Healthy lungs ensure that abundant oxygen is transported from the air into the bloodstream while as much carbon dioxide is released from the blood and expelled from the body. The lung capacity or vital capacity is a measurement of the lungs' ability to respire, and starts to decline around the age of 30.

When the lungs are weakened, a basic task like climbing a flight of stairs may leave you breathing more heavily. One may experience lack of physical strength, reluctance to talk, and a pale complexion. These are indications of Lung Qi deficiency in traditional Chinese medicine (TCM). Another common type of Lung weakness is Lung Yin deficiency, which is shown as occasional cough without spitting out mucus, scratchy throat, hot palms and soles, and night sweat etc. Smoking cigarettes is a common cause of Lung Yin deficiency.

Bai He Gu Jin Tang is a popular Chinese herbal medicine used to replenish the Lung Yin energy. As the lungs are characterized as "Metal" in TCM and Bai He or lily is the chief Chinese herb in the herbal formula, it becomes the name of "Lily Strengthen Metal".

Bai He (Lily bulb) is the chief Chinese herb in the formula that nourishes the lung Yin energy and moistens the lungs. Lily also has an effect on clearing lung heat.

Di Huang (Rehmannia root), used in both raw and prepared forms, is also a chief herb in the formula. The Chinese herb nourishes Yin and tonifies the kidneys. In addition, the raw Rehmannia root clears heat and generates fluids to relieve thirst. The combination of Rehmannia and Lily serves to enforce each other's function in replenishing lung (metal) and kidney (water).

Mai Men Dong (Ophiopogon tuber) may nourish the Lung Yin energy, moisten the Lungs, and clear Lung heat, thus enhancing the Lily's effectiveness.

Xuan Shen (Scrophularia root) nourishes Yin and reduces Fire and assists the action of Rehmannia.

Bei Mu (Fritillaria bulb) moistens the lungs and transforms phlegm.

Jie Geng (Platycodon root) ventilates the lung and clears phlegm.

Gan Cao (Licorice root) The Chinese herb moistens the lung and transforms phlegm. It is often combined with platycodon root.

Dang Gui (Angelica root) and Bai Shao (Peony root) nourishes the blood to benefit the Yin energy.