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The Science of Circadian Rhythms

The Circadia name derives from the two Latin words circa diem, meaning “around the day.” The word “circadian” refers to a 24-hour cycle and describes rhythmic changes in our physiology and behavior. When these biological rhythms are disrupted or disordered, they can adversely affect our health, appearance, and well-being.

Circadian rhythms were developed over millions of years, controlled by the daily light-dark cycle created by the earth turning on its axis. Studies have found that a biological “clock” is in several parts of the brain, establishing these circadian rhythms in mammals. It has been determined that these “clocks” consist of an array of genes that regulate physiological processes throughout the body. We know that the central circadian clock is in the hypothalamus in the brain. Its primary function is to synchronize the clocks in the peripheral tissues, the skin being one of these, and it appears that all types of skin cells contain some form of a circadian clock.

It is essential to understand that the daily rhythms are not just a response to changes in light and dark produced by the earth’s spinning motion but a response to the timekeeping system within the body. It is this system which allows the organism to adjust and anticipate changes that are associated with day and night. Why is this so important? Consider that if the urge to sleep comes during the light portion of the day, many animals would be vulnerable to predators. Anyone who’s ever traveled across several continents is familiar with jet lag, a profound biological clock disruption. The extreme importance of these phenomena has led to the development of a new science associated with the effects of time on the body. This new science is called chronobiology. At Circadia, we focus on the impact of chronobiology and circadian rhythms on the skin. 

Circadian Rhythms and the Skin

The concept of circadian rhythm isn’t new. It started in the 1700s with the French scientist de Mairan, who published a paper describing the peculiar movement of leaves in plants during

the day. They would rise during the day and fall at night. He put these plants in a room when they were not exposed to sunlight, and he saw the same phenomenon. He concluded that this movement had something to do with a mechanism inside the plant and whatever effect the sun may have.

A recent study reveals the importance of the biological clock in regenerating skin stem cells. When disrupted, this system results in premature tissue aging and a greater predisposition to developing skin tumors.

Since the skin is exposed to the sun’s ultraviolet rays and bacteria and viruses, one of the skin’s primary functions is to protect the individual from these potential dangers. When the biological clock works well, stem cells, which constantly replace damaged tissue, can divide at a time that  would allow minimum exposure to damaging ultraviolet light.

When skin cells divide, in a process called proliferation, their DNA is more susceptible to ultraviolet damage since it is extended within the process of cell division. It is well known that the proliferation process occurs during the day at various times. However, it happens at least 30 times more rapidly at night than during the day. Associated with proliferation are such critical functions as the rate of water loss and blood flow, which are 20 to 30 percent higher at night than in the morning or afternoon. Circadian rhythms in the skin affect the biology of appearance and profoundly affect the absorption of applied treatment products. 

Regulation of the skin barrier properties, such as transepidermal water loss and skin hydration, as well as skin pH and temperature, are controlled by the circadian clocks. Therefore, skin care professionals should be aware of the time of the day when they assess the skin or perform a specific treatment. The time that the assessment is made and the time that the treatment is applied will significantly affect the efficacy of the product or the correctness of the diagnosis.

Peggy Janich, Gloria Pascual, Anna Merlos-Suárez, Eduard Batlle, Jürgen Ripperger, Urs Albrecht, Karl Obrietan, Luciano Di Croce, Salvador Aznar Benitah. The circadian molecular clock creates epidermal stem cell heterogeneity. Nature, 2011; DOI: 10.1038/nature10649
Geyfman M, Andersen B. How the skin can tell time. J Invest Dermatol. 2009 May;129(5):1063-6.
Yosipovitch, G, Xiong, GL, Haus, E, Sackett-Lundeen, L, Ashkenazi, I, Maibach, HI, Time- dependent variations of the skin barrier function in humans: transepidermal water loss, stratum corneum hydration, skin surface pH, and skin temperature. J Invest Dermatol, 1998 110, 20–23.