What they are

Twelve mechanisms, underneath everything

Twelve things go wrong inside a human body as it gets older. Not twelve diseases — twelve mechanisms, sitting underneath all the diseases. Scientists call them the hallmarks of ageing.

The word hallmark is doing real work there. A hallmark is not simply something that happens to you as the years pass. It is something that, if you push on it, changes how fast you age. Grey hair happens with age; push on grey hair and nothing else moves. Push on any of these twelve and ageing itself shifts.

Where the list came from

Five scientists wrote it down

Your body is a house nobody is allowed to demolish. Over time the wiring frays, the pipes fur up, the rubbish piles in the hall. Ageing is not one of those things going wrong. It is all of them, at once, slowly.

For almost all of history that was where the conversation ended. Ageing was simply what happened to people, and there was nothing to aim at.

Then in 2013 five scientists did something small and enormous. They wrote a list. Not of everything that changes as you get older — that list is endless and useless — but of the things that cause the changing. They found nine. Ten years later, twelve. It is what everybody in this field now aims at.

And what it means for you

You do not have to fix all twelve

This is the part most people miss, and it is the reason the list is good news rather than a longer list of things to worry about.

Vera Gorbunova
“many things go wrong with age, and you’re familiar with the hallmarks, and if you work to improve any of the processes affecting hallmarks, there will be benefit.”Vera Gorbunova · Biologist of long-lived animals, Rochester · ARDD, Copenhagen · 29 August 2024 · filmed on the quest

There is no entry exam. Any of the twelve you improve is progress, and most of the ordinary things — sleep, food, movement, the gap between meals — push on several at once without you ever knowing which.

It also turns advice into reasons. “Don’t eat all evening” stops being a rule somebody invented and becomes something you can picture: you are switching your cells’ recycling back on. That is the difference between a diet you abandon in March and a habit you keep.

Why only twelve

A thing has to be somewhere you can reach

Plenty of things happen to a body over the years. To get on this list, a thing has to get worse with age, speed ageing up when you make it worse on purpose, and slow ageing down when you ease it. Most things fail the last two.

Guido Kroemer
“a hallmark of aging should accompany the aging process and aggravate with time. That’s trivial. Wrinkles will do that, but they are not a point of your body that you can intervene on to improve aging. You just improve cosmetics.”Guido Kroemer · Cell biologist · Paris and Singapore · Singapore · 29 February 2024 · filmed on the quest

Twelve made the cut. Here they are.

The twelve

In the order the papers number them

Each one says what it is in ordinary words, what you can do about it, and how much that is — because for two of them the honest answer today is very little, and nobody else will tell you that.

The DNA collects typos.
The DNA collects typos.
01

Genomic instability

The DNA collects typos

Every one of your cells holds the same three-billion-letter instruction book, and has to copy it perfectly, again and again, while sunlight and its own chemistry attack the pages. The proofreaders are astonishingly good. Ageing is what it looks like when the typos start arriving faster than they can be caught.

What you can dolittle you can do today

Less than anyone selling you a pill will admit. What is beyond argument is what causes the damage in the first place: tobacco, sunburn, heavy drinking. After that the useful move is not repair but detection — the scans and blood tests that find the consequence while it is still small.

The science, in one sentence

Damage builds up in the DNA faster than the repair machinery can clear it, and some of it becomes permanent.

In the glossary
DNA repair
DNA repair

A maintenance crew working constantly on damage you never notice. Ageing is partly the crew getting slower than the damage.

What helps

Reduce the load rather than chase the repair: sun sensibly, do not smoke, keep alcohol modest, sleep. The single most useful thing here is not a supplement but screening — finding what went wrong early, which is the whole point of the Bridge of Prevention.

Oxidative stress
Oxidative stress

Rust, roughly. Some is normal and even necessary; too much damages what it touches.

