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Harvard Commentaries
Harvard Commentaries
Reviewed by the Faculty of Harvard Medical School

Medical Myths Medical Myths

Leaving a Mark -- How and Why We Scar

January 06, 2015

By Robert H. Shmerling M.D.

Beth Israel Deaconess Medical Center

The way skin heals is a remarkably complicated process. It's amazing how few scars most people have despite a lifetime of injuries to the skin.

If you've had surgery and can barely see the scar, should you thank your surgeon? And, if your scar is large and irregular, does your surgeon deserve the blame?

Scarring may be less related to the skill of your surgeon than you may think. So, what determines how we scar? The answers may surprise you.

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How Scars Develop

When you cut yourself (or a surgeon makes an incision), your body has ways to limit the bleeding and begin wound healing and repair.

There are three processes that take place — in roughly the following order, although often these happen at the same time:

Inflammation – Within seconds of a cut or an incision, chemical messengers are released that tell blood vessels to narrow. This limits bleeding until blood cells (called platelets) can plug up the bleeding and a clot can form. This also helps keep proteins (including those involved in healing) in the tissues.

Other chemical messengers are released (called chemotactic and growth factors) that recruit blood cells and other substances to the injured area. Soon, blood cells release a flood of chemical factors to relax blood vessels and increase blood flow. This causes the pain, redness, heat and swelling typical of inflamed tissue. Immune cells that fight infection and clean up damaged tissue now invade the area.

Proliferation – Cells that form new blood vessels, skin and scar tissue are called into action. Other cells help the clot to dissolve. Slowly, new cells inch their way around the wound to form a protective covering. Skin cells burrow under dead tissue to begin forming a healthy layer of skin. Fibroblasts, specialized cells that are critical to wound healing, invade wounds to produce collagen and elastin. These are required for healthy skin. The wound actually contracts. The ends move closer to one another due to the action of another set of specialized cells called myofibroblasts.

Maturation – The wound gets stronger. The skin's ability to tolerate pressure peaks 60 days after the injury. But it only reaches 80% of the strength of uninjured skin.

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Why Are Some Scars Bigger Than Others?

If a wound is "clean" — even, straight and at right angles to the skin — it will generally heal well as long as the two sides are brought together. If the two sides are too far apart, sutures (stitches), staples or tape can bring the edges together.

The length of a surgical scar depends on how much room the surgeon needs to perform the surgery. For example, a large tumor that's hard to reach may need a long scar. But a much smaller incision may be just fine for surgery that's easier. Many operations that used to require long incisions can now be done with a "mini-incision" or through a laparoscope (a thin, flexible tube with a light on the end through which a surgeon can see into the abdomen or pelvis).

The final appearance of a wound has less to do with the surgeon's skill or meticulous care than you may think. A thick, raised or jagged scar may be the result of:

  • A jagged wound that varies in depth
  • A thick scar, called a keloid, that some people (especially African-Americans) form in response to injury; the scar tissue extends outside of the wound. Another type, hypertrophic scar, is thickened scar tissue that does not extend beyond the confines of the wound. Both are common among dark-skinned persons. They are probably a genetically programmed response to injury (although the precise mechanism is not clear).
  • Dirt stuck inside the wound so it doesn't heal well. The wound may appear less uniform than a cleaner wound. This type of injury might occur after falling from a motorcycle and suffering a "road burn" injury.
  • Repeated injury or re-opening of a wound
  • Infected wound
  • A gaping wound that needed sutures but did not have proper treatment

Unsightly scars can be repaired. But people who are prone to hypertrophic scars or keloids may need special treatments, such as laser therapy.

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Which Wounds Need Sutures?

In general, a deep wound or one in which the two sides do not naturally fall back together is likely to require sutures. The idea is to bring the two sides back together so that the healed wound will appear much like it did before the injury.

How can you tell if a wound needs sutures? Sometimes, it's obvious. Other times, you'll need a doctor to decide.

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The Bottom Line

Skin is an amazing organ. Even without surgery, most people get enough injuries to the skin to cause scars. So, if you have no scars or ones that are barely noticeable, consider yourself lucky. But you should also give credit to your skin's ability to heal. It's a part of the body that's particularly good at that.

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Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.

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