To understand how smoke damages the lungs directly you must understand how they work. The lungs are responsible for taking oxygen out of the air in exchange for excess carbon dioxide in the body. The lungs are divided into thousands of tiny sacs with very delicate surfaces. Just beneath the thin layer of surface cells are the blood vessels that must pick up oxygen and shed carbon dioxide. A breathe lasts a few seconds so the exchange must happen fast. That is why there are so many little sacs and why their surfaces must be so thin and fragile. Moving little molecules of oxygen and carbon dioxide would not happen if the barriers were large.
Now imagine all these tiny sacs being awash not in life sustaining oxygen but hot, chemical-enriched smoke. The chemicals in smoke enter the bloodstream along with oxygen and are spread throughout the body. Just as bad, over time the sacs of the lung darken and then burst. Like soap bubbles, once they start to burst, a chain reaction occurs and soon they disappear. That is what happens with smoking, and it is called COPD (Chronic Obstructive Pulmonary Disease). You can pour oxygen into the lungs and nothing will happen. It is a painful death: slow suffocation.
Smoke also erodes the fine hairs called cilia that line the upper airways. Like infinitely small blades of grass they sway in coordinated waves to remove any particles or mucous that might find their way into the lungs. Once they are gone, infections and accumulations of mucous and foreign material can gather in clumps in airways. It’s a mess.