Xenohormesis is a hypothesis that states that by responding to various environmental conditions, plants produce bioactive compounds, which can be harvested from plants by mammals. These compounds are used to increase stress adaptation and pathway in animals or humans. The compounds that turn on the adaptive responses of plants are polyphenols. There are studies linking various properties of polyphenols with prevention of certain chronic and neurodegenerative diseases. It is important to conduct more research in investigating the effects of phenols and polyphenols under certain conditions.