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Dr Tiina Meder July 25, 2024

Circadian Rhythms: Why Does Our Body Need a Clock?

All creatures, great and small, follow the Earth's rhythms. The light and dark of day, moon cycles and ocean tides, seasonal changes and full 365-day yearly cycles. No one can be free from this pattern. Plants and animals, sea life and human beings are all involved in this cosmic rhythmic dance and light cycle.

A 24-hour day and night cycle is called a circadian where Latin circa stands for about and dias for day. Our body clock follows this cycle naturally.

Most people feel sleepy at night and refreshed in the morning with no special effort with the help of the body's internal clock. Circadian biology, circadian system, circadian medicine and circadian skincare are becoming a part of our lives, but circadian science is still very young.

The term circadian rhythms was invented by Franz Halberg in 1957. It defined the 24-hour cycle, but a real scientific breakthrough happened much later.

The 2017 Nobel Prize in Biology and Medicine for the discovery of molecular mechanisms and body processes controlling circadian rhythms acknowledged many years of scientific research by Jeffry C. Hall, Michael Rosbash, and Michael W. Young. Nowadays, circadian biology is a prominent and progressive area of biological science.

How Does Circadian Rhythm Work?

Our body has a special structure located in the brain, called a master clock or primary clock which orchestrates rhythms in all organs and tissues to help the body function properly.

It is a small structure with a big name of suprachiasmatic nucleus located in the hypothalamus and linked directly to the eye retina via optic nerve. When bright light affects retina, it not only sends an image to the brain cortex but also signals to the brain master clock, adjusting our body to reality.

That's why you probably feel more energetic on sunny mornings and sleepy on grey winter days — the power and intensity of light make the internal clock work slightly differently. The human circadian clock ensures that biochemical, physiological and biological processes occur at the optimal time of day, which is especially important for the skin.

Skin is exposed to light as well as to all other environmental factors, and all physiological processes in the skin are distinctively different for the duration of the light-dark cycle. Some processes in the skin can happen only once a day in a specific time or phase of the sleep-wake cycle, and if circadian rhythms are troubled, the skin damage could be significant.

What is interesting is that retinol enzymes play a major role in the functioning of the circadian rhythm and peripheral skin clocks. The thing to keep in mind is that, potentially, the circadian rhythm of your skin could be disrupted by overuse of retinol-based skin care as well as by vitamin A deficiency.

Recent scientific findings suggest that the suprachiasmatic nucleus, aka master clock, is not the only biological clock in the body. In fact, each organ and tissue have structures acting as clocks for the circadian system, synchronizing a specific function with other organs and master clocks.

In the skin, circadian rhythm clocks are located in different types of skin cells but mostly in the keratinocytes, cells of the superficial skin layer called epidermis. Pigment cells, melanocytes, immune cells, and cells of the deeper skin layer called the dermis also show circadian rhythm clock activity.

The biological clock in organs and tissues is the structure called the peripheral clock or peripheral oscillator as opposed to central clocks in the brain. But don't imagine miniature clocks with small arrows!

The biological clock comprises specific proteins with regulated expression patterns of the human body throughout the day. With tight regulation of time-sensitive clock genes, signals generated by the central circadian rhythm clocks are amplified at the skin to manage and control all skin functions.

What Can Adjust the Circadian Rhythm and Biological Clock?

Circadian rhythm reacts to many stimuli, also called zeitgebers. The primary zeitgeber is light — visible, ultraviolet, infrared and blue are contributing to stimulation. Blue light is known as a primary factor activating morning activity in the body and all other organs.

Naturally, morning light has more of a portion of blue light. By enhancing circadian zeitgebers, it activates alertness, hormone production, and skin's protective functions. It is beneficial, and a lack of blue light in the morning can lead to a disrupted circadian rhythm.

However, over-exposure to blue light in the evening can lead to disruption of how circadian rhythms work, reactivating day functioning of skin cells and suppressing night's repair in the skin.

Night blue light exposure is a modern-day problem created by the massive use of electronic devices that emit blue light, which affects our eye's retina. Blue light emitted by devices doesn't harm skin directly, but disrupted circadian rhythms triggered by regular exposure to blue light could lead to accelerated skin aging and even to the manifestation of skin conditions and diseases.

Light signals are called photic, and they are most important for circadian rhythm regulation. Non-photic signals or zeitgebers include sounds, feeding and fasting, temperature changes and behavioral factors.

Circadian Rhythm Sleep Disorders

You might have never heard of them, but circadian rhythm disorders, as well as other sleep disorders, are a problem for a wide range of people all around the world. Mostly, this is an issue for the ones with irregular sleep schedules, like shift workers and people who travel through time zones a lot.

