Complications and their management 1. Pain is a normal response to treatment and usually subsides within 1~3 hours, symptomatic treatment such as cold compresses can be performed. 2. Erythema/edema is a normal response to treatment and can last from a few hours to 3 days. 25% of patients who receive full treatment may develop erythema and edema lasting 24~72 hours. Aggressive postoperative cold compresses can help relieve erythema and edema. 3. Blisters are relatively common and are associated with excessive energy density, improper filter wavelength selection, excessive pulse overlap, or a recent history of skin exposure. Treatment mainly includes cold compresses and topical antibiotic ointment, and short-term oral or topical glucocorticoids if necessary. 4, post-inflammatory hyperpigmentation is mostly seen in darker skin color, sun exposure history before treatment, blisters after treatment or improper setting of treatment parameters. Post-inflammatory hyperpigmentation usually takes 3~6 months to fade slowly and naturally. Chemical exfoliation, topical hydroquinone and other anti-pigmentation drugs can promote hyperpigmentation to subside, and serious cases can try laser treatment. 5, post-inflammatory hypopigmentation is relatively rare, mostly due to pigment cell damage caused by large energy density, can occur in the treatment of blisters, preferably in the forehead. Generally need months or even years to subside, if necessary, can use 308nm excimer laser or narrow wave UVB phototherapy. 6, scabs pigmented lesions often appear after treatment. There is no need to deal with it, and it can be removed naturally, usually takes about 7 days. 7, purpura is common after 515nm filter or shorter pulse width treatment, generally do not need treatment. 8, itchy skin and folliculitis is rare, may be associated with light stimulation of local sebaceous glands, oral antihistamine drugs, topical antibiotics and glucocorticoid preparations. 9, scarring is rare, should be actively dealt with. Atrophic scarring can generally improve on its own, and pulse dye laser or fractional laser can be used to intervene in the early stage. Proliferative scarring is slow to subside, and local injection of glucocorticoid and topical silicone gel can be considered for treatment. Efficacy determination: I. Pigmented skin lesions The color of skin lesions deepens within 5-10 minutes in the treated area. B. Vascular lesions Bright red spots appear in the treated area within a few minutes, and the capillaries disappear or change to blue-gray color. Hairy lesions Edema and erythema around hair follicles. Tips: Although scholars at home and abroad have reported that intense pulsed light is effective in treating melasma, the safety and long-term effect of intense pulsed light on melasma have not been widely recognized because this treatment is usually accompanied by more obvious thermal effect, which may cause aggravation of melasma lesions. Most scholars now believe that IPL is part of the comprehensive treatment of melasma, and that combined with drugs, chemical peels and lasers may benefit patients, while single photon therapy for melasma needs to be cautious, and the treatment parameters should be more conservative long filters (590/615/640 mm), short pulse widths (3-4 ms), and low energies (12-16 J/cm2) may be safer. The endpoint response to treatment is a mild deepening of the color of the lesions and a mild erythematous reaction of the basal skin.