银屑病与日光照射相关性的机制

银屑病是一种常见的慢性炎症性皮肤病，其发病原因尚未完全清楚，现多归因于遗传与环境因素的交互作用，其中日光作为环境因素的一个方面与银屑病的发病和转归有着明显的相关性。日光中的紫外线可致角质形成细胞凋亡、并能调节机体异常的免疫应答反应从而减轻银屑病的临床症状。日光照射还可促进皮肤合成维生素D，促进角质形成细胞再生。然而，紫外线也是产生活性氧最常见的污染物，如果体内活性氧生成量增加超出机体的抗氧化能力则可能诱发银屑病，部分解释了光敏性银屑病的发生原因。

Mechanisms underlying the relationship between sun exposure and psoriasis

Psoriasis is a common chronic inflammatory skin disease. The nature of psoriasis remains unanswered, and its development is generally attributed to the interaction between environmental and genetic factors. Sunlight, as one of the environmental factors, is closely relevant to the occurence and sequelae of psoriasis. Ultraviolet radiation can induce apoptosis in keratinocytes and modulate abnormal immune responses, and in turn relieve clinical symptoms of psoriasis. Further more, ultraviolet radiation can accelerate the regeneration of keratinocytes by promoting skin to produce vitamin D. However, ultraviolet is the most common pollutant that causes the production of reactive oxygen species. If the production of reactive oxygen species exceeds the antioxidant capacity of the host, psoriasis may be induced, which may partly explain the pathogenesis of photosensitive psoriasis.