How the sun sees you: The frenemy of our superhero skin

As the end of summer draws ever closer, Dr Nick Knight explores the skin's relationship with sunshine (if the summer weather returns before winter)

If you were going to design a set of superhero skills, you may consider a CV of talents that include protection from danger, super-senses, stretchiness, and regeneration abilities. Although it sounds like the stuff of fiction, you need actually look no further than your own skin. That’s right, your skin, the largest organ in your body, is full of these superhero skills.

Of course we also know that for every superhero, there is the ubiquitous part-time friend, part-time enemy (the modern day ‘frenemy’). For your skin, this frenemy is the sun, who with a surface temperature of 5,500 °C and mass 330,000 times that of Earth, is quite a force to be reckoned with. With increasing exposure to its ultraviolet rays, the creator of bad tan-lines and super-charged good moods, how does your skin really cope with sunshine?

Before exploring this, let us explore what your skin actually is. Your skin is not one but three distinct layers comprising the epidermis, dermis and subcutis. Each has distinct superhero roles, providing nutrition and structural support, while housing hair follicles, sebaceous glands, sweat glands, fat, blood vessels and nerves. Believe it or not, the dermis accounts for 15 per cent-20 per cent of your total body weight! Sadly, no, that does not make ‘excess skin’ a cause of the obesity epidemic.

With that clear, let me show you how your skin responds to sunshine. Firstly, as you warm-up, your brain’s thermoregulation centre triggers an action response to restore your body’s temperature homeostasis (‘balance’). Your skin helps this in three different ways. Firstly, to aid heat loss, tiny superficial arteriolar blood vessels in the skin widen by relaxing the smooth muscles of the blood vessels. This redirects your blood to miniscule skin capillaries and allows for increased heat loss by convection and conduction. That’s why your hands always look so ‘veiny’ in warm weather!

The second trick of your skin is the eccrine glands begin secreting sweat. This speeds up your sweat ducts with verve and gusto, through the sweat pores and onto the surface of your skin, allowing for heat loss via evaporative cooling. On the downside, if you are not drinking plenty of water and replacing lost salts, you can become dehydrated quickly. Finally for those of you, like myself, who have follicularly-endowed limbs, the hairs flatten to prevent heat-trapping in the layer of still air that would otherwise exist between the hairs. This also allows for increased air flow to your skin, thereby increasing heat loss by convection. We can thank tiny erector pili muscles for this since they relax, allowing the hair follicles attached to them to stay flat.

So your skin defeats the sun’s attempt at evil that time. However, as with any frenemy, the tide can turn, and the sun can decide to be a friend, working with our skin - this time to help make strong bones – bizarre as that may sound. It is thanks to a conveyer-belt of biochemical activity between your skin, liver, kidneys, and bowels. It is important to realise that you need vitamin D for making calcium - which promotes strong bones. So, when your skin is exposed, the sun’s ultraviolet light activates the pre-cursor to vitamin D, 7-dehydrocholesterol (the source of 90% of our vitamin D). This activated vitamin D pre-cursor then wanders off to your liver via the blood stream to be modified, before travelling to your kidneys where it becomes biologically ‘active’. Active vitamin D promotes calcium absorption for your gut and helps to maintain adequate levels in the blood to allow for normal bone mineralisation, bone growth, and bone remodelling (our skeleton regenerates approximately every three months).

Of course, in a world of superheroes, the friendliness of the sun may not last long before the enemy surfaces once again. Now, yes, in the short-term, safe levels of sun exposure allows for the tanning process and protects the skin by releasing more melanin from the skin’s melanocytes. However, excess short-term exposure to ultraviolet light directly damages the DNA in your skin causing sunburn. Since we all have different skin types, as identified by the Fitzpatrick Scale (a classification system for skin colour), this, along with our exposure rates, will largely dictate how badly we may burn.

Years of chronic over-exposure is even more dangerous, with the potential to cause a number of different skin cancers - now one of the most common cancer types globally. It is often a result of DNA damage by the sun’s ultraviolet rays to the outermost layer of the skin, the epidermis. These cancers divide into the more common but less serious non-melanoma cancers e.g. basal-cell carcinoma and squamous-cell carcinoma, and the more serious and potentially fatal malignant melanoma cancers.

So let us recap; your skin performs superhero feats to protect, climate control, produce and defend you and your body without hesitation. It exists, however, at the will of your decisions; you can decide to love and nurture your skin, to work in partnership to promote health, or you can decide to rebel like a stroppy teenager, let it burn, not protect it, and let it fail to serve you the way nature intended. Yes, get a nice tan but be safe and think about the long-term exposure risks. As always, I will end with my drier but critical doctor message: if you are concerned about anything on your skin, want advice about sun protection and risks of over-exposure, then visit your GP.

In the meantime, go ahead and give your skin a superhero cape.

