Psoriasis, commonly known as psoriasis, is a common chronic, inflammatory, recurring skin disorder characterized by the appearance of erythematous patches, papules, and plaques of varying sizes covered with silvery-white scales with clear borders, and bleeding spots when the silvery-white scales peel off. It occurs on the scalp, extensor surfaces of the limbs and back. Psoriasis does not directly affect life, but it has a very serious impact on physical health and physical and mental health. The exact cause of psoriasis is not yet clear. At present, it is believed that psoriasis is a polygenic genetic disease in which genetic factors interact with environmental factors and other factors to cause excessive proliferation of keratin-forming cells through T-cell-mediated immune responses. 1, genetic factors epidemiology, HLA analysis and full gene scan analysis studies all support the genetic predisposition of psoriasis. 20% of psoriasis has a family history, when one parent has psoriasis, the incidence of psoriasis in children is about 16%; and when both parents are psoriasis patients, the incidence of psoriasis in children reaches 50%. Class I antigens A1, A13, A28, B13, B17, B37 and Cw6 and class II antigen DR7 of the HLA system are expressed more frequently in psoriasis patients than in normal subjects, with the Cw6 locus being the most clearly associated with psoriasis. Since 1994, eight loci have been identified by genome-wide scans for psoriasis susceptibility genes located in regions such as 1p, lq, 3q, 4q, 6p, 17q and 19p. 2, environmental factors Genetic factors alone are not enough to cause the onset of psoriasis, environmental factors play an important role in triggering and aggravating psoriasis. Factors that can trigger or aggravate psoriasis include infection, mental stress and stressful events, trauma, surgery, pregnancy, smoking and the effects of certain drugs, etc. Infection has always been considered an important factor in triggering or aggravating psoriasis, for example, there is often a history of acute streptococcal infection in the pharynx before the onset of psoriasis, and the condition often improves after antibiotic treatment is given. 3, immune factors Lymphocyte and monocyte infiltration at the lesions of common psoriasis is obvious, especially T-lymphocyte dermal infiltration is an important pathological feature of psoriasis, indicating that the immune system is involved in the occurrence and development of the disease. It is hypothesized that the release of cytokines (IL-1, -6, -8, IFN-γ, etc.) by activated T lymphocytes in the lesions stimulates the proliferation of keratinocytes and promotes and participates in the development of psoriasis. An important feature of the pathophysiology of psoriasis is the accelerated proliferation of keratin-forming cells in the basal layer of the epidermis, the shortening of the mitotic cycle to 37.5 hours, the shortening of the epidermal turnover time to 3-4 days, and the appearance of histopathological incomplete keratinization and disappearance of the granular layer. Second, what are the clinical manifestations of psoriasis? According to the clinical features of psoriasis, it can be divided into common type, arthritic type, pustular type and erythrodermic type, among which common type accounts for more than 97%, and other types are mostly transformed from common psoriasis, which can be induced by the external use of stimulating drugs, systematic use of glucocorticoids, sudden discontinuation of drugs in the process of immunosuppression, as well as infection and mental stress. The initial lesions are red papules or macules, which gradually expand into red plaques with clear boundaries, and can take many forms (such as drip, plaque, coin, map, oyster shell, etc.), covered with thick layers of silvery white scales, scraping away the layers of scales as if lightly scraping wax drops (wax drop phenomenon), scraping away the silvery white scales and seeing light red glowing translucent film (film phenomenon), peeling away the film and seeing Dotted bleeding (Auspitz sign), the latter is caused by the scraping of the tortuous dilated capillaries at the top of the dermal papillae. Wax drop phenomenon, film phenomenon and punctate bleeding have diagnostic value for psoriasis. The lesions can occur all over the body but are most common on the extremities, especially on the elbows, knees and sacral tail, and are often symmetrical, with differences in different parts of the skin. The progressive stage: old lesions do not fade, new lesions keep appearing, infiltrative inflammation of lesions is obvious, surrounded by redness and thick scales; needling, scratching, surgery and other injuries can lead to the appearance of typical psoriasis lesions on damaged areas, called isomorphism