Why does high humidity make it feel hotter?
Quick Answer: High humidity makes it feel hotter because moisture in the air slows down your body's sweat evaporation, which is how you cool off. When sweat can't evaporate easily, your body stays warm and you feel hotter than the actual temperature.
When the air is humid, it’s already packed with water vapor. This reduces the rate at which sweat evaporates from your skin. Since evaporation is a cooling process, less evaporation means less cooling.
Your body keeps producing sweat to cool down, but the sticky air leaves it sitting on your skin instead of drying quickly. That trapped moisture makes you feel hotter and more uncomfortable, even if the thermometer’s not higher.