What helps

The lesson of the last twenty years is that blanket antioxidant supplementation does not help and can blunt the benefits of exercise. Eat the colourful plants, train, sleep, avoid the obvious insults. Do not megadose vitamins to fix this.

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The lace ends fray.
The lace ends fray.
02

Telomere attrition

The lace ends fray

The ends of your chromosomes are capped, the way a shoelace is capped in plastic. Every time a cell divides the cap gets a little shorter. Run it down far enough and the cell stops dividing altogether — or becomes one of the troublemakers in number eight.

What you can dolittle you can do today

Very little you can buy, and the supplement shelf is a long way ahead of the evidence here. Nothing safely lengthens a human telomere. Smoking, carrying too much weight and years of unrelieved stress all shorten them faster, so the lever is your life rather than a capsule. And longer is not simply better: restarting the machine that lengthens telomeres is one of the tricks a cancer uses to make itself immortal.

The science, in one sentence

The protective caps on the ends of chromosomes shorten with every division; past a point the cell stops dividing or turns senescent.

In the glossary
Telomeres
Telomeres

The plastic tips on a shoelace. When they fray past a point, the cell retires.

What helps

Length is mostly inherited, and lengthening it on purpose is not something to chase — the same machinery is what cancers exploit. What is well supported: sleep, exercise, not smoking, and lower chronic stress track with slower shortening. Be sceptical of anything sold as a telomere lengthener.

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The instructions get misread.
The instructions get misread.
03

Epigenetic alterations

The instructions get misread

Every cell carries the identical book, and a set of bookmarks tells a liver cell to read the liver chapters and a skin cell to read the skin ones. With the years the bookmarks slide. Cells begin reading pages that were never meant for them, and doing the wrong job in the wrong place.

What you can dosomething you can do

This is where the frontier is loudest, because in animals the bookmarks have been pushed back where they belong. In people it is not a treatment yet, and anybody selling it today is selling ahead of the evidence. What is on the table now is dull and real: sleep, movement and not smoking all track with slower drift when it is measured.

The science, in one sentence

The chemical marks that decide which genes are switched on drift with age, so cells lose the identity of the tissue they belong to.

In the glossary
Epigenetics
Epigenetics

Switches on top of your genes. The sequence is fixed; which parts are switched on is not, and that is where lifestyle actually reaches your biology.

What helps

Epigenetic age tests have become widely available and remain noisy — useful as a trend over years, not as a single reading. Partial reprogramming, which resets these marks, is the most exciting thing in the field and is not yet a human therapy.

Partial epigenetic reprogramming
Partial epigenetic reprogramming

A conservator cleaning an old photograph. Go carefully and the picture comes back. Go too far and the picture comes off with the dirt.

What helps

Nothing you can do, and that is the entry. This is the frontier: it is in animals and in early company pipelines, and the risk it has to clear is cancer, because a cell that forgets what it is, is a tumour. It is on this page because it is the idea most likely to change what the rest of the page means — not because there is anything to take.

Biological age and the epigenetic clocks
Biological age and the epigenetic clocks

Two watches on a table. One counts birthdays and cannot be argued with. The other counts wear, and it can be running fast or slow.

What helps

The honest answer is that the clocks are better at measuring than at being moved. They respond to the things that already have hard outcome data behind them — exercise, sleep, not smoking, body composition — and a few small trials have shown a year or two of reversal. On consumer tests: the same sample sent twice can come back with different answers, so read one result as a rough position and a trend over years as the number that means something.

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Proteins stop folding properly.
Proteins stop folding properly.
04

Loss of proteostasis

Proteins stop folding properly

A protein is a long ribbon that only works once it is folded into one exact shape. Your cells fold millions a minute and throw away the ones that come out wrong. As the folding and the throwing away both get less reliable, the rejects stay where they are, and they clump together.

What you can doa lot you can do

Heat and hard effort both switch on the cell’s own folding crew — a sauna and a proper workout are doing the same job by different routes. And sleep earns more credit than it usually gets: a good deal of the clearing out happens overnight, particularly in the brain.

