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.
Humidity can make the warmth of the surrounding air feel as if it is warmer than the actual temperature would suggest, because the cooling effect of evaporation from the skin is reduced. This is because as environmental temperatures approach normal skin temperature, cooling of the body becomes more difficult.