Circadian rhythms and atopic dermatitis

The circadian rhythm is a 24-hour periodic cycle determined by the Earth’s rotation that modulates the behavior, physiology, and metabolism of all living organisms on our planet. The system that controls the circadian rhythm is known as the circadian clock. The mechanism of the circadian clock plays a crucial role in organismal development and functioning. For a long time, circadian clocks operated normally, being dependent on the alternation of light and darkness; however, lifestyle changes (artificial lighting, electronic devices, mobile phones, television, long-distance flights, etc.) have profoundly affected circadian rhythms. The resulting disruptions have led to health problems considered significant in the development of a number of diseases (malignant tumors, cardiovascular diseases, metabolic disorders, obesity, immune dysfunction). In the skin, circadian rhythms are reflected in daily changes in transepidermal water loss, permeability and microcirculatory function, pruritus intensity, sleep–wake cycle, and the activity of the innate and adaptive immune systems. At the cellular level, the circadian rhythm regulates the mitotic cell cycle, keratinocyte differentiation timing, and many other processes. In atopic dermatitis, a vicious cycle exists: pruritus worsens sleep quality, leading to chronic stress, thereby disrupting the sleep–wake circadian rhythm; in turn, sleep deprivation, poor sleep quality, and chronic stress aggravate pruritus. These processes trigger exacerbations of atopic dermatitis, in which both pruritus and poor sleep quality intensify, significantly impairing the rhythmic functioning of the whole body and the skin in particular. Recognizing the importance of circadian skin functions and the consequences of their disruption allows physicians to optimize therapy and maximize efficacy of prescribed treatment. Many topical agents may provide greater benefit if circadian rhythms are taken into account, whereas lower doses or less potent formulations could be sufficient.