This UN Women report argues that extreme heat is an intensifying climate risk and an under-recognized driver of gender and age inequality, with implications for public health, labour, and social justice. As global temperatures rise beyond 1.5°C, heat stress is no longer episodic but a structural challenge that disproportionately affects women, children, older persons, and marginalized populations, particularly in low- and middle-income countries. This paper shows that heat impacts emerge from the interaction of biological differences and gendered social roles. Physiological factors shape thermoregulation, fertility, and pregnancy outcomes, with elevated risks for pregnant women, newborns, and older women during heatwaves. Gendered divisions of labour and care amplify exposure. Women are overrepresented in subsistence agriculture, informal employment, and unpaid care and domestic work, often performed during the hottest hours with limited access to cooling, healthcare, and labour protections. Men, by contrast, experience high rates of acute heat injury in physically demanding outdoor occupations, reflecting exposure patterns and risk-discouraging norms. The paper introduces the concept of a "hidden heat burden": as droughts intensify, women's manual irrigation expands at peak heat hours, lengthening working days and crowding out rest, care and education, a pattern largely absent from labour statistics. Heat-driven migration is also on the rise: as men leave for cooler highlands or urban jobs, women are left to manage farms and households under harsher conditions.