If they say that all human cells replace themselves every 7 years or so, why can scars remain on your body for the entire life?

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If they say that all human cells replace themselves every 7 years or so, why can scars remain on your body for the entire life?

In:

Because scars formed not only by cells, but also by fibrosis tissue, which is mostly formed by proteins between cells. Also, 7 years cycle is myth. Some cells live for days (like sperm), some for weeks (external layers of skin), some for months (red blood cells), some – for an entire life (neurons).

because scar tissue is not the same *type* of tissue as surrounding tissue. So even if the scar tissue is replaced, it’s replaced with the tissue making it up, which does not look the same as the other tissue around it.

For example if you get a small cut the tissue on either side of the cut divides and meets in the middle to repair the cut.

With a larger cut, it might take too long to do this – we need it closed ASAP. So you have tissue from the sides coming together but *also* tissue coming up from below in the middle and all three meet. But now the middle looks like the “below” tissue because that’s what it’s made from

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Unfortunately that piece of information is wrong. All human cells do not replace themselves every 7 years, otherwise we won’t have diseases like Alzheimer’s which are caused by neurons getting damaged over time. Some cell types can replace themselves, such as skin, some can’t, like neurons.

Specific to scarring, the cells that heal the damaged area are not skin, but rather from fibrous tissue. Because of this, even after the scar heals, it remains that way, and future injuries and healings to the scar may also not make it go away.

Ref: https://en.m.wikipedia.org/wiki/Scar

Edit: replaced neurodegenerative with “neurons getting damaged over time” to make it Eli5 compatible

Edit 2: broke the single sentence second paragraph into two sentences for readability

scar tissue is shaped differently on a microscopic level that the rest of your skin. it replaces in roughly the same shape but the edges do shrink over time as more and more of the tissue corrects itself with each iteration, its just hard to notice because it takes such a considerable amount of time. i used to have 4 thick meaty scars down my back from when i was lil but they dont exist anymore

Imagine the body like a building.

The connective tissue (collagen mostly) = [steel skeleton](https://www.dreamstime.com/steel-skeleton-tall-building-under-construction-crane-tower-steel-skeleton-tall-building-under-construction-crane-image123978264)
The human cells = the bricks, windows, doors, everything in between.

A scar is usually a damage to this steel skeleton not the bricks/walls because they can always be changed.

Which cells are never replaced, and are as old as we are?

What exactly is a scar and why doesn’t the body just use normal skin instead of scar tissue to repair cuts? Is a scar a different kind of skin?

The cells get replaced by being ‘copied’ so when mistakes are made/created they are also copied.

This why/how ageing happens, mistakes in the system of copying and reproducing the cell are retained.

It’s a very complex system so it’s amazing it works properly at all. The minimal mistakes that happen are not surprising.

If it works dont change or modify it.
Body changes scar cells with same scar cells so it remains same.

Interesting…..I had a scar from a deep cut on my left index finger knuckle from when I was like 6 years old and it disappeared by now, i’m 32.

What should trouble you is that you are literally not the same person now as you were 7 years ago 🙂

First of all, human cells don’t replace themselves after 7 years. This idea is false.

We have about 50-75 trillion cells in our bodies, and there’s tons of types, each with their own life-span:

* Red blood cells – 4 months
* White cells – 1 year
* Colon cells – 4 days
* Sperm cells – 2-3 days
* Neurons – Our entire lifetime

Cells aren’t all the same age. They die and are replaced all the time, in a continual process.

There’s also the matter that scars are the consequence of open wounds. An open wound triggers a quick reaction during which the body tries to seal off the entry to prevent infection as soon as possible. That’s the most important matter, and not aesthetics.

With a larger wound, once the “crust” is formed (which is basically layers upon layers of dead cells), skin cells start filling in the gap. Some of them start on the edges of the cut, and as such will connect quite well to the unharmed cells. But part of them come up from the middle and underneath the scar, forming basically a new “batch” of skin.

The gaps need to be bridged and the imperfect connections between the edge and middle replacement skin are how scars show up.

It is 10 years, and scars do go away.

The only scar I have left is from a deep puncture wound I recieved on my left forearm just below the elbow, and as thick as it was it is almost gone.

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Scar tissue is mostly emergency scaffolding that’s put into place as a quick fix. It isnt made of cells, though it is slowly replaced by living cells.

Thing is, the stuff that breaks down scar tissue to allow normal cells to come and replace them can’t get to it all of the scar is dense enough. So big scars will last a long time because of this.

That’s why a lot of the time doctors will tell you you gotta stretch muscles that have been worked on in surgery after they have healed, even if it hurts. Their are also tools for breaking down scar tissue on the skin.

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