Cellular senescence

Senescent cells accumulate across many organs and tissues with aging, but also in younger people at sites of chronic conditions. These senescent cells rarely, if ever, divide, but are active: they resist dying. Some produce a range of factors that damage cells, interfere with progenitor function, and spread senescence to previously normal cells. Senescent cells are normally removed by the immune system, but above a threshold burden, they can resist immune clearance and spread faster than the immune system can keep up.