Everyone has senescent cells. They're present in the skin, the brain, muscles and heart. Every day, your body faces stress — poor sleep, sun exposure, pollution, psychological strain — and it affects your cells. Most repair themselves. Some die and are replaced. But others do neither. They stop functioning, yet refuse to disappear. Researchers call them senescent cells. In popular science, they've earned another name: zombie cells.
Why do we age?
For a long time, aging was considered something that simply happened — an inevitable decline without a clear cause. That's no longer true.
Over the past two decades, researchers have identified twelve biological mechanisms that drive aging. They're called the hallmarks of aging, first published in 2013 by an international research team — and updated in 2023 in the journal Cell. Among them: telomere attrition, mitochondrial dysfunction and genomic instability. And one of the most extensively studied: cellular senescence.
This means aging isn't random. It has specific, identifiable causes — and cellular senescence is one of them.
What happens inside a senescent cell?
A healthy cell divides, performs its function, and dies when it's no longer needed. This is called apoptosis — programmed cell death. It's a natural and necessary process.
A senescent cell has lost that ability. It doesn't divide, but it doesn't die either. Instead it remains — enlarged, dysfunctional and metabolically active. And that's not the worst part.
Senescent cells secrete a cocktail of inflammatory signals, enzymes and other molecules. Researchers call it SASP — senescence-associated secretory phenotype. These signals affect surrounding healthy tissue. Think of a mouldy piece of fruit in a bowl of fresh ones. It just sits there — but over time, everything around it is affected.
SASP drives chronic, low-grade inflammation. Not the kind you notice like a swollen ankle, but a silent burden on tissues and organs, year after year.
Why does it get worse with age?
In a young body, the system works. The immune system identifies senescent cells and clears them — typically within days or weeks. The balance holds.
But the immune system isn't immune to aging. It's affected by the very process it's meant to protect against. Immune cells themselves become senescent — losing their ability to identify and eliminate the cells that should be gone. Researchers call it immunosenescence.
The result is a vicious cycle: senescent cells accumulate, burdening the immune system, which in turn loses its ability to clear them. The accumulation accelerates — particularly after 60.
What does the research say?
Interest in cellular senescence has exploded over the past decade. Researchers at institutions including Mayo Clinic, MIT and University of Texas Health have driven the field forward. Studies have mapped how senescent cells contribute to age-related conditions — from reduced physical function to altered tissue structure.
In 2018, a study published in EBioMedicine compared ten naturally occurring flavonoids and their ability to target senescent cells. The results showed clear differences in efficacy between the compounds.
One of the most important insights from the research: senolytic compounds — substances that in preclinical studies have demonstrated the ability to target senescent cells — are not administered daily. They're given as short, intensive interventions followed by rest. This intermittent approach, not daily dosing, has become the dominant strategy in clinical research.
The field is still young. Most studies are preclinical — conducted in cell cultures and animal models. But clinical trials are underway, and the direction is clear: cellular senescence has moved from an academic concept to one of the most active areas of aging research.
Why does it matter?
Senescent cells aren't a footnote in biology. They're one of the twelve defined causes of why we age. They drive inflammation, burden the immune system and affect surrounding tissue — silently, gradually and cumulatively.
You don't notice it. And that's the point.
Read about the research behind the senolytic protocol →
Sources: López-Otín et al., "Hallmarks of Aging: An Expanding Universe," Cell, 2023. Zhu et al., "New agents that target senescent cells," EBioMedicine, 2018. Kirkland & Tchkonia, "Cellular Senescence," Mayo Clinic, 2017.
