What exactly does senescence do to your cells as you age?
Senescent cells stop dividing and secrete inflammatory substances that damage tissues over time. They are necessary in youth, but when they accumulate they accelerate ageing and disease.
When a cell becomes senescent, it permanently stops dividing. Normally a cell responds to signals from the body to grow and multiply, but a senescent cell has become deaf to those signals. This is initially useful: if a cell is at risk of veering toward cancer, it gets locked down in this way. At a younger age, that brake is an important protective mechanism.
The problem is what the stopped cell does next. It does not become passive, but instead begins actively secreting inflammatory substances, including the signalling molecules interleukin-6 and interleukin-8. This pattern of secretion is called the SASP. Those substances reach neighbouring cells and tissues and put them in a mild but persistent state of inflammation. It takes several days after DNA damage, incidentally, before a senescent cell begins producing the full quantity of these substances.
As you get older, senescent cells accumulate in your tissues while the body becomes less effective at clearing them. That accumulation causes a smouldering chronic inflammation that contributes to age-related diseases and to the decline in the ability of tissues to repair themselves. As a result, tissue finds it increasingly difficult to renew itself after damage.
There is also a paradox. Although the senescent cell itself does not become cancerous, the substances it secretes into the surrounding environment can actually drive pre-malignant cells toward growth and aggressiveness. The protection of one cell therefore comes at the expense of the safety of its neighbours. That tension worsens when tumour-suppressing mechanisms within the cell itself fail, or when certain cancer-driving genes are active.
Senescence is not purely negative. During embryonic development and in short-term tissue repair, senescent cells are in fact necessary for proper construction and restoration. The problem arises when they linger too long. Metabolic problems such as obesity also accelerate the formation of new senescent cells, while those cells in turn further disrupt metabolism through the substances they secrete, creating a downward spiral.
This answer draws on several review studies that summarise the existing literature, including work on the molecular mechanisms of senescence, the SASP, and the role of senescence in cancer and ageing. There is no single study in which people were randomly assigned to test the consequences of senescence; many of the mechanistic insights come from laboratory and animal research. The core of the story, permanent cell-cycle arrest and inflammatory secretion, is well supported and broadly accepted in the literature. The tumour paradox and the role in metabolic disease are somewhat less certain but plausible on the basis of multiple sources.
What are senescent cells and why are they bad for you?
Senescent cells are damaged cells that stop dividing but continue to live and chronically inflame their surroundings. They accumulate as you age and are strongly linked to age-related diseases, but because they also play a protective role, simply clearing them all away is not an option.
What do zombie cells do to your ageing?
Zombie cells accumulate as you age and accelerate ageing through inflammatory signals; how to tackle them is promising but still very much under investigation.
Why do some cells stop dividing as you age?
Cells stop dividing because their chromosome tips wear down and they accumulate DNA damage: a protective mechanism that in later life becomes harmful precisely because the stalled cells build up. Treatments that address this are still under active investigation and are not ready for self-application.
Does clearing out senescent cells with senolytics help against ageing?
Senolytics show impressive results in animal studies, but in people the evidence is too thin for use outside a research setting. Self-medicating with Dasatinib is inadvisable given its side effects and the risks around tumour growth.
Does chronic inflammation accelerate the ageing of your cells?
Chronic inflammation demonstrably accelerates cellular ageing through a negative spiral that is difficult to break. The best evidence-based approach to tackling that spiral is through lifestyle factors that dampen low-grade inflammation, such as sufficient exercise and a diet low in ultra-processed products.
What is the role of inflammation in cellular ageing?
Inflammation and cellular senescence reinforce each other in two vicious cycles, leading to tissue damage and age-related diseases. Both protecting your cells against oxidative damage (think sun protection and lifestyle) and future targeted therapies aim to break this cycle.