(i) Characteristics of psoriasis in children Psoriasis accounts for 4% of children and adolescents, and several clinical types including the common, erythrodermic, and pustular types are manifested in children. Childhood psoriasis is generally defined as type I, with 2% of cases developing before the age of 2 years. Congenital cases are rare, but most children have a genetic history. The lesions of childhood psoriasis are often more limited and atypical in infancy. The diaper area is usually the initial site of involvement and presents as well-defined red patches without scaling, which should be differentiated from eczema, irritant dermatitis, Candida infection, and diaper dermatitis occurring in this area. Some children with diaper dermatitis will develop psoriasis in adulthood. Plaque psoriasis is the most common type in children and is symmetrically distributed on the extensor side of the elbow and knee joints, with the scalp being the most susceptible site. Facial onset is more common in children than in adults, as are pitting nail changes, nail separation, and hyperkeratosis, which account for 7-40% of adolescents before the age of 18. Children with punctate psoriasis usually have upper respiratory tract infections with positive pharyngeal test cultures and serum streptococcal antibodies, and treatment of respiratory and skin infections can improve psoriasis. Treatment of respiratory and skin infections can improve psoriasis. Most children will develop chronic plaque psoriasis, but it can also resolve spontaneously. Erythrodermic and pustular psoriasis are rare in children. The pustules are superficial and can be limited or generalized. It is often accompanied by general malaise, fever and loss of appetite. Pustular psoriasis can be caused by infections, UVB exposure, oral or topical glucocorticoid medications, and vaccinations. Many infants with pustular psoriasis do not have a history of common psoriasis, but 30% have a history of seborrheic or diaper dermatitis, which should be taken seriously. （Koebner’s phenomenon is more common in children with punctate psoriasis. Most injuries originate from irritation at the diaper site. Therefore, infections and traumatic factors may lead to the development of the disease, so these triggering factors should be avoided as much as possible. Local treatment (1) Emollients For children with mild disease, emollients are routinely applied to stop itching and remove scales for therapeutic purposes. (2) Topical glucocorticosteroids Topical glucocorticosteroid treatment can reduce erythema and flaking, especially for children with mainly pruritic symptoms, which is very effective. These drugs are widely used on the face and scalp. In addition, topical glucocorticoid therapy is often used in combination with other drugs such as carbotriol in children with stable psoriasis. It is generally accepted that topical topical glucocorticosteroids in small doses can avoid rapid drug resistance and the sequelae of long-term application such as skin atrophy and capillary dilation. However, the use of potent glucocorticosteroids in large areas should be considered for suppression of the hypothalamic-pituitary-adrenal axis. Abrupt discontinuation of the drug may lead to rebound of the disease, so the dosage should be gradually reduced when discontinuing the drug. (3) Tar Tar is an effective drug for treating psoriasis in children. Coal tar is the most commonly used, and fish tar and juniper oil are also often used. Coal tar is less irritating and generally does not affect the surrounding healthy skin, and can be used on the face and the flexors of the limbs. (4) Anthralin These drugs tend to irritate healthy skin and should not be used on the face, flexors and genitals. It is also not suitable for use in erythrodermic or pustular psoriasis. Anthralin is indicated for thicker plaques. It should be used under parental supervision. Special care should be taken to protect the surrounding healthy skin with some greasy lubricant. Short contact therapy with anthralin is generally effective, i.e., small doses (0.1 to 0.25%) applied daily for 30 to 45 minutes, and the concentration can be increased to the maximum tolerated concentration (2% to 3%) within a week. (5) Topical vitamin D and its derivatives Compared with other topical treatments, the use of carbotriol in children has been well evaluated. In children aged 3 to 14 years receiving carbotriol (ug/g) twice a day for 8 weeks, psoriatic lesions could be significantly improved, PASI scores were significantly reduced, and serum calcium levels were not affected. However, care should be taken to observe vitamin D levels when extending the treatment period. Generally children should apply carbotriol (50ug/g), and the maximum dose should not exceed 50g/week for children over 6 years old and 75g/week for children over 12 years old. 3. Phototherapy Children with psoriasis are usually exposed to UVB 3 times a week, but the initial dose is based on the minimum amount of erythema assessed by the individual’s degree of sensitivity to light. The dose is gradually increased later. Combined UVB and topical treatments such as coal tar or carbotriol are well tolerated and effective in stable psoriasis. The use of narrow-wave UVB in paediatric psoriasis has been extended from adults, with positive efficacy and low carcinogenic potential. However, it should be noted that PUVA treatment is not suitable for younger children. The most commonly used systemic drugs include retinoids, methotrexate and cyclosporine. These drugs are generally used only for children with pustular, erythrodermic or arthritic psoriasis or those for whom other treatments are ineffective, and parents must be informed of their treatment and the various possible adverse effects as well as the need for long-term monitoring. (1) Retinoic acid Retinoic acid (0.25-0.6 mg/kg) is the commonly used drug of choice, usually for children with severe psoriasis. Smaller doses of retinoic acid are more effective in treating erythrodermic psoriasis than pustular psoriasis. It is important to monitor lipid and liver enzyme levels during treatment. They need to be reviewed monthly initially and every 3 months thereafter. Oral retinoids are generally better tolerated in children than in adults. However, retinoids may cause premature epiphyseal closure and bone scans are recommended every 12-18 months. (2) Methotrexate The efficacy and safety of methotrexate in pediatric patients has not been established. It is generally used in children over 3 years of age, and in children 3 to 16 years of age for the treatment of erythrodermic psoriasis, pustular psoriasis and arthritic psoriasis. The tolerated dose is 0.2 to 0.4 mg/kg, and if gastrointestinal discomfort occurs, it may improve with folic acid. Adverse effects: Basically the same as in adults, attention should be paid to bone marrow suppression, risk of hepatotoxicity and total drug accumulation. Basal complete blood count, liver enzymes and renal function should be measured and monitored throughout the treatment period. In addition, there are several important drugs that interact with methotrexate in children, such as non-steroidal anti-inflammatory drugs, the antimicrobial cotrimoxazole, and the anticonvulsant phenytoin sodium, and concomitant use with antipyretic and analgesic drugs should be avoided in children. (3) Ciclosporin Ciclosporin is less reported in the treatment of psoriasis in children. Only a few children with generalized pustular psoriasis are treated with ciclosporin 3mg/(kg.d), which has achieved good efficacy in the short term, but its long-term efficacy is still inaccurate. The effects of psoriasis on children vary according to their age, personality, disease and adverse drug reactions, and parental attitude, perception and behavior are closely related to the course and severity of the disease.