Our skin’s internal clock

The circadian rhythm is an endogenous time-keeping system that monitors a daily cycle of roughly 24 hours. It’s our body’s master pacemaker, regulating most of the physiological functions in our body, including hormone release.

What most people don’t know is that our skin is subject to a circadian rhythm as much as any other organ system. So, our skin cells have their own internal clock, but what kinds of changes are there in our skin throughout each 24-hour period?

We know for example that in the evening and at night our skin is more active in cell regeneration and repair than during the early day. One of the reasons for that is that the stem cells in the bottom layer of our epidermis (the ones that create new cells) are most active late at night (ie high proliferation rate).

That makes sense of course as at this time of the night, our skin cells are more likely to have the ‘peace’ to do so, without being constantly disturbed by the need for ‘fire-fighting’ (ie defending itself against environmental aggressors such as sun light and urban pollution).

It also makes sense, as proliferating cells are more susceptible to DNA damage (eg caused by sun light), so it would be more ‘dangerous’ to have their highest proliferation phase during the day from that perspective.

The most active time of the day for skin repair seems to be just before the mentioned proliferative peak at night, ie in the late afternoon and early evening, which again makes sense as it’s important to repair DNA damage first, before entering into a cell proliferative state.

I always recommend my patient to use anti-oxidant skincare (and SPF) in the morning (to fend of the environmental aggressors during the day), and a repair cream such as a vitamin A containing cream in the evening (to support the evening skin repair mode and the overnight cell proliferation and skin regeneration phase). This will also support the skin’s circadian rhythm nicely.

We also intuitively tend to apply slightly richer skincare in the evening (but please, please, please don’t overdo it!), as our skin’s barrier function is a little less effective at night, so it loses slightly more water (this increases skin ‘permeability’ at night also means on the other hand that active ingredients in skincare can be absorbed better at night, which is a silver lining – think repairing vitamin A derivatives!).

Sleep and skin

Good quality, restorative sleep is also crucial for the nightly cellular repair, regeneration and immune function. Every night, we go through repeated cycles of two distinctly different sleep phases: Rapid Eye Movement (REM, when the most active dreaming happens) and non-REM sleep (NREM, the deeper sleep). During NREM, blood flow is directed from our brain and body core, more towards the body’s periphery including the skin. Thus, a restorative hormone flow is established, and cellular repair is enhanced.

Sleep deprivation on the other hand is known to contribute to systemic inflammation, even after a short period of only a couple of weeks, as research has shown. In fact, sleep deprivation is thought to increase all sorts of age-related processes as well as chronic health problems.

At night we naturally release the ‘sleep hormone’ melatonin. Melatonin levels start to rise in the evening and peak around midnight before slowly subsiding again. This diurnal sleep-wake cycle is governed by the changes of light and darkness. If we don’t get enough sleep, our melatonin levels are impaired.

Interestingly, melatonin also helps protect our skin from the sun’s damaging effects and counteracts mitochondrial and DNA damage. Unfortunately, like so many other skin-friendly hormones, our melatonin level declines with age. Sleep dept will only hasten this natural decline.

Sleep deprivation is also known to impair insulin sensitivity and glucose tolerance and is connected to the development of diabetes. With regards to the skin, higher blood sugar levels mean higher generation of Advanced Glycation End products (AGEs), which again accelerate the skin’s ageing process.

Sleep is even connected to telomere length. Shorter telomeres have been associated with poorer sleep quality in women and shorter sleep in men. And in a fascinating genomic study, it was shown that sleep debt of only two nights led to a change in the expression of 500 genes. These changes were notably related to DNA damage and repair as well as stress and diverse immune system responses.

Sufficient sleep is also important for the nightly peak of our natural anti-aging hormone GH (growth hormone). This not only helps us look younger, but also helps to repair tissue. However, when we don’t get enough sleep, our natural GH level is sub-optimal – and this gets worse as we get older.

A study looking at the connection between sleep and longevity characterized the sleep patterns of people with a high life span (85 to 105 year olds) and compared these to other groups. The outcome confirmed the importance of maintaining strictly regular sleep-wake schedules.

Jet lag by the way temporarily messes up your internal body clock!

I am often asked whether there is any way of cheating the effects of sleep depth on our skin. The answer is that unfortunately it’s not possible to truly ‘compensate’ with skincare for lack of sleep. However, to use good skincare ingredients to stimulate collagen and elastin production certainly makes sense (although this should not be an excuse to continue not getting enough sleep!).

One of the most evidence-based skincare ingredients to boost collagen are vitamin A derivatives such as retinol and retinaldehyde. Even more effective is prescription strengths tretinoin. For people with very sensitive skin, peptides and/or growth factors can be a good alternative. As mentioneded, I would recommend using these repair ingredients in the evening and combine them with an antioxidant serum and SPF30-50 in the morning.