Hormesis (from the Greek word "normao", meaning "to excite") is a biological phenomenon in which a beneficial effect (such as increased lifespan, stress tolerance, or growth) results from exposure to low doses of a potentially harmful substance or condition (such as heat, radiation, or toxins). Hormesis is characterized by a dose-response relationship, in which a low dose of a stressor produces a positive effect, while a high dose produces a negative effect. Hormesis is studied in different areas of biology, such as in the response of cells to environmental stressors or toxins.
Some researchers have proposed that hormesis may play a role in the aging process. Certain types of cellular stress, such as caloric restriction and exposure to mild toxins, have been shown to extend lifespan in a variety of animal models. Mild dietary restriction without malnutrition has demonstrated able to prevent the onset or to decrease the severity of several age-related diseases, such as cancer, neurodegeneration or cardiovascular diseases. Heat-shock or cold-shock responses are also considered to be hormesis mechanisms.
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