When the nest is harvested, the poor swift must rebuild and as time is limited it uses other fibers as well as saliva. The second nest, thus, is less nutritious. These nests are called mao yan (rough nests).

Most nests are translucent white or yellows (equally nutritious, color depending on bird's diet), but some are dark red and are called xue yan (bloody nest). The red comes from marine elements and iron in seaweed eaten by the birds. They are especially nutritious, quite rare and, of course, much more expensive.

Since harvesting nests on cliffs is life-threatening to the collectors and can damage the environment, tower-like structures are built for the birds to make their nests. They can fly in and out and harvesting is easy. They provide good spots for nest building and the birds lose less energy and nutrition flying about to find a nesting spot.

After they are harvested, the nests are cleaned and processed. They will be made into yan zhan (complete nest), yan tiao (nest stripes), yan bing (nest cake), yan si (nest thread), and yan sui (nest chips). Yan zhan made of the whole nest are most valuable.

Bird's nest is a neutral-energy tonic that reinforces energy, nourishes the lungs, benefits the spleen and improves the complexion. It travels through lung, stomach and kidney meridians to take effect.

It is used to treat various coughs, chronic bronchitis, vomiting, stomachache and malnutrition. It helps relieve night sweats and frequent urination due to energy deficiency.

"Bencao Gangmu" ("Compendium of Materia Medica") says bird's nest nourishes yin energy in the lungs, resolves phlegm and relieves coughing.

TCM holds that "the lungs govern skin and hair," and so bird's nest tonic can improve skin quality and reduce signs of aging.

Modern research has found the birds' saliva contains antioxidants and elements that promote cell regeneration. Rich protein and micro-elements can boost immunity.

Bird's nest is recommended for everyone. In addition to benefits already noted, it is said to be a male tonic. It can help pregnant women and nourish the fetus and help the elderly by increasing energy and treating respiratory and digestion problems.

As with all herbal therapy, it must be eaten regularly and it takes three to five months to have an effect. For complexion benefits, the best time to eat bird's nest is before you go to sleep; the "golden" sleep period is from 11pm-2am when cell division takes place around eight times faster than at other hours.