求翻译：因缺乏对银屑病的发病机理的深入了解，此病目前尚无根治的方法。现有的种种疗法只能起到短期疗效，不能防止复发。轻中度银屑病多使用外用药物治疗，药物有甾体激素、煤焦油、维生素A(视黄醛)和维生素D的衍生物；中重度银屑病的治疗可引入光疗法；对于更严重的病例则需要使用系统治疗药物，如环孢霉素、氨甲蝶呤和口服视黄醛类药物。但上述药物都有些缺陷，如煤焦油使用不方便，而且会引起对紫外线的过敏；甾体激素会引起皮肤变薄等副反应；外用维生素A和D衍生物对皮肤有较强刺激性：口服视黄醛类药物有致畸作用，孕妇禁服。是什么意思？

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Because of the lack of psoriasis The pathogenesis of this disease, an in-depth understanding there is currently no cure. The various therapies available only to the short-term efficacy, it does not prevent recurrence. Mild to moderate psoriasis medication use, NSAIDs drugs, hormones, coal tar produc

Due to lack of in-depth understanding of the pathogenesis of psoriasis, there is currently no cure for this disease. Available to the various therapies can only be short-term, cannot prevent the recurrence. Light in the degrees silver chip disease more using topical drug treatment, drug has steroid