The principle of picosecond laser is to use a certain wavelength of laser light to irradiate to the surface of the skin and destroy melanin through high energy to achieve the purpose of spot reduction, which is very widely used and suitable for those who have the need of skin rejuvenation and spot removal. Although the effect of picosecond laser is very significant, it also has its disadvantages. Firstly, there is high heat laser irradiation during the treatment process of picosecond laser, and there will be local burning or stinging sensation during the treatment process, which is caused by the absorption of large amount of energy by skin tissue and release of energy, so there may be uncomfortable feeling during the treatment process. Secondly, there will also be skin reactions after picosecond laser treatment. The most common reaction is erythema, and some patients may experience swelling. These reactions are relieved by cold compresses for about a week after the laser procedure and gradually return to normal. In addition, the most common adverse reaction of picosecond laser is post-inflammatory hyperpigmentation. The purpose of doing picosecond laser is to remove spots, but some patients will have post-inflammatory hyperpigmentation after laser treatment in about 2-4 weeks due to local inflammation, i.e., the color will deepen after removing spots.