Weathered or unhealthy skin is emerging as a major risk factor for almost every single age-related disease, from Parkinson's to type 2 diabetes.

I'm canoeing through the Ardèche gorge in southern France – and attracting some peculiar looks. It's early afternoon on a blazing July day, and the sky is a perfect canvas of cobalt blue. Though the river is sheltered on either side by towering cliffs and limestone escarpments up to 300m (980ft) high, the sheer irradiating power of the sun has never been more visible to me. Its rays have turned the surface of the water into a winding path of scintillating light, so bright it blinds you to look at it. And I am taking no chances; I have chosen my outfit with the seriousness of an explorer trekking off into the Sahara.

The ensemble, my boyfriend remarks, is "extraordinary" – and he doesn't mean it as a compliment. My arms, hands and torso are completely covered with a long-sleeved top with built-in SPF protection – ordered over the internet from ozone-depleted-Australia, no less – while my head is shaded beneath a floppy fishing hat complete with its own fabric face shield. The final touches are several coatings of high-factor suncream, so my exposed skin has the pallid, sickly glow of titanium-white, and a pair of sunglasses. As my companion delights in telling me at 10-minute intervals, I am dressed like a large baby.

However, my vanity knows no bounds, and I am determined to avoid further sun-related ageing. But could there be other, hidden benefits to these extreme measures? In fact, is it possible that my obsession with maintaining healthy skin is a stroke of accidental genius? The answer to both these questions, it turns out, is yes.

The latest research suggests that our skin is not just a mirror for our lifestyles – reflecting the effects of years of smoking, drinking, sun and stress – and hinting at our inner health. No, in this new upside-down-world, the body's largest organ is an active participant in our physical wellbeing. This is a strange new reality where wrinkles, dry skin and sunspots cause ageing, instead of the other way around. 

A strange revelation

In 1958, the same year the US passed the law that led to the moon landings and the creation of Nasa, another major project was quietly conceived. The Baltimore Longitudinal Study was to be a scientific investigation of ageing with a daring and rather unorthodox premise.

Before then, it had been standard scientific practice to attempt to glean insights into the physiology of living people from donated cadavers – a practise with roots in the 19th Century tradition of graverobbing. But this time, subjects would be scrutinised somewhat earlier, while their hearts were still beating and their bodies were very much alive. The research followed thousands of adult men (and later, women) for decades, to see how their health developed – and how this was affected by their genes and the environment.

Just two decades in, scientists had already made some intriguing breakthroughs, from the discovery that less emotionally stable men were more likely to be diagnosed with heart disease to the revelation that our problem-solving abilities decline only slightly with age.

But one of the most striking findings confirmed what people had long suspected: how youthful you look is an impressively accurate expression of your inner health. By 1982, those men who had been assessed as looking particularly old for their age at the beginning of the study, 20 years earlier, were more likely to be dead.  This is backed up by more recent research, which found that, of patients who were judged to look at least 10 years older than they should, 99% had health problems.

It turns out skin health can be used to predict a number of seemingly unconnected factors, from your bone density to your risk of developing neurodegenerative diseases or dying from cardiovascular disease. However, as the evidence has begun to add up, the story has taken a surprise twist. Is the skin simply a living tally of the damage we have accumulated, or is it more complicated? Could it, in fact, be keeping healthy people healthy – and dragging unhealthy ones down further?

Another kind of birthday

There are two main ways to measure a person's age. The first is the standard method, known as chronological age – the kind tracked by revolutions of the sun. But there is also your biological age, which indicates the rate at which you are ageing physically – the maturity of your organs and cells. It can vary wildly between different people and even within the same body.

As we rack up the years, it's common wisdom that our chronological age will eventually catch up with our looks: skin becomes thinner and less even-toned, with lower elasticity, as the cells responsible for producing pigment and collagen die off or become "senescent" – meaning they stop renewing themselves and continue to exist in a kind of dormant state.

But it is the environment that tends to do the real damage. Though ultraviolet B (UVB) radiation can damage our DNA – leading to sunburn, mutations and skin cancer – 95% of the total UV radiation that makes it to the Earth's surface is ultraviolet A (UVA). This portion of the sun's rays has a longer wavelength, which allows it to penetrate deep into the dermis – where it breaks down collagen and stimulates cells to produce melanin.

At the microscopic level, photoaged skin – skin that has been aged by the sun – is thicker, with tangles of misshapen elastin and collagen fibres. At the visible level, it is often irregularly pigmented and significantly more wrinkled. This is true whether you have very light skin which is incapable of tanning, known as type one on the Fitzpatrick scale, or very dark skin, type six, which the scale inaccurately describes as never burning. Even deeply pigmented skin can burn and is susceptible to photoaging, though it will take longer for wrinkles to kick in. 

In fact, it's thought that intrinsic factors are responsible for the tiniest fraction of the classic "aged" look, while UV light is responsible for over 80% of visible skin changes. If you spent your whole life indoors with the curtains drawn, it's possible that you might not see significant alterations to this organ until you reach your 80s.

Crucially though, along with these effects the skin also undergoes a chemical transformation. And it is this that might be having a profound impact on our overall health.

A chemical cocktail

In 2000, at the birth of a new century, a radical new concept emerged. By observing the way most organisms respond to stress, a group of scientists at the University of Bologna, Italy suggested a new way to think about ageing.

In a young, healthy person, the immune system is routinely deployed to maintain order – patching up damage and shooing off infections. But as we get older, or when we are in poor health, these inflammatory responses can pass a certain critical threshold – a point beyond which they go into overdrive, releasing a cascade of potent chemicals that rampage around the body, destroying healthy cells and mutilating our DNA. Enter "inflammaging" – the simmering backdrop of inflammation that accompanies the ageing process.

