Some patients who recover from COVID-19 have prolonged symptoms such as dyspnea, fatigue, cough, and dysosmia for longer than 120 days after symptom onset. In addition, some patients who recovered from COVID-19 reported hair loss a few months after the onset of the disease. Alopecia is a late-onset symptom of COVID-19. The cause of alopecia is unknown, however, androgenic alopecia and telogen effluvium are possible causes.

Space travel has advanced significantly over the last six decades with astronauts spending up to 6 months at the International Space Station. Nonetheless, the living environment while in outer space is extremely challenging to astronauts. In particular, exposure to space radiation represents a serious potential long-term threat to the health of astronauts because the amount of radiation exposure accumulates during their time in space. Therefore, health risks associated with exposure to space radiation are an important topic in space travel, and characterizing space radiation in detail is essential for improving the safety of space missions. In the first part of this review, we provide an overview of the space radiation environment and briefly present current and future endeavors that monitor different space radiation environments. We then present research evaluating adverse biological effects caused by exposure to various space radiation environments and how these can be reduced. We especially consider the deleterious effects on cellular DNA and how cells activate DNA repair mechanisms. The latest technologies being developed, e.g., a fluorescent ubiquitination-based cell cycle indicator, to measure real-time cell cycle progression and DNA damage caused by exposure to ultraviolet radiation are presented. Progress in examining the combined effects of microgravity and radiation to animals and plants are summarized, and our current understanding of the relationship between psychological stress and radiation is presented. Finally, we provide details about protective agents and the study of organisms that are highly resistant to radiation and how their biological mechanisms may aid developing novel technologies that alleviate biological damage caused by radiation. Future research that furthers our understanding of the effects of space radiation on human health will facilitate risk-mitigating strategies to enable long-term space and planetary exploration.

The study of radiation effect in Caenorhabditis (C.) elegans has been carried out over three decades and now allow for understanding at the molecular, cellular and individual levels. This review describes the current knowledge of the biological effects of ionizing irradiation with a scope of the germ line, aging and behavior. In germ cells, ionizing radiation induces apoptosis, cell cycle arrest and DNA repair. Lots of molecules involved in these responses and functions have been identified in C. elegans, which are highly conserved throughout eukaryotes. Radiosensitivity and the effect of heavy-ion microbeam irradiation on germ cells with relationship between initiation of meiotic recombination and DNA lesions are discussed. In addition to DNA damage, ionizing radiation produces free radicals, and the free radical theory is the most popular aging theory. A first signal transduction pathway of aging has been discovered in C. elegans, and radiation-induced metabolic oxidative stress is recently noted for an inducible factor of hormetic response and genetic instability. The hormetic response in C. elegans exposed to oxidative stress is discussed with genetic pathways of aging. Moreover, C. elegans is well known as a model organism for behavior. The recent work reported the radiation effects via specific neurons on learning behavior, and radiation and hydrogen peroxide affect the locomotory rate similarly. These findings are discussed in relation to the evidence obtained with other organisms. Altogether, C. elegans may be a good "in vivo" model system in the field of radiation biology.

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Research concerning cellular responses to low dose irradiation, radiation-induced bystander effects, and the biological track structure of charged particles has recently received particular attention in the field of radiation biology. Target irradiation employing a microbeam represents a useful means of advancing this research by obviating some of the disadvantages associated with the conventional irradiation strategies. The heavy-ion microbeam system at JAEA-Takasaki, which was planned in 1987 and started in the early 1990's, can provide target irradiation of heavy charged particles to biological material at atmospheric pressure using a minimum beam size 5 mum in diameter. A variety of biological material has been irradiated using this microbeam system including cultured mammalian and higher plant cells, isolated fibers of mouse skeletal muscle, silkworm (Bombyx mori) embryos and larvae, Arabidopsis thaliana roots, and the nematode Caenorhabditis elegans. The system can be applied to the investigation of mechanisms within biological organisms not only in the context of radiation biology, but also in the fields of general biology such as physiology, developmental biology and neurobiology, and should help to establish and contribute to the field of "microbeam biology".