Aging and Senescence

The gradual decline of function in later life. Aging is the passage of time; senescence is the biological wearing-down that accompanies it.

What is happening

• At the cellular level — cells accumulate damage, divide less readily, and some enter a worn-out “senescent” state; repair processes slow.
• System by system — bone is lost faster than it is rebuilt, muscle mass declines, blood vessels stiffen, the immune system weakens, and the senses dull.
• Reduced reserve — organs lose their spare capacity, so the body recovers more slowly from stress, illness, and injury.

Why it matters

Aging is the single largest risk factor for many diseases — heart disease, dementia, cancer — yet the rate of decline varies enormously between individuals. Understanding why is one of the most active questions in biology, and separating unavoidable aging from preventable damage is central to it.