The 'hallmarks of aging' organise the field. They are a checklist, not a theory.

If you read anything about the biology of ageing, you will quickly meet the "hallmarks of aging" — a list of cellular and molecular processes said to drive the whole business of growing old. The framework began with a 2013 paper in Cell that enumerated nine hallmarks [s1] and was updated in 2023 to twelve [s2]. It is worth understanding what the list is and, just as importantly, what it is not: it is a shared inventory of what changes with age, not a proven account of what causes ageing — a distinction its own critics have pressed hard [s3].

What the hallmarks are

The 2013 paper set out to identify common denominators of ageing across organisms, with an emphasis on mammals [s1]. It proposed nine "tentative" hallmarks: genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion and altered intercellular communication [s1]. The authors were explicit that a major challenge remained — untangling how the candidate hallmarks interconnect and how much each actually contributes — with the eventual goal of finding drug targets to improve health in later life [s1].

The 2023 update, "Hallmarks of aging: An expanding universe," raised the count to twelve by adding disabled macroautophagy, chronic inflammation and dysbiosis (disruption of the microbiome) to the original nine [s2]. It also proposed three criteria a process should meet to qualify as a hallmark: it should manifest with age; accentuating it experimentally should accelerate ageing; and intervening on it should be able to slow, stop or reverse ageing [s2]. That last criterion is the ambitious one, because it turns each hallmark into an implied drug target.

Why the framework caught on

The list did something the field genuinely needed. Ageing research is sprawling, and before 2013 there was no common vocabulary linking a telomere biologist to a microbiome researcher to someone studying protein misfolding. The hallmarks gave everyone a shared map, and its influence has been enormous — the 2013 paper is one of the most cited in modern biology.

It has also been useful in practice. As a checklist of the major foci of current research, it helps identify interventions — drugs, for instance — that plausibly touch several features of ageing at once [s3]. Much of the current longevity-drug pipeline is organised implicitly around it: senolytics target cellular senescence, the epigenetic-alterations hallmark underlies the epigenetic clocks used as biological-age readouts, and nutrient-sensing is the rationale behind interest in rapamycin and metformin.

The critique that matters

The most substantive objection is not that any hallmark is wrong, but that the list has been mistaken for an explanation. A 2021 critique in Ageing Research Reviews — pointedly titled "The hoverfly and the wasp," after a mimic that resembles something it is not — argued that the hallmarks of aging were modelled on the earlier and highly successful "hallmarks of cancer," but do not do the same job [s3]. The hallmarks of cancer, the authors argue, provide a genuine paradigm with real explanatory power: a causal account of how a normal cell becomes malignant. The hallmarks of aging, by contrast, function as a paradigm without being one — a descriptive checklist of things that go wrong, not a mechanistic theory of why they go wrong or which are causes rather than consequences [s3].

Their worry is that this resemblance is actively unhelpful. By looking like an explanation, the framework can obscure the field's continued lack of a real one, and the authors argue biogerontology needs to look beyond the hallmarks to understand the mechanistic causes of the diverse pathologies of ageing [s3]. This is a debate about scientific structure, not a fringe complaint, and the 2023 update partly answers it by proposing qualifying criteria and stressing that the hallmarks are deeply interconnected [s2] — though interconnection is itself part of the problem, because a network in which everything influences everything is hard to turn into a testable causal claim.

How to read a "targets a hallmark of aging" claim

For a reader, the framework is a lens, not a verdict. When a supplement, drug or clinic says it "targets a hallmark of aging," that phrasing borrows the authority of a well-cited scientific list without settling the two questions that matter: whether that hallmark is a cause of ageing or a symptom of it, and whether moving it in a dish or a mouse changes anything a person would notice.

The hallmarks are the best-organised summary the field has of what ageing looks like at the molecular level, and that is a real achievement [s1][s2]. They are not yet a theory of why we age, and the honest version of the science says so [s3]. Treat the list as a map of the territory still being explored — not as a set of levers already known to work.

Sources

1. [s1] The Hallmarks of Aging. Cell, 2013. https://doi.org/10.1016/j.cell.2013.05.039
2. [s2] Hallmarks of aging: An expanding universe. Cell, 2023. https://doi.org/10.1016/j.cell.2022.11.001
3. [s3] The hoverfly and the wasp: A critique of the hallmarks of aging as a paradigm. Ageing Research Reviews, 2021. https://doi.org/10.1016/j.arr.2021.101407