Humidity control is very important to your health for a couple of reasons. Mold, which thrives in high humidity, is dormant or dies when the humidity is low. Dust mites also die when the humidity stays below 50%. But remember, the dust mites in your bed rely on you for their source of humidity, so always use mattress covers, pillow covers and box spring encasings.
On the other hand, below 30% relative humidity, people can be uncomfortable and can suffer from dry mucus membranes which can lead to nosebleeds and infections. Low humidity can aggravate the symptoms of asthma and high humidity at high temperatures can sometimes lead to heat exhaustion or heat stroke. Control humidity with proper ventilation and air conditioners, humidifiers or dehumidifiers.