Your Skin Doesn't Just Get Older. Its Cells Change
For a long time, the story of skin ageing was mostly a story of things being lost. Collagen declines, elastin becomes less effective, hyaluronic acid changes, the extracellular matrix becomes less organised, and decades of ultraviolet exposure add another layer of damage. The result is familiar: thinner, drier, less elastic skin, slower repair and increasingly persistent wrinkles.
All of that is still true. But another layer of the biology is becoming increasingly difficult to ignore: the cells themselves change their behaviour as skin ages.
One of the most interesting changes is cellular senescence.
Senescence is often described as a state in which a cell permanently stops dividing. That is part of the story, but it is not the whole story. Senescent cells can also undergo changes in metabolism, gene expression and signalling. Some develop what is known as the senescence-associated secretory phenotype, or SASP, releasing inflammatory cytokines, chemokines, growth factors and enzymes that can alter the tissue around them.
That changes the question of skin ageing quite a bit. Instead of asking only why older skin produces less collagen, researchers are increasingly asking what happens when the cells responsible for maintaining the skin's structure become dysfunctional themselves.
And perhaps the most interesting question is what happens to the neighbouring cells and tissue environment when that occurs.
Senescence is not simply "zombie cells"
The popular description of senescent cells as "zombie cells" is catchy, but it makes the biology sound much simpler than it is.
Senescence is not inherently pathological. Cells can enter senescence in response to things such as DNA damage and oncogenic stress, and the resulting growth arrest can be protective because it prevents damaged cells from continuing to proliferate. Senescence is also involved in physiological processes such as wound healing and tissue remodelling.
The problem may arise when senescent cells persist, accumulate or develop a particularly disruptive secretory phenotype. Instead of disappearing after their useful role is complete, they can remain in the tissue and continue releasing signals that alter inflammation, extracellular-matrix turnover and the behaviour of nearby cells.
That is why the modern view of senescence is becoming less about "bad cells that should all be killed" and more about cell state, context and communication.
A 2025 review in Ageing Research Reviews brought together the emerging evidence linking cellular senescence with skin ageing and dermatological disease. It also reviewed the growing field of senolytics and senomorphics, while emphasising that senescence is heterogeneous and that different cell types can develop different phenotypes and functions. Thau et al., 2025
What is actually happening in human skin?
One of the most interesting recent studies looked directly at this question using single-cell RNA sequencing and spatial transcriptomics of human skin.
Yu and colleagues examined senescence across different cellular populations in human epidermis and dermis. Rather than treating skin as one uniform tissue, they were able to identify individual cell populations and examine the molecular programmes associated with senescence in each of them. Yu et al., 2025
The findings make the story much more interesting than simply saying that "senescent cells increase with age."
Photoaged skin showed stronger senescence-associated signatures than chronologically aged skin, suggesting that environmental stress, particularly long-term UV exposure, may contribute substantially to the senescent phenotype. Different cell populations also appeared to respond differently. Senescent melanocytes showed changes in pathways associated with melanin production, while senescent dermal fibroblasts showed reduced expression of genes involved in collagen and elastic-fibre synthesis.
The researchers also found that senescent cells had a tendency to cluster, particularly in photoaged skin, and developed a skin-specific senescence gene signature known as SenSkin.
That represents an important shift in how researchers are thinking about the problem. Instead of asking whether ageing skin contains senescent cells, the question becomes which cells have become senescent, where are they located, and what are they doing?
That is a much more useful biological question.
Why fibroblasts matter
For skin regeneration, the fibroblast findings are particularly interesting.
Dermal fibroblasts help maintain the extracellular matrix, producing and organising collagen, elastin and other structural components. They also respond continuously to mechanical and biochemical signals from the surrounding tissue.
If a population of fibroblasts becomes senescent, loses some of its ability to maintain the matrix and simultaneously begins producing inflammatory or matrix-modifying signals, the result may be more than a simple reduction in collagen production.
It could become a feedback loop.