Read more: How alcohol affects your liver and heart
Fast food and you: Too much fat, sugar, and salt

Dr Nick Knight is a junior doctor based in London with a PhD background in human performance. His blog on life as a doctor can be read at:

Or follow him via Twitter: @Dr_NickKnight

Life and Style
A monstrous idea? Body transplants might no longer be science fiction
Science An Italian neurosurgeon believes so - and it's not quite as implausible as it sounds, says Steve Connor
Demba Ba (right) celebrates after Besiktas win on penalties
footballThere was no happy return to the Ataturk Stadium, where the Reds famously won Champions League
Arts and Entertainment
Natural beauty: Aidan Turner stars in the new series of Poldark
arts + ents
Mia Freedman, editorial director of the Mamamia website, reads out a tweet she was sent.
arts + ents
Life and Style
ebookNow available in paperback
ebookPart of The Independent’s new eBook series The Great Composers
Arts and Entertainment
The write stuff: masters of story-telling James Joyce, left, and Thomas Hardy
arts + ents...begging to differ, John Walsh can't even begin to number the ways
Jose Mourinho on Sky Sports
footballEXCLUSIVE COLUMN Paul Scholes: It was not a leg-breaking tackle, as the Chelsea manager had claimed
Latest stories from i100
Have you tried new the Independent Digital Edition apps?

ES Rentals

    Independent Dating

    By clicking 'Search' you
    are agreeing to our
    Terms of Use.

    iJobs Job Widget
    iJobs General

    Recruitment Genius: Bookkeeper

    £23000 - £26000 per annum: Recruitment Genius: This small, friendly, proactive...

    Recruitment Genius: Photographic Event Crew

    £14500 - £22800 per annum: Recruitment Genius: This is a fantastic opportunity...

    Recruitment Genius: Software Developers - .NET / ASP.NET / WebAPI / JavaScript

    Negotiable: Recruitment Genius: A Software Developer is required to join a lea...

    Austen Lloyd: Corporate Tax Solicitor - City

    Excellent Salary: Austen Lloyd: A first rate opportunity to join a top ranking...

    Day In a Page

    HIV pill: Scientists hail discovery of 'game-changer' that cuts the risk of infection among gay men by 86%

    Scientists hail daily pill that protects against HIV infection

    Breakthrough in battle against global scourge – but will the NHS pay for it?
    How we must adjust our lifestyles to nature: Welcome to the 'Anthropocene', the human epoch

    Time to play God

    Welcome to the 'Anthropocene', the human epoch where we may need to redefine nature itself
    MacGyver returns, but with a difference: Handyman hero of classic 1980s TV series to be recast as a woman

    MacGyver returns, but with a difference

    Handyman hero of classic 1980s TV series to be recast as a woman
    Tunnel renaissance: Why cities are hiding roads down in the ground

    Tunnel renaissance

    Why cities are hiding roads underground
    'Backstreet Boys - Show 'Em What You're Made Of': An affectionate look at five middle-aged men

    Boys to men

    The Backstreet Boys might be middle-aged, married and have dodgy knees, but a heartfelt documentary reveals they’re not going gently into pop’s good night
    Crufts 2015: Should foreign dogs be allowed to compete?

    Crufts 2015

    Should foreign dogs be allowed to compete?
    10 best projectors

    How to make your home cinema more cinematic: 10 best projectors

    Want to recreate the big-screen experience in your sitting room? IndyBest sizes up gadgets to form your film-watching
    Manchester City 1 Barcelona 2 player ratings: Luis Suarez? Lionel Messi? Joe Hart? Who was the star man?

    Manchester City vs Barcelona player ratings

    Luis Suarez? Lionel Messi? Joe Hart? Who was the star man at the Etihad?
    Arsenal vs Monaco: Monaco - the making of Gunners' manager Arsene Wenger

    Monaco: the making of Wenger

    Jack Pitt-Brooke speaks to former players and learns the Frenchman’s man-management has always been one of his best skills
    Cricket World Cup 2015: Chris Gayle - the West Indies' enigma lives up to his reputation

    Chris Gayle: The West Indies' enigma

    Some said the game's eternal rebel was washed up. As ever, he proved he writes the scripts by producing a blistering World Cup innings
    In Ukraine a dark world of hybrid warfare and murky loyalties prevails

    In Ukraine a dark world of hybrid warfare

    This war in the shadows has been going on since the fall of Mr Yanukovych
    'Birdman' and 'Bullets Over Broadway': Homage or plagiarism?

    Homage or plagiarism?

    'Birdman' shares much DNA with Woody Allen's 'Bullets Over Broadway'
    Broadchurch ends as damp squib not even David Tennant can revive

    A damp squib not even David Tennant can revive

    Broadchurch, Series 2 finale, review
    A Koi carp breeding pond, wall-mounted iPads and a bathroom with a 'wellness' shower: inside the mansion of Germany's 'Bishop of Bling'

    Inside the mansion of Germany's 'Bishop of Bling'

    A Koi carp breeding pond, wall-mounted iPads and a bathroom with a 'wellness' shower