The science, in one sentence

The systems that fold proteins into shape, and dispose of the ones that fold wrongly, become less reliable, and the rejects clump.

In the glossary
Proteostasis
Proteostasis

Quality control for proteins. When it fails, misfolded proteins accumulate, and where they accumulate determines the disease.

What helps

Sleep, because clearance in the brain runs hardest then. Exercise. Enough protein, spread through the day rather than in one sitting. Heat exposure switches on the chaperone proteins that do this work.

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The clean-up crew slows down.
The clean-up crew slows down.
05

Disabled macroautophagy

The clean-up crew slows down

Cells eat their own broken parts and build new ones out of the pieces. It is the most efficient recycling scheme in nature, and it runs hardest when nothing is coming in. With age it slows, the rubbish stays where it falls, and a great deal of what ageing feels like from the inside is that pile.

What you can doa lot you can do

This is the one that answers to a decision you make at breakfast. Leave a real gap without food — a shorter eating window, or a longer fast now and then — and the crew goes to work. Hard exercise calls them out too. Coffee, green tea and olive oil each nudge it along. Rapamycin is the strongest trigger we know of, and it is a prescription drug still under study.

The science, in one sentence

The cell’s bulk recycling system, which breaks down its own damaged parts so the material can be reused, becomes less active with age.

In the glossary
Autophagy
Autophagy

Your body’s clean-up crew. It takes old, broken cell parts, breaks them down, and uses the pieces to build new ones. When it slows, the debris accumulates, and that accumulation is a big part of what ageing looks like from the inside.

What helps

Going without food for a stretch is the strongest everyday lever — time-restricted eating or a longer fast. Hard exercise does it too. Coffee, green tea and olive oil each nudge it. Rapamycin is the most convincing pharmacological route and remains a prescription drug under study.

Caloric restriction and fasting
Caloric restriction and fasting

Eating less, but not eating badly. The body shifts from processing a constant surplus to maintaining itself.

What helps

For most people, time-restricted eating and the occasional fasting-mimicking cycle capture most of the benefit without the cost. Sustained severe restriction carries real risks — muscle and bone loss especially — and is a poor trade after sixty.

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The fuel gauge stops reading true.
The fuel gauge stops reading true.
06

Deregulated nutrient-sensing

The fuel gauge stops reading true

Your body is always asking one question: is there food about? Insulin, mTOR, AMPK and the sirtuins are how it answers. Answer “plenty” every hour of every day and it never switches out of building mode into maintenance mode. Growth and repair are opposites, and ageing is partly the gauge jammed on full.

What you can doa lot you can do

The most answerable thing on this whole page. Eat inside a shorter window. Keep the refined carbohydrate down. Stay strong and stay lean. Walk after a meal — ten minutes moves this more than most supplements do. Metformin has convincing mouse data and has not yet shown the same in healthy people.

The science, in one sentence

The network that reads how much food is available — insulin, mTOR, AMPK, the sirtuins — stops reporting accurately, so cells keep building when they should be clearing.

In the glossary
mTOR and its suppression
mTOR and its suppression

A manager that decides whether the cell builds or cleans. Left on permanently you get growth without maintenance. The goal is not to switch it off — you need it to build muscle — but to stop it running all day.

What helps

Periods without food and without constant protein. This one has a real tension in it: the same signal that drives ageing also builds the muscle that keeps you alive after seventy. Most people over fifty need more protein, not less, and the cycling matters more than the average.

AMPK
AMPK

A fuel gauge that, when it reads low, tells the cell to tidy up and burn what it has rather than store more.

What helps

Exercise is the most reliable activator anyone has found. Metformin and berberine act here too; metformin’s longevity effect in healthy people is still being tested, and the large TAME trial that would settle it has not yet reported.

