The concept of pathological scar is also called abnormal scar, which is relative to normal scar. Hypertrophic scar (HS) and keloid (K) are collectively called pathological scar. Scars with similar texture to the surrounding skin are called normal scars or mature scars. Pathological scar is a kind of skin fibrosis disease, which has excessive production and deposition of a large number of connective tissue matrix such as collagen. The importance and harmfulness of scars are inevitable products in the process of human trauma repair. Broadly speaking, there is no wound healing without scars. The main component of scar tissue is fibrin. The production and deposition of collagen in scar tissue increases the strength of the wound, which is beneficial in general. If the scar tissue is not completely formed, the damaged tissue can't get normal tension, which will lead to many complications, such as the scar healed by abdominal incision is weak, and under the action of intra-abdominal pressure, the scar can be re-opened or the abdominal contents gradually swell out, forming abdominal hernia. On the contrary, if the scar is excessively formed, it will always lead to serious appearance or function problems. The harm of scar depends on its essence and characteristics, as well as its secondary fixation of deep tissue. Therefore, compared with the tissue before injury, scar is always an imperfect substitute. From the mechanical point of view, its strength resistance is weakened; From the point of view of nutrition, it creates obstacles to the exchange of oxygen and nutrients; Functionally, it causes deformity and dysfunction of damaged tissues, and aesthetically, it destroys the appearance. Third, the clinical manifestations and classification of scars According to histological and clinical differences, scars can be divided into the following types: ① Hypertrophic scars. This kind of scar mostly occurs after the wound of deep burn heals. Reticular hypertrophic scar is also common in the suture around the third-degree burn wound after skin grafting. In addition, the most common is that any scar after suture also belongs to this category. Hypertrophic scar is characterized by prominent surface, irregular shape, unevenness, flushing and congestion, and tough texture. There is burning pain and itching. Hypertrophic scar is characterized by rising ambient temperature, emotional excitement, or aggravated symptoms when eating spicy and irritating food. Hypertrophic scars usually last for months or years before they gradually degenerate. This kind of scar is characterized by early local swelling, hardening and congestion. The surface of its tissue structure is covered by a layer of atrophic epithelial cells, with vasodilation and inflammatory cell infiltration in the middle layer, less collagen fibers in the bottom layer and a large number of connective tissue hyperplasia. This kind of scar is higher than the skin surface, and it thickens and hardens locally in the early stage. The capillaries are red or dark red with congestion. Generally, the base of scar is not attached to deep tissue, so it can be pushed and squeezed, and its contractility is small. Most of them will not cause serious dysfunction, but it will affect the beauty of face and exposed parts, so it often needs treatment. ② Keloid Keloid is essentially a connective tissue tumor on the skin, and it is a kind of scar characterized by persistent and powerful proliferation. It is often manifested as the image of crab feet infiltrating into the surrounding healthy skin, and the skin lesions protrude from the skin surface, uneven, irregular and hard. I feel itchy and unbearable. Characteristics of keloid: 1. Systematic factors may play a major role, especially specific physical factors, sometimes showing genetic characteristics. Keloid of this kind of patients often has no obvious relationship with the severity of skin injury. Even small trauma, such as mosquito bites, vaccination and other acupuncture injuries, can form keloid. 2. Racial differences: According to statistical analysis, the incidence of keloid in people with darker skin color is 6-9 times higher, which may be related to abnormal metabolism of melanocyte stimulating hormone. 3. Significant predilection sites: common in sternum, deltoid muscle, auricle, mandible and upper back. 4. The lesion is very long and grows for many years. With the progress of the lesion, the scar gradually infiltrated and spread beyond the original basement and spread to the surrounding normal skin. 5. It is easy to relapse after simple surgical resection and suture treatment, and the stronger the proliferative power, the larger the scar area and the faster the growth rate. Therefore, arbitrary surgical resection is not allowed. Keloid is common in the upper neck, ears, chest, shoulders and upper arms. Female sternum is the most common part, which is related to the weight pulling and breathing movement of both breasts. At present, the etiology of keloid is unknown, which may be related to the special qualities of human beings, that is, the so-called scar constitution. In addition, chronic infection and chemical stimulation are also factors that cause pain. In addition, it is also related to family inheritance. ③ Superficial scar This refers to a kind of scar on the surface of skin, which is mostly caused by slight skin abrasion or superficial burn (superficial dermis). Its appearance is slightly different from normal skin, with rough surface or pigment change, and generally no dysfunction. As time goes on, scars will gradually become inconspicuous, so this kind of scar generally does not need treatment. ④ Atrophic scar is one of the most unstable scar tissues, also known as unstable scar. It is common in large-area burns, especially wounds that go deep into the fat layer. Wound healing only depends on the growth of surrounding epithelial cells without skin grafting. In addition, the healing of chronic ulcers in the lower leg or other parts after long-term treatment is also a scar of this nature. This kind of scar is characterized by thin epidermis, flat surface, poor local blood circulation, bright white and hard base. Because its surface layer is only covered with a layer of atrophic epithelial cells, it can not withstand external friction, and it is often easy to rupture and form ulcers, which is generally difficult to heal and can lead to malignant transformation for a long time. Therefore, it is a kind of scar that often adheres to the underlying muscles, nerves and blood vessels, and has great contractility, so it can stretch normal tissues, causing more serious dysfunction than hypertrophic scars. Because this kind of scar is very destructive, we should pay attention to prevention, transplant skin as soon as possible, and don't let it heal itself. ⑤ Contraction scar is a scar named after its dysfunction. It is more common after deep burn healing. Because of scar contraction, it often leads to appearance change and dysfunction. Long-term scar contracture will affect the development of bones, muscles, blood vessels, nerves and other tissues, and should be treated as soon as possible. The common deformities caused by scar contracture in clinic include ectropion of eyelid, ectropion of lip, chin-chest adhesion, scar contracture of hand and flexion or extension contracture of each joint. Among them, the cord-like scar contracture of the flexion surface of the joint, if it takes a long time, the skin and subcutaneous tissue on both sides of the contracture scar can be gradually elongated and become webbed scar contracture, which is called webbed contracture scar. This kind of reticular scar is common in the front of neck, armpit, elbow fossa, ankle joint and so on. The smaller ones can be found in inner canthus, outer canthus, nasolabial groove, squab, webbed fingers and other parts, and some appear in a ring shape at the opening of body surface pores, which leads to the narrowing of its caliber and affects its normal function. Reticular contracture scar can be repaired by Z plasty. ⑥ Depressed scar When scar tissue causes depression deformity on the body surface, it is called depressed scar. It is common in scars left after smallpox, chickenpox or acne, and can also be seen in patients with trauma and skin infection. Simple concave scars are only linear scars and depressions in their areas, while extensive concave scars can be combined with subcutaneous tissue, muscle or bone tissue defects. The scar base is attached to the deep muscle or tendon. To correct this deformity, we should not only deal with the scar on the skin, but also adopt different methods to repair the defect and restore the normal appearance according to the degree of depression. ⑦ Scar cancer Scar tissue becomes hateful and becomes scar cancer. Scar cancer mostly occurs in contracture scars formed by burns. It often occurs in the adjacent parts of joints. Because of the constant pulling of joint activity, the scar breaks repeatedly and eventually becomes cancerous. Scar cancer can also originate from the scar tissue of chronic ulcer of lower limbs or the sinus of chronic osteomyelitis. Scar cancers are mostly fully differentiated squamous cell carcinomas. Lymphatic metastasis is the main form, while hematogenous metastasis is rare.