Your Skin’s Circadian Rhythm

Most of us are aware of the circadian rhythm in our bodies that occurs over the course of a 24 hour period. But do you recognize that your skin also experiences a similar circadian rhythm?

Circadian rhythm is the body’s inherent physiologic, behavioral, and metabolic processes that occur over a 24-hour period; it is significantly influenced by light and our surroundings.

Melatonin is the primary compound involved in regulation of our circadian rhythms; levels of this substance fluctuate throughout the course of the day at lower levels and tend to increase at night. Melatonin is an antioxidant and is linked to hair growth, controlling ultraviolet damage in skin cells, and healing of wounds.

When our circadian rhythm is interrupted, the result is a disruption in the natural biologic routines of our bodies. Within the skin, this can manifest as increased water loss, unhealthy proliferation of skin cells, and interruption of the ability of our skin to repair DNA damage (which typically occurs at night). As dermatologists, we take this cycle into consideration when determining when to apply certain products to the skin, i.e. sunscreens in the morning and repairing serums at night).

This information underscores the importance of adequate sleep in maintaining optimal skin health. Our skin cells actually contain clock genes which ebb and flow in regard to water loss from the skin to the surrounding environment, blood flow, growth of new skin cells, and skin temperature. Our skin loses more water at night when it becomes more permeable. This can cause our skin to feel dry, dehydrated, irritated, or itchy; and we may be more aware of this at night or when we wake up in the morning. Alternatively, night time is an ideal time to apply creams and serums that we want to penetrate into our skin to achieve maximum result.

Blood flow in our skin increases in late afternoon and evening; this can also affect absorption and efficacy of topical creams, lotions, and medications that are applied to the skin during this time with increased absorption and diffusion into the surrounding tissue as blood flow increases. Our skin temperature is also regulated in a cyclic way with temperatures in the skin reaching a peak in the afternoon and then dropping at night.

Skin cell proliferation peaks around midnight in healthy skin cells. Cancerous skin cells lose this rhythm and may continue to proliferate in a more unregulated way. Oil producing glands also show a rhythmic pattern with minimal activity in the very early morning and increased activity at midday.

The fact that our cortisol levels fluctuate throughout the day is well-recognized with a natural trough in the evening. As cortisol levels drop, we may experience increased skin sensitivity, itching sensations, and greater inflammation in our skin.

Numerous studies support the conclusion that when our natural sleep/wake cycles are interrupted, there is an increased cancer risk. This is demonstrated in individuals whose careers require nighttime work such as night shift workers, pilots, and flight attendants.

Consideration of your skin’s circadian rhythm is important to optimize skin health and also increase efficacy of skin care products in achieving the best results for your skin.

Source: Lyons, Alexis B et al. Circadian Rhythm and the Skin: A Review of the Literature. Journal of Clinical and Aesthetic Dermatology. Sept 2019, vol 12 (9): 42-45.

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