Vitamin A, sunscreen and stem cells

You’ve probably heard the word “metabolism” too many times – probably during every discussion about weight loss ever! *eye-roll*

What you probably didn’t realise is that your skin actually goes through a similar process called “epidural turnover”. Speeding up your skin’s metabolism is not just another buzz phrase to add to your wellness dictionary, but is in fact a way to protect your skin from external factors, thus reducing the signs of ageing.

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What is skin cell turnover and why is it important?

Firstly let’s review some skin anatomy and physiology! The skin is broadly structurally divided into two layers: the epidermis and dermis. The epidermis is the protective outer layer, containing skin cells (‘keratinocytes’) as the major cell population. Keratinocytes begin their life at the base of the epidermis and migrate upwards towards the surface, becoming flattened, losing their internal components, and developing a tough waterproof coat as they age.

The older keratinocytes we find at the epidermal surface are called ‘corneocytes’, and layers of these, embedded in lipids, comprise the ‘stratum corneum’, commonly known as our skin barrier. Corneocytes are eventually lost from the skin surface a by natural exfoliation process known as ‘desquamation’.

Meanwhile, our keratinocyte population is constantly renewed from specialised stem cells in the deep epidermis, ensuring this cycle is in constant motion.

Epidermal turnover is the complete keratinocyte-to-desquamated-corneocyte cycle, and it happens at a constant rate of around 40-56 days in healthy skin (your epidermal layer is renewed nearly a thousand times in your lifetime!). After age 50, this rate can slow dramatically, decreasing by up to 50%. Epidermal turnover is important for maintaining our skin’s barrier and appearance. A healthy skin barrier relies on the balance between production of keratinocytes and desquamation, and this process is regulated by a complex array of hormones, growth factors, and signalling chemicals.

Side note: So how do tattoos remain on the skin with all this turnover happening? The dermis does not turnover like the epidermis, so dyes implanted in the dermis stay put!

What happens to epidermal turnover as we age?

Aging involves two processes: intrinsic and extrinsic. Intrinsic aging is genetically programmed, and causes a slowing down of cellular processes as a result of accumulation of reactive oxygen species from cellular metabolism. Our skin cells respond by becoming less responsive to the normal stimulatory chemicals, and the epidermal turnover rate slows.

Older skin is therefore less able to repair itself after resurfacing procedures (like lasers, dermaplaning, dermabrasion, exfoliation), so it needs to be treated gently and by professionals. This is compounded by less efficient corneocyte desquamation from the skin surface, caused by changes to the type and amount of lipids produced in older skin. The dried out corneocytes then accumulate in the stratum corneum, giving skin a rough, dry, dull appearance.

But slowing the turnover cycle down isn’t the only issue – so is speeding it up!

Here we turn to the other form of aging – extrinsic ageing. This aging process is associated with external factors such as UV exposure, smoking, pollution, diet and lifestyle. For skin, the most important of these is UV exposure. UV has many effects on epidermal physiology, but from a turnover perspective, it causes changes to the regulation of the epidermal turnover cycle. This tricks the skin into overproducing keratinocytes to thicken the epidermis and protect itself from the sun. The resulting appearance is the rough, thickened skin we associate with chronic photodamage.

So what can we do to maximise epidermal turnover?

Of course it wouldn’t be a Dr Squire article without mentioning sunscreen! Prevention of UV damage is key to reducing signs of photodamage in skin (not just epidermal turnover dysregulation) – and is applicable for all age groups. Improve skin appearance by kick starting those keratinocytes! You can stimulate them to respond better to normal chemical signals, or provide some extra chemical signals. There are a few science-backed ways of doing this:

Vitamin A

Vitamin A (aka retinol) is a powerhouse for reducing fine lines. Amongst its myriad of other effects, italso powers up a sluggish epidermal turnover cycle to increase epidermal thickness and diminish fine lines.

Stem Cells

It’s impossible for topically applied stem cells to affect keratinocytes in skin. But there is evidence that you can power up your own native stem cells and repopulate keratinocytes that way. White blood cells produce a chemical called defensin in response to controlled skin wounding (by lasers, microneedling for example), which stimulates a stem cell called LGR6+ to produce keratinocytes. A 2018 study showed promising anti-wrinkle results with a topically applied skincare regime containing defensin.

Other chemical stimulators of Keratinocytes

New research has shed light on other topically applied chemicals that show promise in up regulating sluggish keratinocytes to improve skin quality. These include methylestradiol propanoate (MEP), a synthetic oestrogen for use in oestrogen-deprived skin, and heparan sulfate.

Dr Michele Squires’ prescription for boosting your skin’s metabolism

  • A good quality sunscreen: it must be broad spectrum, at least SPF30+
  • A Vitamin A: I only bother with prescription-strength for my 40+ clients. Over-the-counter retinols are fine for younger skin.
  • MEP – Emepelle skincare, which has just arrived in Australia, finally (I’m currently trialling this with a view to prescribing it for the right people).