Psoriasis is an immune-mediated genetic skin disease. The underlying pathomechanisms involve complex interaction between the innate and adaptive immune system. T cells interact with dendritic cells, macrophages, and keratinocytes, which can be mediated by their secreted cytokines. In the past decade, biologics targeting tumor necrosis factor-α, interleukin (IL)-23, and IL-17 have been developed and approved for the treatment of psoriasis. These biologics have dramatically changed the treatment and management of psoriasis. In contrast, various triggering factors can elicit the disease in genetically predisposed individuals. Recent studies suggest that the exacerbation of psoriasis can lead to systemic inflammation and cardiovascular comorbidity. In addition, psoriasis may be associated with other auto-inflammatory and auto-immune diseases. In this review, we summarize the risk factors, which can be divided into two groups (namely, extrinsic and intrinsic risk factors), responsible for the onset and exacerbation of psoriasis in order to facilitate its prevention.

Skin is the largest and most complex organ in the human body comprised of multiple layers with different types of cells. Different kinds of environmental stressors, for example, ultraviolet radiation (UVR), temperature, air pollutants, smoking, and diet, accelerate skin aging by stimulating inflammatory molecules. Skin aging caused by UVR is characterized by loss of elasticity, fine lines, wrinkles, reduced epidermal and dermal components, increased epidermal permeability, delayed wound healing, and approximately 90% of skin aging. These external factors can cause aging through reactive oxygen species (ROS)-mediated inflammation, as well as aged skin is a source of circulatory inflammatory molecules which accelerate skin aging and cause aging-related diseases. This review article focuses on the inflammatory pathways associated with UVR-mediated skin aging.

In Japan, the Japanese Society for Psoriasis Research (JSPR) has been conducting annual epidemiological surveys of patients with psoriasis since 1982. The aim of this study was to conduct a recent epidemiological analysis of the psoriasis patients who were enrolled in the JSPR from 2013 to 2018. A total of 15 287 cases were enrolled from 132 medical institutions, out of which 65.3% (9989 cases) were male and 34.7% (5298 cases) were female. Approximately 50.0% of the cases had past history and comorbidities, such as hypertension (42.0%), dyslipidemia (30.0%), diabetes mellitus (23.7%), hyperuricemia (15.1%), cardiovascular disease (6.0%), and cerebral vascular disorders (6.0%). There was a yearly increase in the use of corticosteroid/vitamin D₃ combinations and apremilast for treating psoriasis. In contrast, the use of phototherapy gradually decreased. From 2013 to 2018, approximately 18.6% of the cases were treated with biologics, such as infliximab (17.6%), adalimumab (23.3%), ustekinumab (21.4%), secukinumab (11.6%), ixekizumab (7.6%), brodalumab (6.3%), and guselkumab (4.3%). In the past decade, the biologics have changed the treatment and management of psoriasis. This survey includes significant information regarding the recent perspective of psoriasis in the Japanese Society, especially focusing on the treatment trends after the introduction of biologics.