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.
Every cell in your body has an emergency brake: if it sustains too much damage, it can permanently stop dividing. Those are senescent cells. They no longer respond to growth signals, and they do not die off in the normal way either. That combination, being permanently halted yet continuing to live, is what makes them remarkable.
Cells enter this state because of DNA damage, because of telomere shortening (the protective caps at the ends of your chromosomes become a little shorter with every cell division), or because a gene that can cause cancer suddenly switches on. It is therefore an emergency response to a threat. In the short term that is clever: a damaged cell that stops dividing cannot form a tumour.
The problem starts when those cells accumulate. Senescent cells secrete large quantities of inflammatory substances, a mixture of signalling molecules, enzymes and other compounds that stir up their surroundings. This produces a smouldering, chronic inflammation that persists for years. Research links that accumulation to atherosclerosis, osteoarthritis, chronic lung disease and an increased cancer risk. Whether this is always directly the cause in humans or is partly a consequence as well has not yet been fully resolved, but the evidence is strong.
Senescent cells also actively survive: they switch on protective mechanisms that prevent them from dying, even when they carry considerable damage. That makes them stubborn. In the brain they accumulate with ageing and in diseases such as Alzheimer's, but there the causal role is still unclear.
Yet senescence is not a purely bad thing. During embryonic development and during tissue repair after injury, senescent cells play a useful role, and they also form a barrier against cancer. This makes it difficult to simply clear them all away: too little senescence can lower the threshold for cancer. Treatments that target senescent cells specifically are being actively developed, but are not yet part of everyday clinical practice.
Based on multiple reviews and mechanistic studies (PMID: 30648461, 29477613, 33328614, 32800277, 35015337, 36732079, 38583577, 38030088). The causal evidence in humans is strongly plausible for most age-related diseases but has not yet been fully proven through interventions in humans. The brain findings are preliminary and associative.
What exactly does senescence do to your cells as you age?
Senescent cells stop dividing, accumulate with age and cause damage throughout the body through a constant stream of inflammatory substances. They are both a protector (a brake on cancer) and a cause of damage, and that makes targeted intervention more complex than it appears.
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 as a protection against damage and cancer, but the accumulation of such stopped cells contributes over the years to inflammation and age-related diseases. Drugs that target this are promising in animal research, but are not yet ready for use outside clinical studies.
Why do cells lose their ability to repair themselves over time?
Cells lose their repair capacity through a combination of declining energy stores, impaired DNA repair and the accumulation of 'burned-out' cells that secrete inflammatory substances. These are well-supported mechanisms, although it is still too early to act on them through supplements or therapies.
Why do damaged proteins accumulate in your cells as you age?
As you age, several systems that clear away damaged proteins weaken simultaneously and amplify each other's failure. This is one of the central mechanisms behind age-related diseases, but how to stop it in a targeted way is still actively being researched.
How does air pollution damage your cells from the inside?
Air pollution damages your cells from the inside through oxidative stress: fine particulate matter causes an excess of harmful oxygen molecules that attack your DNA, energy factories, and immune system. Protection begins with limiting exposure, because the damage occurs at the cellular level.