To keep your lungs healthy, the layer of mucus that covers the windpipe and bronchial tubes must be moist enough to be pushed along easily, and the tiny pushy cilia must remain strong and busy. Infection, smoking, lack of fluids, and allergies can stun or cripple the cilia, and can alter the consistency of the mucus.
When this beautiful system is challenged, damaged, or clogged, the incoming irritants and microbes are either trapped against the wall of the respiratory tract like a dirty bandage that rarely gets changed, or the irritants find an unobstructed, direct path into the deep lungs and ultimately into the bloodstream. Without the cooperative efforts of the cilia and mucus blanket, your crippled respiratory system is finally unable to cleanse itself.
Be well. Breathe beautifully.
LINK: The Path From Throat To Lungs