The vocal folds vibrate in response to a stream of air flowing out of the body. The voice box and the breathing areas above it (the upper respiratory tract) also filter the air coming into the body. The quality of air coming in affects the health of the entire area.
Both your nose and your mouth — the entry passages for air — are lined with moist mucous membranes. Air passing through these passages picks up moisture and begins to match the inner body temperature. While the mouth is a large, simple opening, the nose is a curly “obstacle course,” allowing a more prolonged effect on environmental air.
The nasal membranes also contain thousands of microscopic hairs (cilia) whose job is to catch dust, allergens, and anything else that could hurt your lungs. By the time air gets to the voice box, it is warm, humid, and filtered.
If these entry passages are overly dry — because the nose is congested and one breathes only through the mouth, or perhaps because medication or whole-body dehydration have decreased fluid levels between cells — the larynx will also become dry.
Other airborne problems for the voice come in the form of irritating chemicals, extreme temperatures, or infectious bugs that the nose and mouth didn’t catch. The most common, controllable irritant is cigarette smoke, discussed in the section titled “Tobacco, Alcohol, and Marijuana.”