Just like the humid air in summer seems to add a few degrees to the temperature, the same goes for indoor air. This enables you to set your furnace to a lower temperature while still achieving maximum warmth and comfort. Dry air can cause sore throats, dry skin, itchy eyes, and bloody noses—it can also be a contributing factor in catching a cold or flu. A healthy level of humidity is between 35 and 50 percent. Too much humidity can increase airborne mold, bacteria, and fungi that, when ingested, can lead to other health concerns like infections, asthma, allergies, and other respiratory illnesses.