Eli5 why do stich marks and some wounds never fully go away?

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I have stitches on my finger and my lip along with a scar on the back of my left thumb, and several marks on my arms, all have been there for several years, why do they never fully go away?

In: Biology

Think of your body as a house with an absent-minded homeowner who does do-it-yourself repairs. One day, the neighborhood kids hit a baseball directly through the front window, smashing one of the panels. The absent-minded homeowner never saved blueprints for the house or took pictures of it. For this damage the owner could figure out that the broken part was inside window and all they need is to patch it up and get some replacement glass. In this case, the wound on the house could be fully regenerated so the house looks the same afterwards.

On another day, a drunk driver crashes their car through the front of the house, taking out the window and its frame entirely. Now, the first thing to do is to make sure the wound is sealed. You don’t want things from inside the house from leaving and you don’t want the outside critters or weather to come in. The homeowner throws everything they can to seal it but it’s not enough. The homeowner has to call the specialists (doctors) to help seal the damage.

The specialists have to add additional holes (wounds from sutures) to the house and pull it together (stitches) to help seal the house. This pulls the walls together so the overall wound is smaller and easier to seal by the homeowner.

Remember that the homeowner doesn’t have good memory or blueprints for the house. With the window knocked out, the homeowner doesn’t realize they have to add one. The body only knows how to heal based on the healthy tissue around it. With the walls stretched together, it doesn’t resemble any regular wall they’re used to fixing. Better to just plaster it over and hope it’s sealed.

This is known as a scar. Scars form over wounds where the body doesn’t know how to properly regenerate. They lack the normal functions of the tissue. For example, scarred skin doesn’t have hair or sweat glands. Over time, the fibers in the scar will tighten, pulling the wound closed and reducing the appearance of the scar but some may remain in place forever.