Why do hot humid days pose such a risk of heat illness during vigorous physical activity?

Hot humid days increase the risk of heat illness during vigorous physical activity because high humidity levels impede the body's ability to cool itself through sweat evaporation. When sweat cannot evaporate efficiently, the body struggles to regulate its core temperature, leading to overheating. Additionally, the combination of elevated temperatures and humidity can cause dehydration, further exacerbating the risk of heat-related illnesses such as heat exhaustion or heat stroke. Consequently, it is crucial to take precautions, such as staying hydrated and avoiding intense exercise during peak heat and humidity.