INTRODUCTION
Acne vulgaris, a common skin disorder affecting more than 40 million persons in the US, with as many as 90% of adolescents suffering from some degree of acne,1 and surveys of adults, place the incidence as high as 26-51% well into the fourth decade.2 Although the precise pathophysiological mechanisms remain obscure, acne is characterized by inflammation of pilosebaceous follicles, which in its most severe form results in cyst and nodule formation leading to permanent scarring.
Aside from the physical features of the disease, acne vulgaris is often associated with significant psychological morbidity3 and in some cases even mortality due to suicide.4 The association of acne and psychological disorders, particularly depression and anxiety, are reportedly more severe in acne patients than in many other serious chronic, nonpsychiatric medical conditions.5
A causal association between acne and psychosocial comorbidities has been suggested in the past. Indeed, almost a century ago it was postulated that a systemic inflammatory response may link acne to other co-occurring disease
processes, including emotional disorders.6 However, a compelling mechanistic link between the seemingly distinct physiological processes has yet to be confirmed by experimental or clinical research.
Previous studies have certainly shed light on the role of inflammation in the acne process. The earliest detectable lesion in the pathogenesis of acne vulgaris is the microcomedone, which is characterized by hypercornification and hyperkeratinization within the pilosebaceous infundibulum and in turn plug formation within the follicle. While the inciting event behind this change in infundibular architecture remains unknown, in vitro experiments have suggested that the inflammatory cytokine IL-1α may play a significant role. Follicles stimulated with IL-1α in vitro have been observed to undergo histologic changes (hypercornification) consistent with those seen in comedone formation, and this effect has been attenuated experimentally via blockade of the IL-1 receptors.7,8
Propionibacterium acnes, a species of bacteria that is commonly associated with the development of acne, has also been shown to stimulate IL-1α production from keratinocytes in vitro,