Aging biology has a strange villain: cells that stop dividing but refuse to die. These are called senescent cells — sometimes nicknamed "zombie cells" — and they accumulate steadily in tissues throughout the body as you age.
Under normal conditions, senescent cells play a short-term role: they send out chemical signals that recruit the immune system to remove them. But when that clearance fails — as it increasingly does with age — they persist. And they leak. The toxic cocktail they continuously secrete is called the senescence-associated secretory phenotype, or SASP: a mix of inflammatory proteins, enzymes, and growth factors that damage surrounding tissue, promote chronic inflammation, and accelerate the aging of neighboring healthy cells.