Based on the causes and sleep-wake cycle changes it induces, other names include advanced sleep phase disorder, shift work disorder, delayed sleep phase syndrome, and jet lag disorder. The symptoms that might require a visit to a sleep specialist include:

Core body temperature changes;
Severe jet lag symptoms that last for days;
Daytime sleepiness;
Irregular sleep-wake rhythm;
Bright light sensitivity;
Not getting enough sleep on a regular basis.

The specialist will gather all the necessary data about your lifestyle as well as your sleep schedule. After that, he will choose a combination of solutions that help induce sleep and regulate your circadian rhythms.

These usually include melatonin supplements and light therapy. Hormone melatonin induces sleepiness, and for people without any circadian rhythm disorder, its production starts after the dark. Since circadian rhythm has a direct connection to our perception of light and dark, melatonin production suffers a lot from the rhythm disorder.

Which Skin Functions Are Regulated by Biological Clocks and Circadian Rhythms?

The simple answer is short — all of them! Regulated circadian rhythm activities allow the skin to adapt its daily functions to the constantly changing environment. External stimuli like temperature, light, humidity, UV radiation, and pathogens interact with the skin in a predictable time, and the skin adjusts functions to better respond to each challenge.

There is the best time for skin cell proliferation, higher and lower skin hydration and transepidermal water loss (TEWL), capillary blood flow, sebum production, change of temperature or pH, and even the appearance of wrinkles (yes, wrinkles appear deeper after lunch!)

We know the precise time when cells are actively dividing — it happens around 11.30pm and that's why the necessity of so-called beauty sleep, i.e. going to bed before midnight to look your best, is not really a myth, but truth. Cell growth and repair occur mainly in the evening, and skin is more vulnerable to damage at this time.

Sebum glands are more active during the day with a pic of their activity between noon and 4pm when they produce sebum most intensely. It helps to get fresh, non-oxidized lipids to cover the facial skin with a protective mantle right on time of higher ultraviolet activity.

In the early evening, sebum production decreases and comes to a full stop at midnight, staying minimal until 4am, which explains why skin is less moisturized in the early morning. Recently, it was found that the skin's microbiome follows circadian rhythms as well, with a higher activity of bacteria that is able to hydrolyze lipids and produce antioxidants.

One of the key players here is Cutibacterium acnes, which is beneficial but could become a problem when it overgrows. Circadian rhythm disorders can trigger or worsen acne conditions when sebum production doesn't stop or bacteria continue to grow during the night instead of following a healthy circadian rhythm regulation.

Skin hydration depends on many factors, including skin permeability and the amount of water lost across the epidermis. Transepidermal water loss (TEWL) is significantly higher at night when the skin is focused on the regeneration process and is supposed to be protected from external cues like ultraviolet and other environmental damage.

The permeability of skin is higher during the night too, so all skincare products applied on the skin at the evening time are penetrating deeper and could be acting more intensely. It is a myth that you need more intense skincare as a part of your bedtime routine, but you definitely need different skincare as skin functions are different, and we should respect that.

The skin's immune system also follows circadian rhythms, staying in protection mode during the day and in repair mode during the night. Apparently, skin sensitivity is linked to circadian regulation as well.

People with sensitive skin, as well as patients suffering from eczema, atopic dermatitis, and other skin conditions, are experiencing more itching and discomfort during the night because of excessive immune cell's night activity. Good sleep and healthy biological clocks are key to skin health!

Day Skin Life — Vigilance Mode.

Skin barrier building
Highest sebum production
Highest pH
Highest skin thickness
Lowest cells proliferation
Highest activity of microbiome
Lower blood circulation flow

Night Skin Life — Repair Mode.

Highest DNA repair
Highest cell proliferation
Highest blood circulation flow
Highest skin temperature
Highest skin permeability
Highest skincare penetration
Highest moisture loss
Lowest barrier recovery rate

How Do Eating Habits Affect the Skin’s Circadian Rhythm?

Food is the next important factor that controls circadian rhythms regulation of the skin after light. Food intake immediately changes the expression of more than 2000 genes in the skin.

Our skin is adapted to day feeding, and if you eat during daylight time, it helps your skin adjust better to the circadian rhythm. Night feeding could be disruptive and slow down skin night repair.

The same effect shows a high-fat diet, which can lessen skin's protective functions and increase ultraviolet skin damage. Calorie restrictions are seen as beneficial intervention helping to restore healthy circadian rhythms in the skin.

If you want to keep your skin's circadian regulation healthy, avoid eating in the late evening and during the night. Be careful about a high-fat diet, especially after lunch, and try to keep your energy balance under control.

