1. purpura Purpura or bruising, commonly associated with pulsed dye laser treatment. 595nm, 585nm pulsed dye laser effective energy sign. Patients are informed that purpura is a temporary phenomenon that usually lasts about 1 week. Newer devices for vascular therapy with larger pulse widths and effective energy do not cause the formation of purpura. 2, pigmentation Pigmentation may occur after any laser or intense pulsed light treatment. Most of the pigmentation can fade on its own with time. Excessive hyperpigmentation is most commonly seen with exfoliative laser treatments, especially carbon dioxide laser. It lasts for an average of 3-4 months and is seen mainly in patients with darker skin tones and after skin sunburn. Some pigmented lesions are obvious after laser treatment, such as brownish blue spots, 3, hypopigmentation Hypopigmentation is usually temporary, with melanin as the target color base of laser treatment is more common, especially for tattoo removal treatment, hyperpigmentation lesions and laser hair removal is most common, especially in darker skin tones, after scar treatment, etc. 4, blisters and crust blisters are caused by laser heat damage to the epidermis, such as excessive laser traffic, after sun exposure of the skin to the laser excess and collection. Crusting is common in Q-regulated laser treatment, especially for tattoo removal treatment. The use of high-flow short pulse width and long pulse width of the laser treatment, crusting is to be expected complications. 5, scar scarring is a complication of laser treatment, directly caused by laser heat damage or secondary to infection. Atrophic hypertrophic scars are caused by excessive damage to collagen in the dermis. The risk of scarring is higher with ablative laser treatment, if CO2 or improper selection is used. The number of treatment sessions and energy level per session are important factors affecting scar formation. The use of cooling devices can reduce scarring.