Characteristics and Applications of Chemosensors for Biometric and Microclimate Measurements in AI Astronaut Suits: A Systematic Review

Background: Astronauts operating in extravehicular activity (EVA) and intravehicular activity (IVA) suits are exposed to a closed, thermally demanding microenvironment in which sweat accumulation, hydration status, skin-barrier disturbance, optical-signal interference, and changes in oxygen-carrying capacity can affect health, comfort, and task performance. This review therefore evaluates five sensing modalities—humidity, pH, sebum, melanin, and hemoglobin—not as general cosmetic sensors, but according to their potential roles in AI-enabled astronaut-suit monitoring. Methods: A systematic literature review was conducted using multidisciplinary scholarly databases and publisher platforms. From 1036 initially identified records, 187 full texts were screened, 135 reports were assessed for eligibility, and 93 studies were included. Studies were organized into humidity (n = 22), pH (n = 20), sebum (n = 16), melanin (n = 20), and hemoglobin (n = 15) categories and comparatively evaluated for sensing principle, quantitative performance, calibration requirements, wearability, environmental robustness, and relevance to astronaut-suit integration. Results: Humidity and pH sensing are currently the most directly compatible with textile or skin-interfaced suit architectures because they can provide continuous information on the local microclimate and sweat/skin chemistry. Hemoglobin sensing is promising for trend monitoring of oxygen-carrying status but requires careful optical calibration for pigmentation, motion, perfusion, and pressure effects. Melanin sensing is primarily valuable as a calibration and radiation/optical-context variable rather than as an acute physiological alarm, whereas continuous sebum sensing remains comparatively immature for operational spacesuit use. Edge artificial intelligence (AI) can support multimodal sensor fusion, artifact rejection, personalized baselines, anomaly detection, and tiered alerts without implying stand-alone disease diagnosis. Conclusions: The five modalities have different levels of technological readiness for astronaut suits. Near-term research should prioritize humidity, pH, and optical hemoglobin trend monitoring, while treating melanin as a correction/context variable and sebum as an exploratory skin-barrier marker. Translation to EVA/IVA use requires standardized calibration, low-power edge processing, long-duration biocompatibility, resistance to sweat, pressure, motion and thermal cycling, and validation in suited analog environments before flight deployment.