Skin is your largest organ
This oft-forgotten organ actually makes up 15 per cent of your bodyweight. The average human carries a Dachshund’s worth of skin: roughly 10kg covering two square metres.
Our outer organ is made up of two main layers. The outer ‘epidermis’ is as thin as a sheet of paper, yet it accounts for most of the skin’s barrier functions. The ‘dermis’ beneath is thicker and carries out a diverse range of roles: collagen and elastin give skin its shape, plumpness and elasticity, over 17 kilometres of blood vessels – enough to bridge the Strait of Gibraltar – and millions of sweat glands regulate body temperature by retaining or releasing heat, exquisitely sensitive nerve receptors enable us to feel our way through life and a standing army of immune cells waits for any foreign intruder. With its unrivalled diversity, skin is the Swiss Army knife of the organs.
Skin renews itself every month
Your paper-thin epidermis is scratched, squashed and stretched thousands of times a day, but it doesn’t break – at least not easily– or wear out. This is because the wall of the skin is constantly being supplied with new, living bricks: keratinocytes. These cells are made up of the tough protein keratin, which is unbelievably strong: it also forms our hair and nails, as well as the unbreakable claws and horns found in the animal kingdom. The word comes from the Ancient Greek for horn, keras, from which we also get rhinoceros.
Keratinocytes are constantly being formed from stem cells in the deepest layer of the epidermis, and slowly move up in layers throughout their month-long life until they form a formidable barrier, as waterproof as a raincoat, before flaking off into the atmosphere. When our outer wall is repeatedly beaten and battered, our epidermis responds by going into overdrive, and anyone whose epidermis suffers repeated rubbing is likely to have calluses, from builders to rowers.
Read more about skin:
- Getting under your skin: the surprising life of our largest organ
- A scientist’s guide to life: how to stay safe in the Sun
A midnight feast could lead to sunburn
Recent evidence suggests that our skin cells contain complex internal clocks that run on a 24-hour rhythm influenced by the body’s ‘master clock’ in the brain. Overnight, skin cells proliferate rapidly, preparing and protecting our outer barrier for the sunlight and scratches of the coming day. During the day, these cells then selectively switch on genes involved with protection against the Sun’s ultraviolet (UV) rays.
A 2017 study took this one step further and found, rather remarkably, that if we eat late at night, our skin’s clock assumes that it must be dinnertime and consequently pushes back the activation of the morning-UV-protection genes, leaving us more exposed the next day. So while studies are increasingly showing that a lack of sleep is detrimental to our overall physical and mental health, it now seems that our skin also benefits from additional sleep.
Eating colourful vegetables increases the skin’s perceived attractiveness
If you ever needed more motivation to eat your veg, science shows that it makes your skin more attractive. Carotenoids are red, orange and yellow pigments found in colourful fruit and vegetables, such as carrots, tomatoes and oranges. Evidence suggests that a diet rich in these foods gives skin an attractive glow, even if it is not clearly noticeable.
In a study in which women were asked to judge men’s faces – of any background skin colour – those with a yellow-red glow from colourful vegetables were deemed more attractive than those with either paler skin or a sun-tan. The golden-glow effect was an even more attractive magnet than the masculinity of the face.
Sunlight can be as addictive as drugs
That pleasurable feeling of basking in sunlight in the park or on the beach could well be an innate drive for us to acquire vitamin D. This vital vitamin lies inactive on the chopping board of our skin, waiting for the sun’s UV rays to dice it up into its active form. But sunlight is also the world’s most available carcinogen, and actively seeking it increases our risk of developing skin cancer. This is a particular problem for a large minority of us who are literally addicted to sunshine.
Sunlight exposure induces the skin’s synthesis of beta-endorphin, which enters the bloodstream and causes an opioid-like effect; opioids being the pain-relieving and addictive family to which morphine and heroin belong. In fact, 20 per cent of beachgoers show signs of Sun dependence that would satisfy the symptom criteria for addiction and substance abuse. ‘Tanorexia’, as it has been dubbed, is a real phenomenon.
