Hormesis is defined as a dose-responsive phenomenon typified by low-dose stimulation and high-dose inhibition. It has been identified as an overcompensation response for mild environmental stress related to the body's intrinsic ability for self-maintenance and repair. In fact, the beneficial effects of mild stress on aging and longevity have been examined for long time. Thus, beneficial hormetic effects of repeated mild heat stress on aging human cell cultures in terms of their structural and functional integrity have been demonstrated. Other mild stresses have also been reported to defer aging and stimulate longevity in experimental animals. These include mild hyperthermia, irradiation, hyper-gravity, exercise and caloric restriction, as well as chemical agents such as heavy metals, pro-oxidants, acetaldehyde, alcohols, and resveratrol. In experimental animals, mild dietary stress without malnutrition postpones the majority of age-related physiological changes, prevents aging disease, and extends lifespan.