The tissue becomes less capable of maintaining its matrix. The surrounding signalling environment becomes more inflammatory. Repair becomes less efficient. The altered extracellular matrix then changes the signals experienced by other cells.
That does not mean every ageing fibroblast is senescent, nor that senescence explains all collagen loss. Skin ageing remains a complicated combination of intrinsic ageing, UV exposure, inflammation, mechanical forces, hormonal changes and many other processes.
But the human data make senescent fibroblasts a plausible contributor rather than merely a theoretical one. Yu et al., 2025
Photoaging may be a major part of the story
The relationship with photoaging is particularly interesting.
UV radiation produces DNA damage and oxidative stress, and repeated exposure over decades gives cells repeated opportunities to accumulate damage or enter altered states. The emerging evidence suggests that some of that stress may eventually manifest as an increasing burden of senescence-associated cells.
This gives sun protection another layer of importance beyond the familiar prevention of collagen breakdown and pigmentation.
You are not only protecting the extracellular matrix that is already there. You may also be reducing one of the environmental pressures that contributes to the development of dysfunctional cellular states in the first place.
The distinction between chronological ageing and photoaging is therefore important. Skin does not necessarily age simply because time passes; it ages because its cells are continuously responding to their environment.
Senolytic or senomorphic?
Once researchers began treating senescence as a potential therapeutic target, two broad strategies emerged.
Senolytics aim to eliminate senescent cells. The idea is that some senescent cells become unusually dependent on certain survival pathways, allowing researchers to target those pathways and push the cells toward apoptosis.
One of the best-known examples is the combination of dasatinib and quercetin, usually referred to as D+Q. Early human studies have shown that senolytic treatment can alter senescence-associated markers in tissues. In a small pilot study involving people with diabetic kidney disease, a short course of D+Q was associated with reductions in several senescence-associated markers in adipose tissue and skin, together with changes in circulating inflammatory and matrix-related factors. Justice et al., 2019
That was an important proof of concept because it moved the field beyond purely animal research.
But it was not a cosmetic skin-rejuvenation trial, and it does not establish D+Q as a treatment for skin ageing.
The other approach is the senomorphic strategy.
Rather than killing senescent cells, the goal is to alter their behaviour. That might mean suppressing harmful SASP signalling, changing inflammatory pathways or modifying dysfunctional metabolic states while leaving the cells themselves alive.
This distinction matters because senescence itself is not necessarily something the body wants to eliminate indiscriminately.
A senomorphic treatment might therefore aim for something much more subtle: not necessarily turning an old cell back into a young one, but making the cell less disruptive to the tissue around it.
Rapamycin and the idea of modifying senescence
Rapamycin has attracted considerable interest in ageing research because of its effects on the mTOR pathway, cellular growth and metabolism. It has also been investigated in human skin as a potential way of modifying age-associated cellular changes.
A small randomized exploratory study published in 2019 tested topical rapamycin in adults over 40. The investigators reported reductions in the senescence-associated marker p16 and increases in collagen VII among participants who completed the study. Choi et al., 2019
The result is interesting, but the limitations matter. The study was small and had substantial attrition, and it does not establish that topical rapamycin broadly reverses skin ageing.
This is a recurring problem in the field. The underlying mechanism can be biologically interesting while the clinical evidence remains far from sufficient to support broad treatment claims.
We should be careful about the word "reverse"
It is tempting to describe senotherapeutic approaches as "reversing ageing cells."
But the biology is more complicated.
If senescence is partly a protective response to cellular damage, then forcing a damaged cell back into proliferation would not automatically be desirable. A useful senomorphic therapy may instead be one that suppresses the harmful features of persistent senescence while preserving appropriate cellular checkpoints.
In other words, the goal may not be:
old cell → young cell
or:
senescent cell → eliminated cell
It may instead be:
senescent cell → less inflammatory, less disruptive cell
That is a subtler target, but potentially a much more rational one.
