Scars!

Scar are made up of jumbled bundles of fibrous protein known as collagen, which are laid down in the skin as the body attempts to heal itself after injury. They are caused by injury, rapid body growth, infections and operations and are the body’s way of healing disfigured and injured skin tissue.

Our skin has three main layers:

1. The epidermis, which is the thinnest and outermost layer. It is composed of layers of flattened epithelial cells which act as armour to protect the body from the outside world.
2. The dermis, which is just under the epidermis, is the thickest layer and contains blood vessels, nerves, hair follicles and sweat and oil glands. Within this layer, there is a fibrous network of proteins called collagen and elastin, which support the structure as well as the elasticity of the skin.
3. The hypodermis is under the dermis and is the deepest layer of skin, containing fat tissue to cushion the internal organs and to shield deeper tissue from injury.

If the outermost layer of skin, the epidermis, gets damaged (by events like sunburn) it simply peels off, leaving the deeper layers of skin behind and intact until it eventually regenerates. However, if the dermis gets injured, a scab forms to protect that area and inflammation is caused to start the healing. This healing causes scars to form due to the strange way the body heals skin. In normal skin, the dermis's network of collagen fibers is like a piece of fabric that is carefully woven in a nice, smooth pattern. If an injury tears this fabric, the body makes new collagen fibers to fill in any gaps. However, instead of nicely weaving the new fibers back together across the wound, the body dumps them all together in a jumbled pile. This messy buildup of collagen makes up most scar tissue, making it look different from normal skin as well as making it less flexible than normal skin. These are called hypertrophic scars. Keloid scars are raised and larger than the actual wound because the body lays down more collagen than it has to. These scars are more common amongst dark skinned people, which is probably for genetic reasons. Hypertrophic scars are more common in adolescents and pregnant women due to their heightened hormone levels. 

Scars in light skinned people start out as pink and slowly darken, ending up with a colour that is a little darker than the person’s skin colour. If a dark skinned person gets scarred, the scar looks like a dark spot. One significant difference between scar tissue and normal dermis tissue is that scar tissue does not contain any glands or hair follicles. Scars fade within six to eighteen months as the collagen tissue flattens, but they never fully disappear because their tissue is still very different from the skin tissue around them.

Humans can make scars fully vanish by making the skin completely regenerate, like salamanders. However, humans only have this ability as fetuses and lose this ability after the second trimester of pregnancy. It is not known why this is so. There have been studies where adult skin tissue was transplanted onto a fetus*, but the transplanted tissue still scarred, which indicates that adult skin tissue is ‘programmed’ differently and so always scars. Scientists think this is because the differences in the amount and locations in stem cells, but this research is still in one of its first phases.

*For more information, please research independently. This article does not focus on this topic.

Main Source:

https://www.livescience.com/health/anatomy/why-are-scars-permanent