The result of a combination of natural, largely genetically programmed changes occurring in all body systems. Diseases or injuries may influence these changes, which impair the body's HOMEOSTASIS; environment and lifestyle also affect the ageing process.

The effects of ageing include: wrinkling of the skin due to a loss of elastic tissue; failing memory (especially short term); and a reduced ability to learn new skills, along with slowed responses – changes caused by the loss of or less efficient working of nerve cells; the senses become less acute; the lungs become less efficient, as does heart muscle, both causing a fall in exercise tolerance; arteries harden, resulting in a rise in blood pressure and poor blood circulation; joints are less mobile, bones become more brittle (OSTEOPOROSIS) and muscle bulk and strength are reduced; the lens of the EYE becomes less elastic, resulting in poorer sight, and it may also become opaque (CATARACT). There is a cessation of MENSTRUATION in females (see MENOPAUSE).

In 2014, there were nearly 15,000 centenarians in the UK and 500,000 persons over the age of 90. This longevity is attributed to a particular gene (see GENES) slowing the ageing process. Interestingly, many of those living to 100 retain the mental faculties of people in their 60s, and examination of centenarians’ brains show that these are similar to those of 60-year-olds. (See MEDICINE OF AGEING; CLIMACTERIC.)