Aging is a progressive decline in physiological function driven by interconnected biological processes. At the cellular level, damage accumulates in DNA, proteins and lipids. Cells experience genomic instability, impaired DNA repair and epigenetic drift, which together alter gene expression and cell behavior. Telomeres, the protective ends of chromosomes, shorten with each cell division, eventually triggering cell cycle arrest or senescence.

Cellular senescence is a key feature of aging. Senescent cells stop dividing but remain metabolically active, secreting inflammatory molecules, proteases and growth factors. This senescence associated secretory phenotype disrupts tissue structure, promotes chronic inflammation and impairs regeneration. Experiments in mice show that selectively removing senescent cells can delay multiple age related disorders and extend healthy lifespan, suggesting senolytic drugs as a promising therapeutic approach.

Mitochondrial dysfunction also contributes to aging. Damaged mitochondria produce excess reactive oxygen species, creating a vicious cycle of oxidative damage. Over time, this undermines energy production, especially in high demand tissues such as heart, brain and muscle. Declining proteostasis, including misfolded and aggregated proteins, further stresses cells and is linked to neurodegenerative diseases.

Stem cell exhaustion reduces the body’s ability to repair tissues. Combined with systemic low grade inflammation and altered nutrient sensing pathways like insulin and mTOR, this shifts the internal environment toward frailty and disease. Interventions that modulate these pathways, such as caloric restriction mimetics or mTOR inhibitors, can extend lifespan and healthspan in model organisms.

Overall, aging emerges from multiple reinforcing mechanisms. Current research aims to target these mechanisms directly, with the goal of delaying age related diseases and preserving function rather than merely extending years of life.