You may have heard that skin repairs itself at night, but there’s a lot more to it than that.
The skin has its own ‘clock’, in fact it has many ‘clocks’ that regulate cellular functions throughout a 24 hour period. There’s an increasing amount of research published on the subject and shedding light on how intricately tied our skin’s functions really are to a circadian rhythm.
The timing of the skin’s circadian rhythm is triggered by light.
The eye retina registers light and sends a signal to a command centre in the brain (also called the suprachiasmatic nucleus SCN for any skin nerds) which is located in the Hypothalamus. This process sets the clock in motion and all of the skin functions that follow including, DNA repair, skin permeability and immunity.
So your skin has a bunch of internal gene clocks regulating its functions, what does that mean for you?
This means a few things.
For one, you want to make sure to take care of your "light hygiene". Obviously sleep is important, but if you can't fall asleep right away, at least turn off screens and turn down the lights. This will keep your sleep/wake cycle consistent, as well as your "skin clock". Expose yourself to natural light first thing in the morning and lower lights in the evening as you’re winding down for bed.
Day and night create widely different environments for the skin and the skin adapts accordingly through circadian rhythms.
During the day, skin needs to focus on protecting itself from pollution, bacteria, UV light, and varying temperatures. At night, we’re in a controlled environment (at home - most of us at least!). Your skin doesn’t need to focus as much on protection and puts more efforts into repair and regeneration.
How your skin protects itself during the day using circadian rhythms:
Sebum production: The skin produces more oil during the day. In fact, studies show that oil production peaks around noon and bottoms out around 4am. If excess oil is a problem for you, it’s best to focus on more water-based hydration during the day and use oil-based products during the night.
Sun protection: The cells responsible for the skin's pigment are called melanocytes. They function to help protect against sun damage. During the day, these cells synthesize and transfer UV absorbing melanin to their neighboring cells. This results in natural sun protection. In most cases though, our natural skin defense is not enough to protect us from sun damage and so regular sunscreen is necessary.
It’s important to know that when traveling to a different time zone, especially into a warm climate, your skin’s natural defense mechanism needs time to catch up. Your melanocytes may be a bit jet-lagged too and won’t immediately function on the same clock as your new destination! In this case, extra sun care and caution is needed to prevent bad burns.
Moisture: Skin is less permeable during the day. This means it can retain moisture better than at night. It’s speculated that skin needs more moisture during the day to withstand external environmental factors and defend against bacteria penetrating the skin barrier.
How your skin repairs itself at night using circadian rhythms.
Increased blood flow: Starting in the afternoon and evening, the rate of blood flow to the skin increases. This is most likely to assist in cellular repair. More blood flow brings nutrients and oxygen to the skin, which assist in repair. It also enhances product absorption. Studies have also shown that increased blood flow accelerates the rate of ingredients passing through the skin and making their way into tissues, particularly with medicated ingredients. The downside to this: anyone with inflammatory skin conditions like atopic dermatitis may notice more flare ups at night. Inflammation increases, along with skin permeability, resulting in drier, itchier skin.
Product penetration: The skin’s ability to absorb water-based and oil-based products peaks in the early morning hours, while it's still dark. Studies have shown that topical medicines (which are designed to have a higher absorbency rate than standard cosmetic products) had maximum penetration at 4:00AM and slowed during daylight. This is good news for any active ingredients you’re applying at night!
Moisture: Skin is more permeable at night, which is helpful for product penetration, but increases moisture loss. Trans Epidermal water loss is at its highest at night and into the early morning hours. This means you're going to want to apply more occlusive products over your regular serums and treatments. A water-less balm or oil, applied over your moisturizer, can help protect against moisture loss and keep skin plump and supple.
Cellular renewal: Keratinocytes, cells that make up the top layers of the skin, have a higher proliferation rate at night. In fact, cell division peaks at midnight and bottoms up around noon.
Knowing more about the way our skin functions means we can use products more strategically to get the results we want. Sleep aside, maintaining a consistent morning and nighttime routine by regulating our light exposure will help ensure our skin's circadian rhythms are functioning properly.