Insulin sensitivity
Insulin sensitivity

How well your body handles what you eat. When it slips, blood sugar stays high for longer after every meal, and the damage is cumulative.

What helps

Muscle is the largest glucose sink you own, so resistance training matters as much as diet. Walking after meals works. A continuous glucose monitor worn for a few weeks is one of the few pieces of consumer tech that reliably changes behaviour, because you see your own response rather than a general rule.

Sirtuins
Sirtuins

A repair crew that only clocks in if there is enough of a particular fuel around. Much of the last decade of longevity supplements has been an attempt to top up that fuel.

What helps

This is where the story has changed most since 2023. NAD+ precursors reliably raise NAD+ in blood; what they have not yet shown is that this makes healthy people live longer or better. Treat the supplement claims with more caution than the 2023 version of this page did. Exercise and sleep remain the unglamorous route.

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The power stations falter.
The power stations falter.
07

Mitochondrial dysfunction

The power stations falter

Mitochondria are the small engines that turn food and oxygen into the energy every other process on this page runs on. With age there are fewer of them, they leak, and the broken ones are cleared away more slowly. Tiredness that sleep does not fix is often this. So is a good deal of what people mean when they say they feel old.

What you can doa lot you can do

Exercise, and it is not close. It is the only intervention known to build new mitochondria in a living human being: endurance work grows them, interval work does it fastest. Nothing on any shelf comes near it, whatever the label promises.

The science, in one sentence

Mitochondria become fewer, leakier and less efficient, and the damaged ones are cleared away more slowly.

In the glossary
Mitochondria
Mitochondria

Your power plants. More of them, working better, is most of what people mean when they say they feel energetic. It is one of the most trainable things about you.

What helps

Zone 2 endurance work builds new ones; high-intensity intervals improve the ones you have. Doing both beats doing either. Supplement evidence here is modest next to the training effect.

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Old cells refuse to leave.
Old cells refuse to leave.
08

Cellular senescence

Old cells refuse to leave

A damaged cell has two honourable options: repair itself, or die. A third kind does neither. It stops dividing, refuses to leave, and spends the rest of your life shouting inflammatory signals at the healthy cells around it. A few are useful — that is one way the body stops a damaged cell becoming a tumour. Too many, and the whole tissue ages around them.

What you can dosomething you can do

Exercise clears some of them, which is one more reason it turns up on nearly every entry here. Senolytics — drugs that persuade these cells to finally die — are the most watched idea in the field, and they are in human trials, not on a shelf. Anything sold to you today as a senolytic supplement is running ahead of what has actually been shown.

The science, in one sentence

Damaged cells stop dividing but do not die, and broadcast an inflammatory signal into the tissue around them.

In the glossary
Cellular senescence
Cellular senescence

Cells that retired but stayed in the building, complaining loudly enough to make everyone else worse at their jobs.

What helps

Clearing them extends healthy life in mice, which is why senolytics attracted so much attention. Human trials so far have been small and the results mixed. This is a genuinely promising area that is not yet a thing you should be dosing yourself for.

Hormesis
Hormesis

Give the body a small challenge and it over-repairs. That is why training, heat, cold and fasting all work by the same logic — you are not avoiding stress, you are choosing the right size of it.

What helps

Exercise, sauna, cold exposure, fasting. Sauna has the strongest population data behind it. Cold has become fashionable well ahead of its evidence — it feels excellent and the long-term claims are thinner than the enthusiasm suggests.

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The repair pool runs low.
The repair pool runs low.
09

Stem cell exhaustion

The repair pool runs low

Every tissue keeps a reserve of unspecialised cells — apprentices, waiting to replace the workers who wear out. The reserve shrinks over the years, and the ones left answer the call more slowly. It is why a cut closes in three days at sixteen and takes a fortnight at sixty.

What you can dosomething you can do

Nothing you can buy, and clinics offering stem cell injections for ageing are selling well ahead of the evidence. What protects the reserve is unglamorous and free: sleep, enough protein, lifting something heavy twice a week, and not smoking.

