A scar is a tissue damage in the dermis and a misalignment of collagen structure caused by various factors such as skin tissue damage, where the body’s organism cannot completely repair the dermis and subcutaneous tissue. According to the definition of scars, what categories can we broadly classify scars into? 1. Proliferative scars Proliferative scars always show protruding surface, irregular shape, uneven height, redness and congestion, solid and tough texture. In the early stage, the local swelling becomes hard and congested, and its tissue structure is a superficial layer covered by a layer of atrophied epithelial cells, a middle layer with dilated blood vessels and infiltration of inflammatory cells, and an underlying layer with fewer collagen fibers and a large amount of connective tissue proliferation. 2. Depressed scars are mainly due to acne, infection, trauma, surgery and other causes of skin dermal layer defects. Insect-like and icepick-like depression scars can be seen after heavier acne, and pockmark-like depression scars can be seen after smallpox and chickenpox. 3. Atrophic scarring is mainly due to acne, infection, trauma, surgery and other causes of skin dermal layer defects. Insect-like and ice pick-like scars can be seen after heavy acne, and pockmark-like scars can be seen after smallpox and chickenpox. 4. Superficial scar Superficial scar is a superficial stable mature scar with rougher appearance than normal skin, flatter, softer texture, and may be accompanied by pigmentation changes. It is mostly seen in mild skin abrasions, superficial skin infections or superficial second-degree burns, and the trauma usually involves only the epidermis or superficial dermis.