When you inhale a cigarette, your airways get covered in a sticky black tar, making it hard to breathe. The chemicals kill the tiny hair-like structures inside that help clear out mucus and dirt. And without them, harmful substances build up, causing infections and coughing.
Over time, the smoke scars your lung tissue, making them stiff and weak. And eventually, your lungs become too damaged to function, leaving you unable to breathe on your own.