Hormesis theory

A theory that has been gaining acceptance recently is that many chemicals have beneficial effects at very low doses and may perhaps stimulate protective mechanisms, and that as the dose increases the effects become adverse. This is known as hormesis and may occur as a result of more than one exposure to a chemical (see box). ... 

Parsons, P. A. 2007. The ecological stress theory of aging and hormesis An energetic evolutionary model. Biogerontology 8 233-242. 

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