This is where the skin comes in. The latest research suggests that wrinkly, diseased, or damaged skin becomes part of this system of inflammation, releasing a chemical cocktail that leads to yet further damage and inflammation. "Chronologically aged skin exhibits higher expression levels of a whole panel of inflammatory cytokines and chemokines," says Mao-Qiang Man, a research scientist at University of California San Francisco, who says that the same is also true for photoaged skin.

Locally, these chemicals degrade collagen and elastin, causing further skin thinning, wrinkles, and reduced elasticity, explains Tuba Musarrat Ansary, a postdoctoral researcher at Jichi Medical University, Japan. "They [also] disrupt the skin's barrier, increasing water loss and susceptibility to stressors," she says. The feedback loop is further compounded by senescent cells in the skin – either created by natural ageing or UV damage – which also release their own inflammatory chemicals.

But this is just the beginning. As the largest organ in the body, the skin can have a profound impact. The chemicals released by diseased and dysfunctional skin soon enter the bloodstream, where they wash around, damaging other tissues. Amid the ensuing systemic inflammation, chemicals from the skin can reach and harm organs that seem entirely unrelated, including your heart and brain. 

The result is accelerated ageing, and a higher risk of developing the majority of – or possibly even all – related disorders. So far, aged or diseased skin has been linked to the onset of cardiovascular disease, type 2 diabetes and cognitive impairment, as well as Alzheimer's and Parkinson's disease.

Though we're all familiar with the risks of smoking, drinking, overeating and a lack of exercise, you might argue that poor skin health is the elephant in the room – the one factor that we all routinely overlook. The good news is that there is a lot you can do to improve it.

A matter of moisture

The first step to protecting skin – and therefore, this new theory suggests, overall health – is to stay out of the sun. The most famous method is the "Slip, Slop, Slap," protocol, first launched in Australia in 1981. Today it has been expanded to include five central tenets: slip on a t-shirt [and ideally, other protective clothing], slop on high-factor suncream, slap on a wide-brimmed hat, slide on some sunglasses, and seek shade from the sun.

Plus, if the relationship between skin damage and age-related diseases isn't compelling enough to convince people to whip out their fishing hats and suncream, there are two very good reasons to try it. The first is that protecting your skin from the sun is extremely effective at preventing the visible signs of ageing.   

In one early study, those who wore a broad-spectrum SPF15 suncream every day for four and a half years did not show any signs of further skin ageing during this period. That's despite the fact that this low factor typically protects you from sunburn for just 15 times longer than it would take to happen without it –  so if your skin would usually start to redden in 10 minutes, you should be able to stay in the sun for just 150 minutes (two and a half hours).

Moreover, the suncream in the experiment did not specify the level of protection against UVA radiation, the kind that leads to skin ageing. In most parts of the world, to be classified as broad-spectrum, products must demonstrate that they not only absorb or reflect UVB radiation (indicated by the SPF rating), but also UVA. However, the degree to which they achieve this varies substantially. Dermatologists recommend that you always check the label for the UVA rating too, which is usually indicated by UV-PF or PPD.  

The second reason is that there is strong evidence suncream can prevent most of the inflammation that occurs when the skin is exposed to the sun – the first step towards developing age-related diseases.

But this is not the only way to keep your skin in good condition. In fact, by far the easiest way to improve the health of this organ is to moisturise. And there is direct evidence that this does reduce inflammation – and that it may help to prevent dementia.

Along with an uneven skin tone and wrinkles, both chronologically and photoaged skin is significantly drier. The humidity levels of human skin peak in the 40th year of life, after which they plummet, producing lower and lower quantities of its natural moisturisers – lipids, filaggrin, sebum and glycerol. This is a problem, because dehydrated skin is less effective as a barrier between the insides of our bodies and the outside world. When our skin is desiccated and flaky, its usual tasks – of keeping out infectious agents, environmental toxins, and allergens, while keeping in moisture – become significantly more challenging.

However, adding moisture back is not particularly complicated, whatever cosmetics adverts seem to suggest. And in the field of ageing, this simple intervention is showing remarkable results.

In one study, an international team of researchers – including Man – asked older volunteers to apply a topical moisturiser twice a day for one month. Compared to older participants who had not received any treatment, the subjects' skin was significantly restored, with lower levels of three different classes of inflammatory chemicals.

These promising results were quickly followed up with another study by the same team, which involved treating adults over 65 years old with a moisturising cream twice a day for three years. The participants' cognitive functioning was measured at the beginning and end of the study – and after three years, though the control group had declined significantly, those who had been hydrating their skin had not deteriorated.  

"Decreased stratum corneum hydration levels [those in the outer layer of the epidermis] are likely the major contributor to inflammaging," says Man, who explains that because dry skin tends to have higher levels of inflammation, it can feel itchy. And if you yield to the scratching impulse – you guessed it – the inflammation gets worse.

But, Man says, many natural ingredients can help. These include glycerol, petrolatum, hyaluronic acid and lipids that would usually be found in this layer of the skin – normal constituents of even the most basic moisturisers.

It's possible that simply drinking more water might also help to hydrate the skin, though the evidence is murky – some studies suggest there is not yet any support for this, while others claim it can help. It also hasn't been directly studied as a way to prevent inflammation or related diseases.  

To visualise the extent to which the skin is able to affect the rest of your body, it helps to think about just how much of it you have – then remember that, as you would expect, all the skin you can see on the outside of your body is matched by the exact same surface area on the inside. And when your skin is damaged, every inch is capable of releasing toxic chemicals.

So, protecting your skin from the sun really does pay off – but don't forget the moisturiser either. Please excuse me while I fetch my SPF50+, sunglasses, sun umbrella and most outrageously silly fishing hat… I have some gardening to do.

BBC

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