The science, in one sentence

The reserve of cells that replaces worn-out tissue shrinks and answers more slowly, so healing slows and tissues thin.

In the glossary
Stem cell exhaustion
Stem cell exhaustion

A workshop keeps a rack of good blank timber for repairs. Every year the rack holds a little less, and what is left is harder to work. Nothing looks wrong until something needs mending.

What helps

Nothing yet reliably rebuilds a reserve in a human. Protecting it is well established: resistance training keeps the satellite cells in muscle active, sleep and control of chronic inflammation reduce the drain. Stem cell transplants are standard care in a few blood cancers and are not an anti-ageing treatment — clinics selling infusions for ageing are selling ahead of the evidence, and some of what they sell is dangerous.

Sarcopenia
Sarcopenia

Muscle quietly leaving. It starts in your thirties, and almost nobody notices until it costs them something — a fall, a stair, an independence.

What helps

This is the one on this list with the least ambiguity and the most leverage. Resistance training at least twice a week, enough protein, and vitamin D if you are low. Grip strength and how fast you can stand up from a chair predict how the rest of your life goes better than most blood tests.

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Cells stop talking properly.
Cells stop talking properly.
10

Altered intercellular communication

Cells stop talking properly

A body is an organisation of forty trillion members, and it only works because they keep each other informed — by hormone, by immune signal, by nerve. With age the messages get noisier and the departments stop hearing one another. Each starts optimising for itself, which is exactly how an organisation fails.

What you can dosomething you can do

This is where Kroemer’s point does the work: everything is connected, so improving any other entry on this page improves this one too. Directly, the levers are sleep, daylight early in the day, and keeping the background burn of number eleven down.

The science, in one sentence

The signalling between cells and between organs — hormonal, immune, neuronal — becomes noisier and less coordinated.

In the glossary
Klotho
Klotho

A thread being spun. How much of it there is seems to set how long, and how evenly, the spinning goes on.

What helps

Exercise raises it modestly, and so does looking after your kidneys, which is where most of it is made. There is nothing to buy: klotho does not survive being swallowed, and injected forms are in early trials. What it is genuinely useful for today is as a marker — something to measure rather than something to move.

Stress, cortisol and the alarm that never switches off
Stress, cortisol and the alarm that never switches off

An alarm built to ring for a minute, ringing all night. The sound is not the problem. Not being able to switch it off is.

What helps

Sleep is both a cause and a cure, and it is the first thing to fix. Exercise raises cortisol briefly and lowers the baseline. Breathwork and meditation have real if modest effects on the hormone and larger ones on how the stress is experienced. Connection matters more than most people expect — loneliness is a chronic stressor with its own mortality signal. And the most useful move is rarely a technique: it is removing one of the things that is ringing.

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A fire that never goes out.
A fire that never goes out.
11

Chronic inflammation

A fire that never goes out

Inflammation is how a body fights and repairs, and it is meant to flare and then stop. This one never stops: a low, body-wide burn that rises with the years even when there is nothing to fight. It is quiet enough that you cannot feel it and loud enough to damage tissue for decades.

What you can doa lot you can do

Sleep, weight, muscle, oily fish — and the two nobody mentions: look after your gums, and treat a quiet infection rather than living alongside it. This is also the one entry here you can actually watch. An ordinary blood test shows it, which makes it the rare case where you can see whether what you changed worked.

The science, in one sentence

A low, persistent, body-wide inflammatory state that rises with age even without an infection to fight.

In the glossary
Chronic inflammation
Chronic inflammation

A fire that never quite goes out. You do not feel it day to day, which is exactly why it does so much damage over decades.

What helps

Sleep, weight, muscle, oral health, and treating the obvious sources. Omega-3s have decent evidence. This is also one of the few processes where a simple blood test — high-sensitivity CRP — tells you something useful and cheap.

