According to the causes and appearance of scar formation, scars can be basically divided into the following categories: 1, superficial scar: the injury only hurts the superficial layer of epidermis or dermis, which is slightly uneven, often accompanied by different degrees of pigmentation, local softness and flatness, and generally no dysfunction, which can be improved by grinding or dot matrix laser treatment; 2. Hypertrophic scar: Once serious skin injury involves deep dermis, it is possible to form hypertrophic scar. It is characterized by the thickening and protrusion of scar tissue on the skin surface, which is red in the early stage due to congestion, often accompanied by pain and itching. Hypertrophic scars on the joints of the neck and limbs often affect the activities of the joints and must be surgically removed. 3. Atrophic scar: It often occurs after long-term ulcer wound healing, or in parts with less subcutaneous tissue, such as scalp and tibia. Scars are thin, flat or slightly higher than the skin surface, and can be closely attached to deep tissues, showing reddish or white color, and the epidermis is extremely thin, which is easy to repeatedly rupture to form ulcers and even local cancer. 4, contracture scar: scar hyperplasia, hardening, and then contracture, occurring at the joints of the limbs will lead to the joints can not be completely straightened, contracture scar can not raise the head in the neck, must be surgically resolved. 5, keloid: It is a special type of scar, which mostly occurs in the chest, shoulders and back, and the earlobe goes through the ear hole. It is often manifested as a hard scar that obviously protrudes from the skin surface, causing pain and itching, and will gradually grow up and even invade normal tissues. Keloid has the characteristics of refractory and high recurrence rate, which can only be improved by comprehensive treatment. 6. Linear scar: It is the most common scar in clinic, which is mostly caused by scratches, cuts and knife wounds. It shows linear scar tissues with different lengths and widths, which can be repaired by plastic surgery. 7. Flake scar: mostly caused by abrasions, burns, skin avulsion, etc. It is characterized by pieces of scar tissue, which can proliferate, thicken and contract, and can be repaired by repeated resection or implantation of dilator.