What is phytoncide?

Phytoncide is the natural ingredient of the plants in the forest.

　
In the forest there is no floating harmful bacteria.

If smoke, exhaust gas and other polluted air come into the forest, they shall be purified at once.

　
Phytoncide consists of more than 130 kinds of volatile ingredients given off  by unmoving plants against harmful insects and bacteria.

　
We are human beings, born from the nature same as plants and animals.
Diseases of today such as atopy dermatitis, pollen allergy and others are becoming popular due to separation between human beings and the nature, aren't they?
Phytoncide is a mercy of the nature to keep our health and safe environment.
　

For your ref.: Phytoncide from Wikipedia

Phytoncides are antimicrobial allelochemic volatile organic compounds derived from plants. The word, which means “exterminated by the plant”, was coined in 1937 by Dr. Boris P. Tokin, a Russian biochemist from Leningrad University. He found that some plants give off very active substances which prevent them from rotting or being eaten by some insects and animals. Various spices, onion, garlic, tea tree, oak and pine trees, and many other plants give off phytoncides. Oak contains a substance called greenery alcohol; garlic contains allicin and diallyl disulfide; and pine contains alpha-pinene, carene, myrcene and other terpenes. More than 5000 volatile substances defend the surrounding plants from bacteria, fungi and insects. Phytoncides work by preventing the growth of the attacking organism.
They are widely used in Russian, Ukrainian, Chinese and Japanese medicine, including holistic medicine, aromatherapy, and veterinary medicine.
In Taiwan, South Korea and Japan, people commonly engage in so-called forest bathing to breathe in phytoncides emitted by plant and trees, in order to improve their health.