or Kobner phenomenon; stationary stage: lesions are stable, no new lesions appear, and inflammation is light. The regressive phase: the lesions shrink or flatten, the inflammation basically subsides, and hypopigmentation or hyperpigmentation is left behind. Acute punctate psoriasis, also known as eruptive psoriasis, is common in young people and often has a history of streptococcal infection of the throat before onset. The lesions are 0.3~0.5cm in size papules and macules, flushed and covered with a few scales, with varying degrees of itchiness. With appropriate treatment, it can subside within a few weeks, and a few patients can be transformed into a chronic course. V. Differential diagnosis of psoriasis Diagnosis and typing are mainly based on typical clinical manifestations, and histopathological manifestations have a certain diagnostic value. Psoriasis should be differentiated from the following diseases 1. seborrheic dermatitis: differentiate from scalp psoriasis. The lesions are erythema with unclear edges. Covered with fine yellow greasy scales, hair can be sparse, thinning, shedding, but no bundle hair. 2. Headache: Differentiate from scalp psoriasis. The damage is covered with grayish white bran-like scales, with hair breakage and hair loss easy to detect fungi, mostly seen in children. The typical lesion is a coppery red, infiltrative rash or maculopapular rash on the palmoplantar area, with positive syphilis seropositivity. 4, flat moss: lesions are polygonal flat purple-red papules, can be fused into scaly plaques, mucous membranes are often involved, the course of the disease is chronic. 5, chronic eczema: differentiate from hypertrophic psoriasis lesions occurring on the lower legs, the extensor side of the forearm and the sacrococcygeal region. Eczema often has intense itching, and the skin is infiltrated with hypertrophic, moss-like changes. Seven, the clinical treatment of psoriasis psoriasis treatment can only achieve clinical remission, not yet a cure. Topical drugs with strong irritation and drugs that can lead to serious adverse reactions (such as systematic use of glucocorticoids and immunosuppressants) should be prohibited in treatment to avoid aggravation of the disease or transformation to other types. The appropriate treatment should be given for different causes, types and stages of the disease, and psychotherapy should be emphasized. Avoid triggering or aggravating factors such as upper respiratory tract infection, exertion and mental tension. The purpose of psoriasis treatment is to control the disease, slow down the process of development to the whole body, reduce symptoms such as erythema, scaling and local patch thickening, stabilize the disease, avoid recurrence, try to avoid side effects and improve the quality of life of patients. Communication with patients and assessment of their conditions during treatment is an important part of treatment. When the effect of single therapy is not obvious in patients with moderate or severe psoriasis, combined, rotating or sequential therapy should be given. Nine, topical drug treatment glucocorticoid cream or ointment has obvious efficacy, should pay attention to its adverse reactions, large area long-term application of strong or super strong preparations can cause systemic adverse reactions, after stopping the drug may even induce pustular or erythrodermic psoriasis; vitamin A acid cream commonly used concentration of 0.025%-0.1%, of which 0.05%-0.01% tazarotene gel treatment plaque type psoriasis efficacy Vitamin D3 derivatives such as calcipotriol also have better efficacy, but should not be used for the face and skin folds; various keratin-enhancing agents (such as tar preparations, anthralin ointment, 10%-15%0 xanthophylline ointment, salicylic acid ointment, etc.) can also be used. Ten, systemic treatment Vitamin A acid drugs are suitable for all types of psoriasis, such as Avelox 0.75~1.0mg/(kg-d) orally; immunosuppressants are mainly suitable for erythrodermic, pustular and arthritic psoriasis commonly used are methotrexate adult dose of 10~25mg per week orally, also available cyclosporine, tacrolimus; patients with obvious infection or generalized pustular psoriasis should use Antibiotics; glucocorticoids are generally not advocated for common psoriasis, but mainly used for erythrodermic psoriasis, acute arthritic psoriasis and generalized pustular psoriasis, etc. The dose can be reduced by combining with immunosuppressants and retinoids, and should be applied for a short period of time and gradually reduced to prevent the condition from rebounding; immunomodulators can be used for those with low cellular immune function. Physical therapy: such as photochemotherapy (PUVA), UVB phototherapy (especially narrow-wave UVB), bath therapy, etc. can be applied.