Cellular senescence
Old cells refuse to leave
A damaged cell has two honourable options: repair itself, or die. A third kind does neither. It stops dividing, refuses to leave, and spends the rest of your life shouting inflammatory signals at the healthy cells around it. A few are useful — that is one way the body stops a damaged cell becoming a tumour. Too many, and the whole tissue ages around them.
Exercise clears some of them, which is one more reason it turns up on nearly every entry here. Senolytics — drugs that persuade these cells to finally die — are the most watched idea in the field, and they are in human trials, not on a shelf. Anything sold to you today as a senolytic supplement is running ahead of what has actually been shown.
The science, in one sentence
Damaged cells stop dividing but do not die, and broadcast an inflammatory signal into the tissue around them.