Scar healing which heals with a scar. The myofibroblasts make up a high proportion of the fibroblasts proliferating in the postembryonic wound at the onset of healing. In the rat model, for instance, myofibroblasts can constitute up to 70% of the fibroblasts, and is responsible for fibrosis on tissue. Generally, the myofibroblasts disappear from the wound within 30 days, but can stay around in pathological cases in hypertrophy, such as keloids. Myofibroblasts have plasticity and in mice can be transformed into fat cells, instead of scar tissue, via the regeneration of hair follicles. Early and effective treatment of acne scarring can
Scar or muscle, are lost. This type of scarring is often associated with acne, chickenpox, other diseases (especially "Staphylococcus" infection), surgery, certain insect and spider bites, or accidents. It can also be caused by a genetic connective tissue disorder, such as Ehlers–Danlos syndrome. Stretch marks (technically called "striae") are also a form of scarring. These are caused when the skin is stretched rapidly (for instance during pregnancy,<ref name="doi10.1002/14651858.CD000066"></ref> significant weight gain, or adolescent growth spurts), or when skin is put under tension during the healing process, (usually near joints). This type of scar usually improves in appearance after a few years.