Senescence may be a problem of the whole tissue
The idea becomes even more interesting when you look outside the skin.
A 2026 Nature Cell Biology study examining DNMT3A-mutant clonal haematopoiesis found that abnormal blood-cell clones could induce senescence in mesenchymal stromal cells in the bone marrow. Those senescent stromal cells then appeared to support the abnormal clones through altered signalling. In mice, removing senescent non-haematopoietic cells reduced the burden of clonal haematopoiesis and delayed progression toward myeloid neoplasia.
The broader lesson is important: senescent cells may matter not simply because they are dysfunctional themselves, but because they can reshape the microenvironment around them.
That idea is highly relevant to skin.
A senescent fibroblast does not exist in isolation. The surrounding cells respond to the signals it produces, while those responses can alter the extracellular matrix and the behaviour of other cells.
The future of senescence research may therefore be less about identifying "bad cells" and more about understanding pathological cellular ecosystems.
So do we need senolytics?
Not necessarily.
The fact that senescent cells contribute to ageing does not mean that everyone should be taking a senolytic or using a senomorphic treatment.
We still lack a clinically validated way to measure an individual's burden of pathological senescence in skin and then determine what intervention would be appropriate. We also do not yet know which senescent cells should be removed, which should be modulated and which may still be serving useful biological functions.
This is one reason the newer research using single-cell and spatial technologies is so important. It moves the field closer to identifying cell type, location and function, rather than treating every senescence-associated cell as biologically equivalent.
The likely future is therefore much more specific: specific cell populations, specific tissues, specific senescence-associated pathways and potentially specific interventions for specific stages of disease or ageing.
Where this leaves us
The science of skin ageing is shifting.
For years, the major question was how to replace what ageing skin had lost: collagen, hydration, volume or structural support.
Now another question is emerging alongside it:
What if part of the problem is not simply what the skin has lost, but what some of its cells have become?
We are beginning to see convincing human evidence that senescence-associated changes occur in ageing skin, and that those changes differ between cell populations. We are learning that photoaging may be particularly important, that senescent fibroblasts can be associated with reduced matrix production, and that senescent cells can influence the tissue around them.
At the same time, senolytic and senomorphic strategies are moving from the laboratory toward early human studies.
But that is where a little scepticism is useful.
The biology of senescence is increasingly compelling.
The clinical science of senotherapeutics is still developing.
And those are not the same thing.
For me, the most interesting question is not whether we will eventually have a cream, injectable or drug labelled "anti-senescence."
It is whether we will eventually become good enough at reading aged tissues to know which cells are causing the problem, what they are signalling, and whether they should be removed or simply encouraged toward a less harmful state.
That would be a very different kind of anti-ageing medicine.
And perhaps a much more interesting one.
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---Key papers
Yu GT, et al. (2025). Mapping epidermal and dermal cellular senescence in human skin aging. Aging Cell, 24(1), e14358. https://doi.org/10.1111/acel.14358
Thau H, et al. (2025). Senescence as a molecular target in skin aging and disease. Ageing Research Reviews, 105, 102686. https://doi.org/10.1016/j.arr.2025.102686
Idda ML, et al. (2020). Survey of senescent cell markers with age in human tissues. Aging, 12(5), 4052–4066. https://doi.org/10.18632/aging.102903
Choi YJ, et al. (2019). Topical rapamycin reduces markers of senescence and aging in human skin. GeroScience. https://doi.org/10.1007/s11357-019-00113-y
Justice JN, et al. (2019). Senolytics decrease senescent cells in humans. EBioMedicine, 47, 446–456. https://doi.org/10.1016/j.ebiom.2019.08.069
Zonari A, et al. (2024). Clinical investigation of topical OS-01 for skin rejuvenation. Journal of Cosmetic Dermatology. https://doi.org/10.1111/jocd.16242
This article discusses emerging research in cellular senescence and senotherapeutics. It is not a recommendation to use senolytic, senomorphic or investigational therapies.