Underarm bacterial transplants could cure body odour
Whether you like it or not, your skin is crawling with billions of microbes, including over 1,000 types of bacteria. Some members of this microscopic community – known as the skin microbiome – confer benefits to our skin, whereas others are downright devious and contribute to skin disease. New research is beginning to show that smearing the skin with probiotics containing ‘good’ bacteria can be used to treat common skin conditions including eczema and acne.
‘Bacterial transplants’ – relocating bacterial populations from the skin of one human to another – could even cure body odour. In a 2017 study, some of the underarm skin of one identical twin, who didn’t seem to smell at all, was scraped off and smeared into the smelly pits of the other twin who suffered from strong body odour. Remarkably, the smelly twin’s odour disappeared and the effects lasted for a year!
Tattoos are essentially fossilised immune cells
Why does ink drawn on our outer layer of skin disappear after a few hours but tattoos remain for life, and can even be detected on a 5,000-year-old mummy? Tattooing involves a needle impregnated with black ink penetrating beneath the outer epidermis and into the deeper dermis.
The needle fires into your skin at roughly a hundred times a second, intentionally causing many tiny wounds, alerting the body to damage. Immune cells in the skin, known as macrophages (‘big eaters’, from the Ancient Greek) rush to the damaged area, and engulf the ink particles, believing them to be foreign bacteria. But their eyes are bigger than their stomachs, and many of these macrophages end up stuck, with the pigment trapped inside them, locked in like intricate fossils on a cave wall.
If you sport a tattoo, spare a thought for the little fellows who went into battle thinking they were fighting an infection but were instead fated to spend the rest of their days embedded in your skin-based art.
Sweat is a love potion
The sweat factories in our dermis are capable of pumping out literally bucket loads of sweat each day, cooling the body down. But a specific type of sweat, produced by apocrine glands in the armpits and groin areas, also serves a very different purpose. The proteins, lipids and steroids in this sweat are broken down by skin bacteria to create body odour.
Although science has not isolated specific pheromones from our natural eau de parfum, humans are nevertheless exquisitely proficient at detecting their partner’s ‘odour print’. A prolonged sniff of your loved one will trigger happy memories and reduce stress levels. One study even found that, when sniffing sweaty t-shirts, women are more attracted to the sweat of men with dissimilar immune genes. Our skin-nose communication may be helping humans avoid incest and diversify their offspring’s immune systems.
Read more fascinating facts about our bodies:
- 5 strange things you did before you were even born
- 10 things you (probably) didn’t know about your mind
Blushing can smooth over a social faux pas
Many of us have erythrophobia – a fear of blushing – and none of us enjoy our skin signalling to the world that we are embarrassed. We feel as though others can see through our skin and into our mind. On the face of it, blushing doesn’t seem to serve any useful purpose, and Darwin was fascinated by it, calling it ‘the most peculiar and most human of all expressions’.
Although we sometimes want to disappear when we involuntarily go bright red, recent psychological research suggests that blushing actually serves a positive social purpose. When we blush, it signals to others that we recognize that a social norm has been broken; it is an apology for a faux pas. Maybe our brief loss of face benefits the long-term cohesion of the group. Interestingly, if someone blushes after making a social mistake, they are viewed in a more favourable light than those who don’t blush.
Millions today suffer in, or for, their skin.
Skin is an exquisitely social organ, and it sadly often shows humanity at its worst. People with albinism – who have a genetic absence of the skin’s dark pigment melanin – are subject to all forms of skin cancer from an early age, and without lifelong Sun protection as well as meticulous attention and treatment, their lives are cut tragically short. But for people with albinism in East Africa, they have much more to fear from their fellow man.
The greed of witch doctors and the poverty of the rural population have contributed to a belief that the body parts of albinos bring good fortune, wealth and political power. When a full set of albino body parts can fetch up to $100,000, it is easy to see why witch doctors are not short of recruits with murderous intent, and this cruel practice is sadly on the increase.
But the wonderful paradox of skin is that the more we discover about the science and beauty of our most human organ, the more we see that we really are no better or worse underneath.
The Remarkable Life of the Skin by Monty Lyman (£20, Penguin Books) is out now.