7 Useful Tips to Help Your Skin’s Circadian Rhythm

Keep a consistent sleep schedule. Try to go to bed and wake up at the same time, and do not change it too much during holidays or weekends. If you feel constantly tired waking up early, maybe you are a biological night owl! We all are different, and it is a good idea to find your circadian rhythm individuality. The best time to do it is on holiday when you can try to go to bed and wake up naturally and see what sleep cycle makes you feel more energetic, and your skin looks better. Healthier to adapt your professional activity to your biological clocks than try to adapt your clocks to your job.
Avoid using electronic devices for at least 2 or 3 hours before you fall asleep. It helps to keep circadian rhythm regulation healthy as the blue light emitted by devices reactivates "morning functions" in the skin. If you cannot avoid it, try to use blue light filters to prevent circadian rhythm disorder.
Avoid eating for at least 2-3 hours before you fall asleep. Night eating, especially high-fat food, can disrupt circadian rhythm regulation, lead to irregular sleep-wake rhythm, and provoke accelerated skin aging.
Protect your skin during the day to prevent circadian rhythm disorders. Your skin is already focusing on protection, and it is better not to controversy it. Avoid using skincare that disrupts a natural barrier function or photo-sensitizing skin care, such as retinol or acid-based products, essential oils, or any other potentially irritating ingredients. Use a gentle cleanser and antioxidant skincare during the day, followed by sunscreen.
In case of skin dryness, use more moisturizing skin care products during the night. Hyaluronic acid, aloe vera juice extract, carrageenan, glycerin, and other water-holding ingredients help to keep skin hydrated during the night sleep cycles and create a healthy basis for day protection.
In case of skin oiliness, focus on day sebum regulation and protection. Apply sebum-regulating skincare in the morning and use oil-free sunscreens. If your skin is oily and acne-prone, it could be beneficial to cleanse up your skin after lunch and re-apply sebum-regulating skincare and sunscreen if needed. Use sebum-regulating skincare at night only in case of severe oiliness or acne.
Create your night skincare routine based on your individual skin needs. It should help your skin to repair efficiently and prepare for the next day's activity. Cleanse up your skin gently but properly, and use a moisturizing and naturally stimulating skincare. The best choice is skincare based on peptides and plant stem cell extracts, enriched with prebiotics and probiotics, helping to restore healthy skin's microbiome. If your skin is sensitive, use calming skincare products to reduce inflammation and discomfort.

How Age Affects Circadian Rhythms in the Skin

The causes of skin aging are largely classified as intrinsic and extrinsic. Intrinsic aging is strongly correlated with biological age and is explained by cumulation of DNA mutations, increased oxidative damage, alteration in hormonal level, and stem cell dysfunction.

Extrinsic aging mechanisms involve environmental factors such as ultraviolet damage, air pollution, and smoking. Circadian rhythm disorder contributes mostly to intrinsic aging as mutations in the clock genes are cumulating progressively with age.

Aging literally re-wires rhythmic genes in the skin as well as in the body. Skin response to zeitgebers is delayed, autophagy is decreased, and oxidative stress becomes more influential as more free radicals are generated and cumulated in skin cells.

It leads to disruption of the skin's barrier function, increased vulnerability to UV, and accelerated aging. This process is called "age-related jet lag" and, until last time, was seen as inevitable and irreversible. However, recent research shows some evidence about the possible efficiency of calorie restriction methods, such as intermittent fasting, helping to diminish and prevent circadian skin aging.

Sunburn and Circadian Rhythms

Exposure to the sun without or without non-efficient sun protection leads to skin damage called sunburn. It manifests by inflammation, pain, redness, high body temperature, itching, and delayed skin exfoliation, often followed by the development of dark or less pigmented spots on the skin.

Human skin is more sensitive to ultraviolet damage in the evening, starting in the early afternoon. After the skin is sunburned, it stays in repair mode for 24-48 hours, and it is more vulnerable to ultraviolet and all environmental damage during the day as all protective functions of the skin are diminished.

If you are experiencing a sunburn, you should avoid sun exposure for a couple of days and use moisturizing and protecting skincare during the day, followed by calming and anti-inflammatory skincare during the night. Eat healthy, implement correct sleep patterns, and try to protect your skin more efficiently next time!

Circadian Rhythms and Skin Diseases

Circadian rhythms regulation modulates many skin processes including skin immunity, cell proliferation and differentiation, DNA repair and many others. As it is essential to the skin as well as general human health, circadian rhythm disorders contribute to the development and progression of many, if not all, skin diseases.

There is scientific evidence about a higher risk of skin cancer in people suffering from work-related poor sleep habits, such as night shift work. Delayed sleep phase disorder can play a role not only in cancer initiation but in cancer progression as well. Modern cancer treatment can utilize the circadian clock by modulating the time of treatment for best efficiency, such as using chemotherapy in melanoma treatment in the morning when it is more beneficial.

