The immune system is the body's defense against infectious organisms and other invaders. Through a series of steps called the immune response, the immune system attacks organisms and substances that invade body systems and cause disease.
When the humidity is high it feels oppressive outside because sweat doesn't evaporate and provide cooling. When the humidity is low you feel cooler, but your skin dries out and you get dehydrated more easily because more moisture is being evaporated from your body. The same thing applies to crops in high and low humidity. A high water vapor content is necessary to produce clouds and precipitation.
We all recognize that summer is a time for warmer temperatures. But in addition to the effects of heat, personal comfort and health are strongly affected by the humidity -- the moisture content of the air. The combination of heat and high humidity may cause discomfort, heat stroke or even death to humans and animals.