Scar muscular power and possibly heart failure. However, there are some tissues (e.g. bone) that can heal without any structural or functional deterioration. All scarring is composed of the same collagen as the tissue it has replaced, but the composition of the scar tissue, compared to the normal tissue, is different. Scar tissue also lacks elasticity unlike normal tissue which distributes fiber elasticity. Scars differ in the amounts of collagen overexpressed. Labels have been applied to the differences in overexpression. Two of the most common types are hypertrophic and keloid scarring, both of which experience excessive stiff collagen bundled growth overextending
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.