Hello Smoking habits can be stop gradually by healthy habits like chewing lavang, smells lavender r tea tree aroma oil , eucalyptus oil.it give pleasant feeling and it helps to overcome smoking habit. And for rejuvenate lungs.follow natural cleansing treatments,yoga , healthy diet.thulsi kasayam its a divine medicine to cleans the lung.with proper sleep.

Hi, smoking causes damage to lungs, when he inhales smoke which contain various gases that causes damage to alveoli( smallest unit in lung for gaseous exchange). Usually damage is irreversible, only way to prevent from furthur damage is by stoppage of smoking. If he stops now we can save him from diseases like copd ,asthma, lung cancers, etc. He can go for nearby rehab centres. Do yoga, pranayama,regular excercises. Go for chest xray ,Consult general physician for furthur care.