(a) What is the etiology of psoriasis? The cause of psoriasis is still unclear. It may be an immune disease mediated by T lymphocytes under the interaction of polygenic genetic factors and environmental factors, and neutrophils, keratinocytes, dendritic cells, endothelial cells and various chemokines are involved in the pathogenesis. Flu, mental stress, seasonal climate, trauma and certain drugs can trigger psoriasis, and smoking, drinking alcohol, eating spicy and other irritating foods may also aggravate the disease. (B) How to diagnose psoriasis? Clinically, we divide psoriasis into common type, joint type, pustular type and erythrodermic type, the most common of which is common type (more than 90%). Psoriasis vulgaris occurs on the scalp and the extremities, mainly manifesting as limited red plaques covered with silvery white scales (Figure 1), and a light red shiny translucent film is visible when the scales are scraped off, and small bleeding dots are visible when the film is scraped off again, white scales, film phenomenon and dotted bleeding phenomenon are the “identity card” of psoriasis vulgaris. In addition, it can invade the glans, the glans and the glans. In addition, it can invade the glans, foreskin and oral cavity, and nail changes such as nail pits, nail cross grooves and nail plate hypertrophy are also very common and can be easily confused with onychomycosis. In addition to the skin lesions of psoriasis vulgaris, it is also associated with painful deformities in the joints and even restricted movement, most commonly in the small joints at the ends of the fingers and toes. The joint symptoms are often aggravated or alleviated by the skin symptoms, and on x-ray the patient has mild hypertrophy of the distal finger joint edges, partly resembling rheumatoid arthritis changes. Psoriatic skin lesions, joint symptoms and negative rheumatoid factor are the basis for diagnosis. In addition, arthritic psoriasis is usually positive for HLA-B27, and together with ankylosing spondylitis and REITER disease is called HLA disease. Pustular psoriasis is rare clinically and is generally classified as generalized or limited. Pustular psoriasis is often associated with the application of corticosteroids or topical irritation during the progressive phase of psoriasis. The onset of generalized pustular psoriasis is rapid, often with dense superficial sterile pustules on top of large erythematous plaques throughout the body, often with high fever, arthralgia, high blood count, and liver and kidney damage. Prior to the use of retinoids, the mortality rate was as high as 50%. Because pustules are sterile and are sometimes aggravated by antibiotics, antibiotics are generally not recommended unless there is clear evidence of infection. Restricted pustular psoriasis is usually limited to the palmoplantar or extremities, and the pustules may dry up and crust over spontaneously, recurring after the scabs fall off, often with pus accumulation under the nail, nail plate loss, or even limb destruction. Erythrodermic psoriasis is often caused by the sudden discontinuation or rapid reduction of glucocorticosteroids after the external use of irritating drugs or long-term heavy use of psoriasis, and is also seen in the receding phase of generalized pustular psoriasis. Patients have diffuse erythematous skin with a large amount of debris, accounting for more than 90% of the body surface area, often accompanied by fever, headache and superficial lymph node enlargement. Due to the destruction of the epidermal barrier, the erythrodermic type is prone to secondary infections, has a high mortality rate, and has a very persistent course. In addition, diseases such as eczema, connective tissue disease, mycosis fungoides or SEZARY syndrome can also present with erythrodermic changes, so patients with erythrodermic disease usually require a skin biopsy to identify the primary cause and provide symptomatic treatment. Different types of psoriasis can be transformed into each other. Ms. Zhang mentioned in the article is a common type of psoriasis, which may also be transformed into an arthritic type after many years. Xiao Yang, on the other hand, started with common psoriasis, was treated with glucocorticoids and developed generalized pustular psoriasis after stopping the medication, and then showed limited pustular psoriasis in between treatments. Psoriasis is not difficult to diagnose through clinical manifestations, rash characteristics, predilection sites and the relationship between onset and seasons, of which observation of the morphology of the lesions is the key. However, the clinical manifestations of some patients are not typical and can be confused with stage II syphilis, discoid lupus erythematosus, seborrheic dermatitis, chronic eczema, neurodermatitis, onychomycosis, REITER disease or rheumatoid arthritis, etc. Skin biopsy and other relevant examinations are needed to determine the diagnosis. In addition, HIV infection with psoriasis-like skin lesions as the first manifestation has been observed in the clinic. (C) How to treat psoriasis? Psoriasis is one of the most common diseases in dermatology, which has a great physical and psychological impact on patients and has a high incidence in Europe and the United States, and related basic and epidemiological research has progressed very rapidly. However, there has never been a cure in clinical treatment, with the main goal of relieving symptoms, clearing skin lesions and prolonging the relapse cycle. For patients with mild to moderate psoriasis vulgaris, topical medications are usually used. Currently, commonly used drugs include vitamin D3 derivatives, retinoic acid cream, salicylic acid ointment, tacrolimus, and white petroleum jelly. Since long-term topical steroid hormones can induce pustular or erythrodermic psoriasis after discontinuation, we do not recommend their use.