Often, the water from air conditioners can drip out into the casing in the hot part of the unit. This hot, wet environment is especially fertile for microbe growth. The air conditioner picks up and spreads the microbes whenever it blows the air, which can spread a variety of diseases. In fact, air conditioning was the original source of Legionnaire’s disease. In addition to growing microbes, an air conditioner can make you more vulnerable to the microbes you inhale, further increasing your susceptibility to illness.