Circadian rhythm disorder is observed in the majority of psoriasis patients and children with atopic dermatitis, with a significant worsening of symptoms during the nighttime. Scientific progress in circadian biology should help to understand better skin diseases and find new and efficient treatments.

Meder Skincare to Help with Circadian Rhythm Sleep Disorders

Circa-Night Restoring Biohacking Cream

We are especially proud of this multi-awarded product, which was called the best innovation in skincare by Marie-Claire UK Award in 2021 when it was launched on the market. One of Meder's bestsellers, Circa-Night cream activates collagen synthesis and re-folding, specifically for the deep (advanced) sleep phase.

Deep sleep disruption is characteristic of age-related skin changes and leads to loss of elasticity and accelerated development of lines and wrinkles. Using innovative probiotics found in melting glaciers of Swiss mountains and Indian ocean, Dr Tiina Meder created a formulation helping to prevent these skin changes and restore healthy circadian regulation during the night.

As she says: "Circa-Night doesn't help you sleep better, but it definitely helps you look better if you didn't sleep well". Circa-Night cream is suitable for all skin types and genders and is safe to use during pregnancy and breastfeeding period.

We strongly recommend it to everyone experiencing sleep problems, including young parents and people suffering from insomnia. It would be very beneficial if you work night shifts or couldn't establish a regular sleep-wake cycle. Helps to prevent and slow down skin aging if used regularly - we recommend starting to use it regularly after the 40-45 years.

Circa-Hand Restoring Night Cream

Throughout the day, our hands undergo unavoidable fatigue and trauma. While young skin is able to restore itself during a sleep cycle, this restorative ability gradually diminishes with age.

That's where Circa-Hand hand cream comes in, helping to synchronize the circadian clocks of skin cells and repair vital mechanisms of skin regeneration and natural protection. Rich and silky texture of rare Garcinia butter, enriched with olive squalane and vitamin E restores comfort and nourishes dry skin, providing the best care a hand cream can offer.

Potent prebiotics are incorporated to restore microbiome health and enhance the natural resilience of the skin. With just a few weeks of use, you'll notice your skin becoming lighter and dark spots diminishing, thanks to the 4% niacinamide content.

This powerful skin-identical ingredient helps reverse age-related changes in skin pigmentation. All the active ingredients in this hand cream work synergistically to moisturize, nourish, and repair tired skin.

Arma-Bust Cream for Breasts and Décolleté

Arma-Bust cream is formulated as a part of circadian skincare with ingredients such as biofermented soya peptides to help regulate the skin's circadian rhythms, similar to our legendary Circa-Night beauty sleep in a bottle facial cream.

Lightweight formula prevents the formation of chest lines and wrinkles overnight. Kigelia Africana fruit extract, a natural ingredient traditionally used in Africa, is known for its antioxidant and skin-firming properties. This extract has been used to help reduce the appearance of sagging breasts, providing a firmer and more youthful-looking bust.

While Arma-Bust is beneficial as a breastfeeding cream to support your stretching skin, please make sure to remove all cream from your nipple area when you are nursing your baby.

Morning Duo: Energy-Net Cleansing Mask and Energy-Soin Serum

This unique duo of products will help your skin wake-up properly especially if your skin looks fatigued in the morning. Niacinamide helps to activate blood circulation and boosts the synthesis of protective ceramides in the skin, and potent antioxidants restore your skin's natural protection from ultraviolet and air pollution.

Apply a cleansing mask on slightly wet skin and leave on it for 2 minutes (exactly time for perfect teeth brushing!). You can experience a slight pinkness or redness, which is a natural reaction to niacinamide since it boosts healthy blood circulation. Within 10-20 minutes, the redness will subside, leaving your skin naturally firmer, brighter, and healthier.

If you prefer not to experience the temporary redness associated with niacinamide, simply wet your skin with water, apply NRJ-Net cleanser, gently massage for 30 seconds to 1 minute, and rinse with lukewarm water. Wash it off with a lukewarm water and apply Energy-Soin serum on the face and eye area, slightly massaging skin. Now, your skin is fresh and ready for a perfect day functioning!

Night Duo: Net-Apax Cleansing Mask and Soin-Apax Serum

If your skin is sensitive or you are suffering from skin conditions such as psoriasis, eczema, rosacea or others, it would be beneficial to calm skin at night. Prebiotic-based, gentle cleansing mask Net-Apax helps to restore healthy circadian regulation to immune system activity and skin microbiome.

For an extra boost, use Net-Apax as a 2-minute mask. Simply apply, leave on for a couple of minutes, and rinse off. Follow with Soin-Apax serum based on Centella Asiatica extract sourced from Madagascar and Alpine water. It calms down skin, reduces inflammation and help skin to switch to "repair mode" during the night time.