It is the most common vascular malformation, and its incidence has been increasing gradually. The incidence is reported in the literature to be 3% among newborns, and it mainly occurs on the head and neck (80%), with no significant difference between men and women. The cause of PWS is unknown, but some scholars believe that it is due to the lack of nerves innervating the blood vessels at the lesion site, resulting in capillary dilation and congestion, and that PWS initially appears as red or pink patches, which may deepen with age and become bright red and purple, and may thicken to nodularity. The histopathological changes of erythema nodosum are aberrations in the superficial dermal capillary network. The diameter of normal capillaries is only 10μm, and the diameter of PWS dilated vessels varies from 60 to 180μm with the degree of lesion. The average depth of vessels is 460μm±170μm under the epidermis, and the endothelial cells of malformed vessels have no proliferation, and the walls of the vessels are still composed of single layer of endothelial cells, and the surface of the lesion layer is covered with normal epidermal layer. Before the introduction of laser treatment for vivid nevus, vivid nevus can only be disguised by make-up, and isotope treatment has been applied in medicine, but it often leaves untreatable scar, which brings trouble to future treatment; plastic surgery adopts the method of surgical excision and suture, which is still effective for smaller vivid nevus, but also leaves scar; larger vivid nevus needs skin implant or application of flap repair, not to mention that it has to leave unsightly scar in the It is not until the introduction of adjustable pulsed dye laser in recent years that hope has been brought to the treatment of nevus of bright redness. On the one hand, the output wavelength of laser can be absorbed by hemoglobin, on the other hand, because of the selective photothermolysis, it avoids the concentration of heat, thus reducing the damage to the skin, and can achieve the more ideal treatment effect of no scar fading. Usually patients are most concerned about the number of treatments needed to heal, which is honestly a difficult question to answer accurately. Because there are three types and six grades. (1) pink type, erythema is pink in color, this kind is mostly seen in children, the degree of lesion belongs to grade 1, such as dark red is grade 2, dark red is grade 3; (2) purple red type, erythema is purple in color, mostly seen in adults, according to the color shades can be divided into light purple and dark purple, the degree of lesion belongs to grade 4 and 5; (3) thickening type erythema is mostly dark purple, the surface is thickened, can slightly protrude from the skin, serious cases can have warty nodules on the surface It is easy to bleed after touching and is often itchy. It is mostly seen in older people, and the lesion grading belongs to grade 6. The correct lesion classification and grading is an important basis for determining the dose of irradiation and the amount of photosensitizer administered during treatment. Each laser treatment can only partially close the blood vessels, and a few blood vessels may recanalize after the treatment, so the treatment usually needs to be divided into several sessions, and the interval between each session should not be less than two months. In addition, there are great individual differences in the response of the body to laser treatment (that is to say, the same physician with the same equipment, using the same treatment conditions, treatment of the same red birthmark, each person’s treatment response is different), coupled with the fact that each patient’s condition is light and heavy (some are only mild erythema-like, hand pressure on the lesions will disappear, while some people have purplish red lesions, hand pressure does not fade, and even higher than the skin surface Therefore, the number of treatments for each person varies greatly from individual to individual. Some lighter patients may only need 3-4 treatments, while others may need 6-7 treatments or even more. Although laser treatment for nevus is the most effective and recognized way, there are patients who cannot be cured, when is the best time for treatment? Clinically, the younger the age, the better the treatment. There are several reasons for this, mainly related to the developmental characteristics of nevus. Firstly, the skin thickens with age, which is not conducive to laser penetration of deep lesions; secondly, the vascular lesions also thicken with age, which is not conducive to effective elimination; furthermore, the vascular diameter thickens with age, which reduces the possibility of eliminating the nevus. The older the patient is, the larger the area of the nevus and the deeper the lesion will be, so it is difficult to grasp the scale of laser treatment, and there is a possibility of leaving scars or incomplete removal. Patients with thickened skin or patients who are difficult to treat need to change to photodynamic treatment, which is to inject photosensitizer before applying laser treatment. It can be seen that for the bright red nevus, it is necessary to treat it early and cooperate with the doctor’s treatment plan in order to achieve the desire of cure, or at least to control the development of the disease by laser.