What is ageing?

In brief: Ageing is the gradual deterioration of the body's natural functions over a lifetime. As this occurs, damage accumulates in cells, tissues and organs, and becomes harder to repair over time. This increases the risk of many diseases. The rate at which this process occurs varies from person to person.

The term ‘ageing’ is defined in ageing research as the gradual decline in our body’s natural functions. This leads to an increase in functional limitations, greater susceptibility to disease and a higher risk of death. Ageing is the main risk factor for numerous diseases such as cardiovascular disease, diabetes, neurodegenerative diseases and cancer. This loss of function is caused by the accumulation of damage to genetic material, cells and tissues, which becomes increasingly difficult to repair as we get older (see ‘How do we age?’). Ageing is a complex process that takes place at a molecular level within our cells, tissues and organs. (Lopez-Otin C et al., 2013)

Age and ageing are two different things. Age is, first and foremost, a number and describes how many years have passed since birth. Ageing, on the other hand, is a biological process that can be observed, measured and scientifically described (see ‘How can you measure biological age?’).

Ageing does not proceed at the same rate in all individuals, and there are also significant differences in nature. Whilst fruit flies usually live for only a few weeks and mice for a few years, bowhead whales are thought to be able to live for over 200 years (Firsanov D et al., 2025). Organisms such as naked mole-rats, long-lived turtle species or freshwater polyps of the genus Hydra are also of interest in ageing research, as they exhibit exceptional characteristics in terms of longevity, regeneration or age-related functional decline (Ma S and Gladyshev VN, 2017; Tian X et al., 2017). Such examples from comparative ageing research help to identify biological mechanisms that may influence ageing processes.

Updated on 26 June 2026