Mental stress is a prevalent health issue that substantially impacts productivity, quality of life, and general well-being. Real-time stress detection and management have become possible because of the rapid advancements in machine learning and wearable sensor technology. This paper explores these emerging technologies and their application to mental stress detection, providing insights into the underlying factors influencing stress responses. We examine stress's physiological and psychological factors, highlighting critical biomarkers like heart rate variability (HRV) and electrodermal activity (EDA), which can be reliably captured through wearable sensors like ECG and PPG. Our analysis covers the essential detailing of the capabilities of various wearable sensors, data transfer and signal processing technologies, and data handling techniques that transform raw signals into meaningful stress indicators. Additionally, we delve into ML approaches for stress detection, comparing traditional algorithms with advanced models capable of recognizing complicated stress patterns from multimodal data. Furthermore, we address key challenges such as sensor quality, data diversity, and individual health variability that influence the robustness and accuracy of stress monitoring systems. This work underscores the potential of wearable sensor data and ML to present precise, proactive stress management solutions that could transform mental health monitoring and enhance intervention strategies.