We continue with a focus onwhen possible, as well as clinical studies that may shed light on how to time skin care treatments.
It is important to remember that several studies in the last 20 years have revealed cutaneous tendencies based on the time of day. For instance, sebum production is known to be highest around noon, and pH also peaks during the day and is at its lowest at night.1-5
In 2019, Dong and associates showed that blue light at 410 nm reduces PER1 transcription in keratinocytes, indicating that epidermal cells have the capacity to directly sense light and regulate their own clock gene expression. With the introduction of blue light at night, circadian rhythm is disrupted as epidermal skin cells act as if it is daytime. The investigators also considered blue light–induced damage to skin cells at various doses and exposure times in comparison with cells that remained unexposed to light. The production of reactive oxygen species increased in the exposed cells, as did DNA impairment and the emergence of inflammatory mediators, all of which have the potential to hasten aging.6
Early this year, Dong and associates demonstrated that melatonin can dose-dependently stimulate PER1 clock gene expression in normal human dermal fibroblasts and normal human epidermal keratinocytes, and verified that the MT-1 melatonin receptor in such fibroblasts manifests a marked decline with age. The researchers concluded that the melatonin pathway contributes significantly in cutaneous aging and impairment, and that its relationship with skin circadian rhythm points to a possible role in slowing the rate of skin aging through the modulation of cutaneous melatonin receptors.7
In 2019, Walker and associates investigated the effects of dim artificial light at night on wound healing in female C57BL/6 mice, and found that those conditions prior to wounding reduced healing. They concluded that such information might warrant consideration in prescribing treatment.8
Vaughn and associates contended that alterations in circadian rhythm may contribute to the development of atopic dermatitis.9 A good example of the impact of circadian rhythms on cutaneous health is the nocturnal exacerbation of atopic dermatitis, particularly in children.10
According to Plikus and associates, recent evidence has emerged showing that the circadian clock regulates UVB-induced DNA damage and cutaneous cancers, and it is also associated with the immune-mediated disorder psoriasis.11
In 2018, Deshayes and associates conducted a clinical study to evaluate the precursors and stem cell attributes of hHF (human hair follicle keratinocytes), hEpi (human interfollicular epidermal keratinocytes), and hHFDP (hair follicle dermal papilla stem cells) in response to clock pathway changes caused by long-term deregulation of circadian rhythms. A total of 20 women participated in the study, 10 in each group (day workers were the control group and compared with shift workers). Two 3-mm fresh punch biopsies were collected from the occipital region of each participant. The investigators reported that chronic circadian rhythm deregulation influenced clock pathway protein expression and correlated with changes in hHF, hEpi, and hHFDP. They concluded that their findings represented the first data in humans suggesting that deregulation of the clock pathway modulates regenerative activity in human cutaneous and hair precursor cells.12
Later that year, Wu and associates reported on the role of the circadian clock in the transcriptional regulation of human epidermis. Investigators sampled 20 human participants through a 24-hour period and a population of 219 people once, finding a potent circadian oscillator in human epidermis at the population level, hundreds of rhythmically expressed genes, as well as a biomarker set for human epidermis that can, with one sample, highlight circadian phase within a 3-hour time frame. The team concluded that rhythms in human epidermis persist at the population level, and that they were able to present an effective single-sample circadian biomarker.13 This is important, as Morris pointed out, because the standard practice for measuring an individual’s internal clock is to use a dim-light melatonin onset assay over the course of a day.14 In 2019, Jia and associates studied the skin surface lipid profiles of young women to evaluate and characterize circadian human facial surface lipid composition. The investigators identified significant markers of circadian rhythm, with glycerolipids most affected. They ascribed changes in skin barrier function, such as variable pH and transepidermal water loss, to alterations in triacylglycerol levels as well as free fatty acid chain lengths and content that were affected by variations in circadian rhythm.15
Sleep and the timing of topicals
Based on their recent review of the literature on circadian rhythm and skin, Lyons and associates argued that an understanding of circadian rhythm helps dermatologists in recommending the optimal times for patients to apply topical medications. They added that urging patients to get sufficient sleep is important because DNA repair of the skin occurs best at that time.16
Doctors have known for half a century that timing drug delivery to a patient’s circadian clock can enhance outcomes. Chronobiological research into how circadian rhythms work at the cellular level, and in cutaneous cells in particular, is a fascinating and expanding area of inquiry that could help dermatologists more accurately recommend timing for skin care regimens. Much more research, especially in clinical trials, is necessary to further elucidate how to best work with the skin’s natural rhythms.
1. Mehling A et al..
2. Latreille J et al..
3. Le Fur I et al..
4. Verschoore M et al..
5. Yosipovitch G et al..
6. Dong K et al..
7. Dong K et al..
8. Walker WH II et al..
9. Vaughn AR et al..
10. Fishbein AB et al..
11. Plikus MV et al..
12. Deshayes N et al..
13. Wu G et al..
14. Morris A..
15. Jia Y et al..
16. Lyons AB et al.