24-hour period of time known as the circadian rhythm [1]. This central “clock” regulates normal functioning by coordinating with peripheral “clocks” that are expressed in cells throughout the body, including the skin [2–6]. In the skin, temperature variations, pH, barrier function, and transepidermal water loss have been shown to vary depending on the time of day [7]. Previous work by our group has demonstrated that poor sleep quality is associated with increases in signs of intrinsic skin aging, poor skin barrier repair, and poor perceptions of appearance [8]. However, the mechanisms behind our findings remain unclear and may be the result of increased oxidative stress secondary to poor sleep [9,10]. Sleep and its impact on inflammatory skin conditions has also been alluded to in psoriatic animal models wherein acute Clocks&Sleep 2019, 1, 510–516; doi:10.3390/clockssleep1040039 www.mdpi.com/journal/clockssleep Clocks&Sleep 2019, 1 511 sleep deprivation was linked to worsening psoriatic inflammation; however, data evaluating sleep in the context of human inflammatory skin disorders, including acne vulgaris (acne), is limited [11]. 12% of adult females. Its pathogenesis involves follicular hyperkeratinization, inflammation, in part generated by Cutibacterium acnes (formerly Proprionibacterium acnes) and hormonal alterations [12]. In a French study, fatigue upon waking and acne were shown to be strongly correlated [13]. Prior studies have also suggested a bi-directional relationship between sleep and acne [14,15]. In this study, we attempted to further elucidate the connection between sleep and acne. Forty subjects were enrolled in our study, with the majority being female (82.5%) and white (57.5%). Thirty subjects (75%) were actively being treated for acne at the time of the study, and only three (7.5%) were previously diagnosed with a sleep disorder. As determined by the Global Acne Grading Scale (GAGS), acne severity of our cohort ranged from mild to severe, with the majority of subjects being classified as mild (n = 21), followed by moderate (n = 17); two were classified as severe. Thirty subjects scored a 5 or greater on the Pittsburgh Sleep Quality Index (PSQI) indicating poor sleep quality. Demographic and acne/sleep characteristics of the population are detailed in .Sociodemographic and outcome variables of the study population. cient (r) showed several statistically significant 3. Discussion Our study showed that, on univariate analysis, self-reported acne severity scores are directly correlated with poorer quality of life and depressive symptoms (DLQI: r = 0.44677, p = 0.0039; PHQ-2: r = 0.33512, p = 0.0345). On multivariate analysis, when controlling for DLQI and PHQ-2, the average subjective sleep score decreased (i.e., worsened) as the objective acne severity score (GAGS) increased and vice versa (p = 0.0306, parameter estimate = 0.09003). In 2015, a French study demonstrated that there is a strong positive correlation between acne and fatigue upon waking (i.e., poor sleep quality) even when adjusting for age (p < 0.0001). It also demonstrated stressed patients have greater fatigue upon waking (p < 0.0001) and are more likely to have acne (OR = 1.975; p < 0.0001) [13].Although fatigue may be a symptom of depression and patients whose quality of life has been more severely impacted by acne are more stressed, our research demonstrates that, when controlling for depressive symptoms and quality of life impact, subjectively worse sleep quality is associated with objectively worse acne [13,16]. This suggests that there may be an influence of acne severity on subjective sleep quality and vice versa, confirming prior findings of the impact acne has on quality of life and mental health. Our data did not establish a correlation between the PSQI and either subjective (r = 0.19349, p = 0.2316) or objective (GAGS; r = 0.14822, p = 0.3614) scores of acne severity. There was also no correlation (p = 0.2271) between the PSQI and GAGS even when controlling for the DLQI and PHQ-2 like there was for average subjective sleep scores and GAGS. In addition, it is interesting to note that there was no correlation (r = 0.21182, p = 0.1895) between self-reported acne severity and GAGS,