"Cellular senescence is one of the causes of degenerative aging. Normal somatic cells in adults become senescent at the end of their replicative life span, when they reach the Hayflick limit on cell divisions, or in response to damage or a toxic environment. Most such cells self-destruct or are destroyed by the immune system, but some linger to cause problems, ever more of them over the years. A senescent cell generates a mix of signals known as the senescence-associated secretory phenotype (SASP) that promotes inflammation, damages surrounding tissue structures, and alters the behavior of nearby cells for the worse. Senescence isn't all bad, however: in limited doses, it helps to lower the risk of cancer by shutting down those cells most at risk. It also occurs during wound healing and embryonic development, and plays necessary roles in both of those processes. Nonetheless, cellular senescence helps to kill us as we age, and as more of these cells accumulate in tissues, their presence speeds the progression of many age-related diseases."