Cells become senescent in response to a toxic, damaging environment. This is a first line of defense against the possibility of cancer. Senescent cells cease replication and begin to secrete a potent inflammatory mix of signals that usually serves to attract immune cells to destroy them, if they don't manage to self-destruct via their own programmed cell death processes. Unfortunately, the immune system becomes ever less functional with age, and thus lingering senescent cells will accumulate in ever greater numbers. This is probably why many of the progressive lung conditions arising from a toxic environment, such as that produced by smoking, tend to arise at a later age.

Researchers here show that a sizable fraction of the pulmonary dysfunction arising from smoking is mediated by the actions of senescent cells in lung tissue, which in turn suggests that senolytic therapies presently under development for age-related diseases will greatly reduce the consequences of smoking and other forms of particulate exposure. Not that is will ever make it smart to stab yourself repeatedly, just because you know that hospital staff can patch up the injury.

Link: https://doi.org/10.1038/s42003-019-0532-1