Nonaging

Nonaging is a term used in biogerontology to describe a situation in which aging is absent or negligible. In practice, it refers to an organism or population in which age does not produce the expected time-dependent decline in survival or reproduction. It is distinct from immortality, because nonaging does not preclude death from accident, disease, or environmental hazards; it simply means that biological aging does not measurably increase risk with advancing age.

Most animals exhibit senescence, with mortality risk and functional decline rising with age. Some organisms have patterns described as negligible senescence, where these age-related changes are minimal or slow over long lifespans. Reported examples include certain stable cnidarians such as some hydra species and some planarians, which maintain tissue renewal and regenerative capacity. Claims about truly nonaging organisms, such as certain jellyfish that can revert to earlier life stages, are controversial and not universally accepted as evidence of complete nonaging; many such cases reflect remarkable regenerative abilities rather than a complete lack of aging.

In human biology and in most vertebrates, nonaging has not been demonstrated. Research on aging aims to understand mechanisms of aging and to promote healthspan, rather than to produce genuine nonaging. The concept remains largely theoretical and is used mainly to frame discussions of longevity and population dynamics.