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.
To make matters worse, when humidity levels dip the ambient air feels cooler than more humid environments, and we turn up the heat to compensate. Low humidity causes static electricity, dry skin and hair, increased susceptibility to colds and respiratory illness, and can allow viruses and germs to thrive. Wood floors, furniture and millwork will split and crack, paint will chip, and electronics can be damaged because of low humidity levels.