Senescence and Inflammaging

Two claims usually get bundled together in writing about senescence: that old cells drive the chronic inflammation of ageing, and that removing them will therefore make people healthier. The first is a well-described mechanism with a large supporting literature. The second is an untested hypothesis. Keeping them apart is the whole job.

The mechanism is well characterised

Cellular senescence is a cell-cycle arrest — in G1 or possibly G2 — that stops damaged cells from proliferating. In practice it is identified by three imperfect markers: senescence-associated β-galactosidase activity at pH 6, and expression of p16INK4a and p21. These cells accumulate at sites of age-related degenerative and preneoplastic pathology, and they are not inert. They release the senescence-associated secretory phenotype (SASP): cytokines, chemokines, growth factors and proteases, including IL-6, IL-8, TNF and matrix metalloproteinases.

Inflammaging is the parallel observation, named by Claudio Franceschi in 2000: most older people carry elevated blood inflammatory markers — IL-6, IL-1 and IL-1RN, CRP, TNF and soluble TNF receptors, IL-8, IL-18, interferons, TGFβ, serum amyloid A. Those markers are not idle. High-sensitivity CRP and IL-6 predict cardiovascular disease in middle-aged and older adults independent of other risk factors, and IL-6 predicts multimorbidity, frailty, disability and premature death.

Virus, infection, microscope — illustrating Senescence and Inflammaging

The outcome data are strong; the causal arrow is not settled. Reviewing the field in Nature Reviews Cardiology, Luigi Ferrucci and Elisa Fabbri wrote that whether inflammaging “contributes causally to CVD and other comorbid conditions or is instead a noncausal marker of some other underlying mechanisms is still debated.”

Three complications worth carrying

The markers are blunt. SA-β-gal “is not a sufficiently robust and specific marker of senescent cells” — apoptotic non-senescent cells stain positive too. Counting senescent cells in a living person remains genuinely difficult.
Senescence does useful work. The same programme contributes to embryonic patterning of the limbs, nervous system and gut endoderm, to wound healing, to resolution of fibrosis, and to tumour suppression. It is a double-edged process, not a defect.
Inflammaging may not be universal. A 2025 Nature Aging study measured 19 cytokines across four cohorts: InCHIANTI (Italy), the Singapore Longitudinal Ageing Study, the Tsimane of the Bolivian Amazon and the Orang Asli of Peninsular Malaysia. The industrialised cohorts showed the classic age-linked inflammatory axis. The two non-industrialised populations showed “markedly different axis structures with little to no association with age” and no association with age-related disease. The authors concluded inflammaging “appears to be largely a byproduct of industrialized lifestyles.”

Snail, clam, seashell — illustrating Senescence and Inflammaging

The intervention evidence is a different story

Question	Where the evidence stands
Do senescent cells accumulate with age and secrete inflammatory factors?	Well established across human and animal tissue
Can a drug measurably reduce senescent cells in people?	Yes, in a 9-person open-label study: adipose p16INK4a+ cells −35%, SA-β-gal+ cells −62%, with falls in circulating IL-6, IL-9, MMP-9 and MMP-12
Does clearing them improve a clinical outcome?	Not demonstrated. The one randomized controlled trial (60 postmenopausal women, 20 weeks) found no effect on its primary endpoint, P = 0.611
Does lowering inflammation improve non-cardiovascular ageing outcomes?	Not demonstrated. Anti-IL-1β therapy reduced recurrent cardiac events in >10,000 post-infarction patients, but “no definitive evidence exists that reducing inflammation can prevent or modify the progression of multimorbidity with frailty or sarcopenia”

That third row is the one the marketing skips. Target engagement — proving a drug hits the thing it is supposed to hit — is a real and necessary milestone. It is not evidence of benefit. Every over-the-counter product sold on senolytic mechanism is sitting on the first two rows of that table and implying the third.

Soil microbes, microscope, soil sample — illustrating Senescence and Inflammaging

The takeaway

Senescence and inflammaging form a coherent, well-documented mechanistic story, and inflammatory markers genuinely predict who does badly with age. What follows from that is much less clear: causality is contested, the marker set is imprecise, the pattern is weaker outside industrialised populations, and no controlled trial has yet shown that removing senescent cells changes a clinical outcome in humans. Understanding the mechanism is worth your attention. Acting on it is not yet supported. The state of the drug evidence is covered in more detail in our piece on senolytics.