aging

Introduction
Biological theories of aging
- Genetic theories
- Nongenetic theories
  - Wear-and-tear theory
  - Cross-linking theory
  - Autoimmune theory
  - theory
  - Oxidative damage theory
  - Psychosociological theory
Natural history of aging
- Reproduction and aging
- Species differences in longevity and aging
- The inheritance of longevity
Senescence in mammals
- Changes in body composition, metabolism, and activity
- Changes in structural tissues
- Tissue cell loss and replacement
- Mammalian cell cultures
- Changes in tissue and cell morphology
Aging at the molecular and cellular levels
- Aging of genetic information systems
- Aging of the immune system
- Aging of neural and endocrine systems
Internal and external causes of aging
- External environmental agents
  - Ionizing radiation
  - Temperature
  - Physical wear of nonrenewable structures
  - Infectious disease and nutrition
- Internal environment: consequences of metabolism
Anti-aging and longevity research
- Antioxidants
- Calorie restriction and longevity
- Sirtuins
- Rapamycin
- Stem cells
- Genetics and life span

References & Edit History Quick Facts & Related Topics

Images & Videos

Know how unlike humans some organisms like naked mole rats, rock fish, lobsters, and bristlecone pines can pause their aging process

Know how telomeres protect the ends of the chromosomes and over a while, it causes cellular aging

Golden wheat stalks in a field, shown in close-up with rolling hills and a blue sky in the background.

A chart compares the maximum life spans of various animals, using icons and color coding for mammals, birds, other vertebrates, and invertebrates. Lifespans range from the mayfly at less than a year to the Greenland shark at 500 years, with humans, elephants, whales, birds, and reptiles shown at various points along the timeline. Measurement intervals are marked in years, with a key at the bottom explaining the color categories.

A group of senior citizens sits in chairs, smiling and holding their hands together in a prayer pose during an exercise class.

At a Glance

aging summary

aging

life process

Also known as: ageing

Written by

Petra SimicAll

Fact-checked by

Britannica Editors

Last updated

Oct. 19, 2026 •History

aging, progressive physiological changes in an organism that lead to senescence, or a decline of biological functions and of the organism’s ability to adapt to metabolic stress. Aging takes place in a cell, an organ, or the total organism with the passage of time. It is a process that goes on over the entire adult life span of any living thing. Gerontology, the study of the aging process, is devoted to the understanding and control...

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