When I was 10 or 11 years old, I hurt my knee at summer camp when I fell running around a gravel-covered walkway with some of my bunkmates. I fell hard enough that a few tiny pieces of gravel actually embedded themselves under the skin that covered my kneecap.

In the infirmary, after the nurses wiped away the blood and washed the gravel bits out of the skin, they placed a bucket under my leg and poured rubbing alcohol over it. It hurt, but at least I didn't get an infection. What I did get, however, was a nice scar. Then there was the time I stabbed my hand with a knife while attempting to open boxes in my college dorm room. Despite my best efforts, that, too, resulted in a scar on my left hand, in the space between my thumb and first finger.

Nearly everyone has a good scar story (or two, or three) they can tell in an effort to one-up their friends' stories. But what exactly is scar tissue anyway?

For one thing, a scar is a virtual certainty following a wound of any sort, at least to some degree. That's because a scar is the natural outcome of the body's normal healing process as it works to repair the skin or another of its organs. However, animals that regenerate parts of their bodies, like limbs or tails, can do this without scarring.

After a wound, burn, or injury, the first thing the body does is bleed. The second thing the body does is form a blood clot. The very top layers of the clot dry out and harden to form a scab, which protects the wound from additional disturbances. Protected from the external world, the lower portion of the clot becomes host to cells called fibroblasts, whose job in part is to replace the scab with scar tissue.

Rather than slowly build skin the usual way, scars are the work of the body's rapid response team  

But while the tissue that makes up a scar is made of the same stuff as normal skin – a protein called collagen, primarily – it looks and feels different. In a 1998 paper in the Bulletin of Mathematical Biology, University of Warwick mathematicians John C Dallon and Jonathan A Sherratt explained why. "In humans and other tight-skinned animals," they wrote, "collagen has a cross-weave structure in normal tissue, whereas in scar tissue it is aligned parallel to the plane of the skin."

In other words, normal skin tissue is constructed of fibres that are oriented randomly to each other, while the very same fibres, in scar tissue, are oriented in a single direction, parallel to each other.

It's actually quite reasonable, from an evolutionary perspective. An open wound leaves the body susceptible to all sorts of problems, from intense pain to infection. So rather than slowly build skin the usual way, scars are the work of the body's rapid response team.

Think of it this way – if you've got a hole in your roof and it's raining, it's not worth waiting for the best carpenter in town if the second-best carpenter is available. Especially if he can get the job done in half the time for half the price. It's better to protect the body from the outside world as soon as possible, even if the handiwork is a bit sloppy.

While some scars are a source of pride, others might be aesthetically displeasing. And though there aren't any methods to completely avoid scarring, there are ways to minimise their formation or appearance. For one thing, larger wounds mean larger scars. That's why doctors so often use stitches. Reducing the amount of space between the two ends of a wound results in a smaller scab, and therefore a smaller scar.

If a scar is particularly unsightly, a dermatologist might recommend "revising" the scar. In this process, the scar is entirely removed and the skin is re-stitched. Because scars are unavoidable, a new one will form, but the doctor can work to make it less obvious.

Only a skin graft can completely remove a scar, and even then a new scar will appear along the edges of the graft  

Other forms of treatment, like chemical peels or dermabrasion work by removing the outermost layers of skin. The skin then heals from this kind of controlled assault, and as a result the newer, younger skin could appear more uniform.

But while each of these methods may result in an improved appearance for some folks under some conditions, none of them actually remove scars entirely. They only alter them, adjust them, relocate them, or otherwise increase their acceptability.

Only a skin graft can completely remove a scar, and even then a new scar will appear along the edges of the graft. So until medical science comes up with something better, the majority of us will simply have to remain content with trading scar stories.

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