Scarred tissue occurs when tissue is damaged and an inflammation response occurs in the body. Acne scars are caused when the pimple or pustule is ruptured and forces the clogged pore to open, harming the tissue. The tissue gets red and inflamed, and in healing can either form melanin or an overgrowth of tissue to help protect the damaged skin.
Another type of scarred skin is stretch marks. Stretch marks are caused when the dermis is rapidly stretched and the tissue is torn. The natural inflammation response happens making the tissue red and swollen. The epidermis is also opened and becomes translucent, making it able to see the striae if damaged skin tissue. After some time, the damaged tissue will become scar tissue and usually turns a white milky color. The scars are usually indented parts of the skin because they have virtually no collagen or elastin fibers to support the layers of tissue.