Most cells in the body can divide and create new cells.
This helps replace cells that are old, worn out or damaged.
But sometimes a cell becomes too damaged to continue dividing safely. To protect the body, it receives a signal telling it to stop making new copies of itself.
The cell does not necessarily die. It may remain in the tissue and continue to be active.
This state is called cellular senescence.
The name sounds complicated, but the basic idea is simple:
the cell has stopped dividing, but it has not completely disappeared.
At first, this can be useful.
Stopping a damaged cell from dividing may prevent it from passing its damage on to new cells. This protective response may also support wound healing and help the body deal with an injury.
The problem begins when growing numbers of these cells remain in the body for a long time.
They are known as senescent cells.
Senescent cells can release chemical signals that affect the cells around them. Some of these signals may increase ongoing inflammation and make it harder for nearby tissues to work and repair themselves normally.
For this reason, the gradual build-up of senescent cells may contribute to slower healing, weaker tissue function and some of the changes associated with ageing.
This does not mean that every senescent cell is harmful.
Cellular senescence is a natural protective mechanism. It becomes more of a problem when the body is no longer able to remove these cells efficiently after they have completed their useful role.
Other age-related changes may also cause cells to enter this state.
Damage to DNA, very short telomeres and problems with energy production can all make it unsafe for a cell to continue dividing.
Scientists are studying medicines called senolytics, which are designed to remove some senescent cells.
This research is promising, but these medicines are not currently a routine anti-ageing treatment for healthy people. Scientists also do not want to remove every senescent cell, because some of them perform useful functions.
There is no simple test that can count all senescent cells throughout the body.
For now, the most practical approach is to reduce the damage and long-term stress placed on cells.
Regular physical activity, adequate sleep, not smoking and controlling blood pressure, blood glucose and other health risks help create better conditions for cells and tissues.
Healthy ageing does not mean preventing every cell from becoming senescent.
It means helping the body maintain the balance between stopping damaged cells, removing them when they are no longer needed and allowing healthy tissues to continue renewing themselves.