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The gut garden loses variety.
The gut garden loses variety.
12

Dysbiosis

The gut garden loses variety

A couple of pounds of microbes live in your gut, and they are not passengers. They train your immune system and manufacture compounds your own cells cannot make. A young gut is a garden with forty species in it. An older one is often six, and the weeds are winning — while the wall between the garden and the bloodstream grows leakier.

What you can doa lot you can do

Variety beats any single superfood: thirty different plants across a week does more than any powder. Fibre feeds the good ones, fermented food adds to them. Take antibiotics when you genuinely need them and not when you do not. Probiotic capsules are sold a long way ahead of what the trials actually show.

The science, in one sentence

The gut’s microbial community loses diversity and shifts toward species that provoke inflammation, while the gut wall grows more permeable.

In the glossary
The gut microbiome
The gut microbiome

A garden you did not plant and cannot see, which feeds you back. While it is varied it looks after the wall between your gut and your blood. When it thins, that wall leaks a little, and the immune system spends its life mildly annoyed.

What helps

Plant variety is the strongest and dullest answer — the number of different plants in a week beats any supplement in the data there is. Fermented foods raised diversity and lowered inflammatory markers in a controlled Stanford trial. Fibre feeds what is already there. Probiotic capsules are far weaker than their marketing; most strains pass straight through. Antibiotics cost diversity for months, which is a reason to need them rather than to want them.

Back to all twelve

Six more of the people we filmed

On the same twelve

Not everybody sees this list the same way, and the last one here does not much like it at all. Tap a face.

“If you look at these hallmarks of aging, we’ve got multiple ideas to tackle every single one of them, and it would just be wildly unlucky if in the next few decades, literally none of those things work.”Andrew Steele · Author of Ageless · Longevity Summit Dublin · 16 August 2023 · filmed on the quest
“we call those the hallmarks of aging. It’s a really convenient way to organize the field. They, by the way, they are linked to each other.”Eric Verdin · President and CEO, the Buck Institute · Novato, California · 22 May 2024 · filmed on the quest
“Used to be nine. 12 hallmarks of aging, so 12 things that we think are the drivers of the underlying causes of aging. But they’re kind of confusing and very scientific, and I feel like pretty unapproachable for just the general public.”Amy Killen · Longevity and regenerative physician · Salt Lake City · 29 May 2024 · filmed on the quest
“are you going to age more through inflammation? Are you going to develop more cellular senescence in your body? Are you gonna have cell-cell communication issues? So the hallmarks of aging. The well-known twelve hallmarks of aging, that we can capture using the machine. Maybe I will age in a different way, right?”David Furman · Director, Stanford 1000 Immunomes Project · Boston · November 2024 · filmed on the quest
“the TOR protein that it inhibits makes a lot of sense ’cause it’s right at the center of all of these hallmarks of aging.”Brian Kennedy · Professor of biochemistry and physiology, NUS · Singapore · October 2023 · filmed on the quest
“if you say like mitochondrial hallmark, that concept is a little bit limiting because what transition is the whole system that transitions, and we need to develop ways to describe a whole system.”Vadim Gladyshev · Professor of medicine, Harvard · Boston · 4 November 2024 · filmed on the quest

Where these came from

Three papers

2013

The original nine

López-Otín, Blasco, Partridge, Serrano & Kroemer, The Hallmarks of Aging, Cell 153, 1194–1217.

2023

The twelve

The same five authors, Hallmarks of aging: an expanding universe, Cell 186, 243–278.

2024

A proposed thirteenth

Faria, Ganz, Galkin, Zhavoronkov & Snyder, Psychogenic aging, Translational Psychiatry 14, 226.

The list is not finished. The candidate closest to being taken seriously is the mind itself — the argument that stress, loneliness and outlook act on the same machinery as everything above. It is a proposal, not a hallmark. It has not been adopted into the twelve, and this page will say so until it is.