
Current research suggests that radiation exposure can cause DNA damage and detrimentally impact both female and male gametes and reproductive organs [8•, 23]. In females, radiation exposure may damage follicles and cause sterility, ovarian failure, and tumors, which may decrease the time interval to menopause and increase the risks of early mortality [8•, 38, 49]. It may also raise pregnancy risks, such as miscarriage and preterm birth [9]. In males, radiation exposure may reduce sperm count and cause sterility, but there is evidence that male gametes may be safely stored in space for extended periods [8•, 17, 23, 50]. When it comes to embryos and fetuses, research suggests that radiation exposure can lead to growth delays, cognitive impairments, congenital malformations, and heightened risks of neonatal mortality [19•, 23, 40, 51]. The severity of radiation effects depends on the dosage and developmental stage [23] and may interact with the effects of hypomagnetic field and gravitational changes [36].
Indeed, changes in gravity can also impact reproductive processes during spaceflights. For instance, hypergravity during mating and neonatal periods may decrease pregnancy rates and neonatal survival [8•], while readaptation to Earth's gravity may affect sperm motility [53]. Conversely, microgravity may also affect cell morphology, increase the percentage of apoptotic cells, cause cell cycle arrest, and alter cell proliferation, migration, and growth [32]. In females, microgravity may increase risks of miscarriage, preterm birth, neonatal mortality, and gestational diabetes [9,40]. In males, it may decrease spermatogenesis, sperm count, and motility, reducing testicular and epididymal weights, as well as disrupting testosterone synthesis in males [8 •, 17, 57, 59-61]. When it comes to embryos and fetuses, microgravity may further reduce hypomethylated genome and blastocyst formation and quality, as well as increase risks of embryonic developmental defects [9,20,40,51]. Encouragingly, despite lower progesterone levels, female mice still exhibited an estrous cycle and fertility in space [56]. Moreover, short-term exposure to spatial microgravity does not seem to cause significant defects in gene expression in mouse reproductive organs [62], and frozen sperm does not show changes after exposure to microgravity [30]. Noteworthy, the effects of radiation and gravity may also interact with the impacts of hypomagnetic field in space [36].
Several other considerations have also been discussed. For one, there are many gynecological and reproductive health concerns related to spaceflights, including anemia, cancer, fertility, contraception, menstrual cycles, pregnancy, and miscarriage, as well as female astronauts having children later in life, which increases risks of pregnancy-related complications [21•, 27•, 37••, 44]. Some researchers assert that the majority of these concerns can be addressed through a combination of personalized medical care, countermeasures (e.g., against radiation and weightlessness), and missionspecific crew training [37••]. Notably, female astronauts do not seem to be at increased risk of contraceptive-related venous thromboembolism during spaceflight [31]. Still, the decision-making process related to menstrual management, pregnancy prevention, and gynecological-related pathologies in space should consider the risk-benefits of hormonal modalities, and the final decision should always be left to the astronauts themselves [22, 37••].
The composition and genetic diversity of the population in remote worlds or spacecrafts is also a concern [11•, 14••]. To avoid genetic-based issues and problems related to people having difficulty finding intimate partners, as well as to overcome potential health crises or cataclysmic events, a minimum viable population is necessary (e.g., 5000 individuals [11•]). Population diversity can be aided by genetic and disease screenings, termination frameworks, autonomous pairings, education, and contraception, as well as bringing new settlers and genetic material into space populations [42,43]. Population diversity can be aided by ensuring that a sufficient number of people are living in settlements or spacecrafts to accommodate different gender identities, sexual orientations/preferences, and reproductive autonomy of space inhabitants [11 •, 14••, 46].
Relatedly, we must further ensure that children born in space are safe and have decent lives that allow them personal growth, access to education and healthcare, and the expression of their sexual-self (e.g., identity, orientation, and preferences) [46]. These spaceborn children may further need a guaranteed right to return to Earth, which may be difficult to uphold if these individuals undergo psychophysiological changes or are too far from our planet to return [41]. As some scholars have suggested, spacelife may induce and/or require physiological and psychological changes that may eventually lead to speciation in future human generations and make it challenging for these people to (re)adapt to Earth conditions [7,35,41].
In parallel, human rights related to reproductive and sexual health will need to be protected in space, including those of women and vulnerable/marginalized groups [44]. Policies may need to be implemented to ensure the sustainability of space habitats (e.g., abortion and one-child policies) and manage issues related to sterilization, gene editing, and embryo and crew selection [11•, 42-44, 48•]. Legal and ethical aspects related to intimacy, informed consent, and population sustainability may be particularly challenging due to diverse sociocultural and power dynamics that may arise in space habitats [11•, 43, 44]. In that regard, a feminist bioethics approach may help to address these challenges [48•].
Feminist, intersectional, and social justice approaches remind us that certain sociodemographic groups, such as women, BIPOC community members, gender/sexual minorities, and individuals living with disabilities, may be disproportionately affected by some of the risks associated with space exploration [14••, 48•]. This may include toxic patriarchal sociocultural norms and the relative physical strength of men, which may pose greater threats to women and non-cisgender men [14••]. It may also involve realities that gender and sexual minorities will have more difficulty finding compatible partners and be at greater risk of discrimination and mental health issues [14••]. This brings to the forefront the importance of considering diversity, equity, and inclusion issues as we venture into space [14••].
Lastly, while technically possible, there are no official reports of solitary or partnered sex beyond Earth [66]. Similar to other aspects of spacelife, technology may help address challenges related to sex, intimacy, and reproduction. Such technology may include artificial uteri, genetic modifications, and adapted health monitoring and care [11•, 34, 47, 66]. Sexual technologies, such as sex toys and artificial erotic agents compatible with space habitats, could also help to fulfill astronauts' intimate needs [14••]. Abstinence is neither a viable nor ethical option [14••].

Limitations and Strengths
This review is not without limits. For one, it is limited to the past 5 years of research that the search terms and engines employed. It did not include abstracts, conference proceedings, and dissertations. It also does not comprehensively cover research on gender/sex differences in spaceflight and embryonic development indirectly connected to space conditions-topics that may warrant distinct reviews. More to the point, the distinctions and intersections between sex and gender are unclear, with most of the literature presented focusing on biological (binary) sex (i.e., female and male). Still, this review highlights the current state of knowledge on sexual health in space, which will help identify gaps and research opportunities and develop a comprehensive scientific agenda on space sexology.

Conclusion
Space can detrimentally impact our reproductive and sexual health. As we venture further into space, it thus becomes imperative that more research be conducted on human intimacy and sexuality beyond Earth. Future research directions include but are not limited to disentangling the respective effects of radiation exposure, gravitational changes, and hypomagnetic fields on reproductive functions and structures [8•, 9, 18, 39, 51], devising solutions to address the gynecological risks of (long-term) spaceflight [36], and establishing mission-specific minimal viable populations [11•, 14••, 46]. Future research also includes putting in place evidence-based mechanisms that consider intersectional and social justice issues and protect the sexual and reproductive rights of all space inhabitants (e.g., policies, protocols, frameworks, and countermeasures), as well as ensuring safe space reproduction, from conception and pregnancy to birth and comprehensive child-rearing [11•, 14••, 42-44]. Finally, comprehensive biopsychosocial research is urgently needed on human samples and subjects, including on gametes, reproductive tissues, sexual functioning, and intimate relationships, in analog, simulation, and whenever possible space environments [14••]. A broad scientific agenda on space sexology is needed to better understand the sexological realities of human spacelife [14••, 15, 16]. The future of our spacefaring civilization depends on it.