Today, we'll look at an interesting issue raised by one of Harry's trademarks: his scar. What makes a scar form, and why do some people form more distinct scars than others? If Neville had indeed been Voldemort's victim that night (we've already discussed the ambiguity in the prophecy that had the evil wizard so freaked out), would he have the lightning bolt mark on his forehead, or was it something specific about Harry that allowed the now infamous badge of courage to form?
First of all, the basics of wounds and healing. When you sustain a wound like a laceration of the skin, the first thing the body does is send up an inflammatory response. A whole squad of chemicals and cells are sent to the rescue: leukocytes and monocytes to combat bacterial infection, fibrinogen to help join the edges of the wound together again, and blood platelets to form clots (hemostasis = stop the bleeding, see a cool animation here). It is thought that if you're on any anti-inflammatory drugs or steroids, this can prolong wound healing because it decreases the initial inflammatory response to the tissue damage.Next, fibroblasts come in to start synthesizing collagen, one of the body's essential connective tissues. This is where the difference between simple wound healing and scar formation comes into play. Basically a scar is just what happens when an excessive amount of collagen is produced to repair a wound. When most people think of severe scars, they pictur
e what are known as keloid scars, defined as "an abnormal scar that grows beyond the boundary of the original site of a skin injury," and "dermal fibrotic lesions." Interestingly, some areas of the body are much more likely to form keloids than others: knees, deltoids, and the upper back and sternum. These are all areas of high stretching and tension on the skin and muscles, which could be a factor.
There is actually a medical distinction between "hypertropic" and "keloid" scars: keloid scars extend beyond the boundary of the original injury, they basically color outside the lines. Nevertheless, the terms tend to be used fairly interchangeably, there can sometimes be a fine line and difficulty determining the boundaries of the original wound, especially in trauma cases. Googling for pictures of each kind, the results tended to look pretty much the same.
You can reduce the chances of forming this type of scar by using a pressure dressing, but there seems to be a strong genetic component involved in the susceptibility to keloids. People with Type A blood tend to form them more frequently than other groups, and there are also racial trends. African-Americans and Hispanics are 16% more likely to keloid than Caucasians, and other ethnic groups classified as "highly pigmented" are 15 times more likely to form them as well.
Why are some people/groups more likely to develop keloids? As you probably guessed from the racial patterns, it is related to the darkness of the skin. The shade of your complexion is determined by the concentration of melanocytes in the skin. Just like pointillist paintings create the illusion of darkness by concentrating uniform-sized points into clumps, higher concentrations of meloncytes give you darker skin. (In some black fraternities branding the skin is used as an initiation instead of tatoos, since it is much more distinctive on dark skin). This creates the potential for more severe pigment disturbances after a trauma, and many times the scar tissue is lighter than the surrounding skin because the collegen doesn't have the same melanocyte levels as the original integument. This also makes laser removal of scars more difficult for dark-skinned people, because melanin has a wide absorption spectrum and intercepts the laser energy intended for hemoglobin cells.
As you saw from the statistics, though, not all keloid-formers are black, many Caucasians form them too (personally, I am horribly prone to keloids, I even get them from minor nicks and scratches that barely even drew blood in the first place). This tendency is genetic: you're much more likely to form these scars if you have a parent that does (my dad does, mother doesn't, damn that paternal allele). There have been cases reported that indicate either autosomal dominant or autosomal recessive inheritance, so there is currently no consensus on transmission patterns, although HLA-B14, HLA-B21, HLA-BW16, HLA-BW35, HLA-DR5, and HLA-DQW3 are considered to be risk factors.
This study claims that "abnormal wound healing is unique to humans," I'm not sure where they got that idea, because I worked in the research kennels a vet school last summer and saw many dogs with horrific networks of scars from various experimental procedures.
So, what does this tell us about Harry? Not a whole lot, actually, as interesting as it all is, we don't have the data to draw many conclusions. His mother and/or father probably carried the genes associated with excessive collagen synthesis. The most interesting question about the issue, to me, is wondering whether Neville would have formed the same scar if it had been him under the Avada Kedavra curse that night. We can't know, without knowing what his genetic susceptibility is.
It may not be genetics in this case, however. In other cases of Avada Kedavra killings that we have seen, the spell creates an explosion upon impact, and if there is anything around to catch fire (clothing, etc), it goes up in greenish flames. This definitely doesn't explain the neat little zigzag pattern that Harry sports. No one else that has been hit by the curse has formed this, but then again no one has ever survived it, either, indicating that it could truly be something intrinsic to Harry that created the trademark.
For a long time, Rowlings said that the last word of the last book would be "scar." After ten years, though, she recently announced that she may have changed her mind. I'd be interested to know why, obviously when you start a decade long writing project many things won't turn out the way you planned, but after she had created so much hype about that one fact I would really like to know what caused her to change her mind. I, however, am waiting to read the book myself, still fuming about spoilers and pirated pictures zinging around the internet...
Just as a side note, the scar has always been a major point of annoyance for me in the movie versions of the series. They portray it as a large scar, kind of high and to the side, while I always pictured it as being more centered and lower, more like what is shown in the book illustrations:
This is the last Harry Potter Science post before the book release tomorrow, but I do have some ideas that I didn't get to cover yet (I should have started more than a week in advance, I guess), so there will be a few more additions to the series in the future, if all goes as planned, and hopefully the last book will provide even more material, I've had a lot of fun doing this!
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