In this comprehensive review, we explore the intersection of reactive materials in fiber sensor technology and the critical role of humidity control in mechanochemical treatment processes. We examine recent advancements in embedded sensor technologies, focusing on their applications in various treatment processes across industries. We highlight the development of metal oxide nanomaterials as effective optoelectronic humidity sensors, discussing their fabrication, characterization, and operational principles. In this review, we also delve into the emerging field of wearable chemical sensors, emphasizing their potential in healthcare monitoring and environmental applications. Furthermore, we address the integration of embedded sensors in Industry 4.0 frameworks, illustrating their impact on factory automation, process optimization, and sustainable manufacturing. We underscore the importance of humidity control in mechanochemical treatments, linking it to the broader context of sensor technology applications. By unifying current research and identifying future trends, we provide valuable insights into the synergies between reactive materials, fiber sensor technology, and humidity control, offering a foundation for further innovations in treatment process enhancement and efficiency.