Circadian Biology / Body Clock / Chrono-Skincare
The approximately 24-hour internal biological clock that regulates physiological processes including sleep-wake cycles, hormone secretion, metabolism, immune function and cellular repair. In skin specifically: cell division and DNA repair peak at night; sebum production peaks in the afternoon; cortisol-driven inflammation is highest in the morning; skin permeability is highest at night (30% greater penetration than AM), making PM the optimal time for active ingredients. Disruption of the circadian clock (shift work, irregular sleep, blue light exposure at night) is associated with accelerated aging, impaired immune function, and worsened inflammatory skin conditions.
Practical applications: apply actives (retinoids, acids, AHAs) at night to leverage heightened permeability and peak cell repair activity. Support circadian health with consistent sleep/wake times, morning light exposure, and limiting bright light after 9pm.
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