The scar heals and the pain is forgotten, but why does a scar remain after the wound heals?

I believe that everyone who has watched "Harry Potter" has fantasized about entering Hogwarts and having a handsome scar and mysterious magical powers like Harry.

Image source: Official stills from Harry Potter and the Sorcerer's Stone

However, the reality is: staying up late and eating hotpot may feel good for a while, but acne will leave scars that will lead to death .

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However, in real life, some people do not easily leave scars even if they are injured. So why do acne marks or scars appear on people's skin? Why do some people rarely leave scars?

Scars that appear to repair wounds

Scars are usually formed when the skin soft tissue is damaged and repaired automatically . But since it has been repaired, why are there still traces left? This is because the skin tissue formed after repair is different from normal skin.

Now let's look at the difference between the two under a microscope. Under a microscope, you can see that there are many cells with different functions in healthy human skin. These loose cells are tightly tied together by collagen like ropes to form a tight skin tissue, which also allows the cells to transmit the necessary nutrients and information. When the skin is injured, these ropes connecting the cells are broken, forming a wound.

The blue lines represent collagen and the cracks represent wounds. Image credit: Ted

At this time, in order to heal the skin, fibroblasts will form many new ropes, namely collagen, at the wound, which is where the rope is broken. They will try to connect the broken parts .

Although wounds can be healed in this way, the arrangement of collagen in healthy skin is often regular and complex, while the repaired collagen can only be arranged in a simple one-way direction . This causes the newly formed skin to be less elastic and sensitive than before. The low elasticity of the repaired skin also causes it to look different from normal skin, which is what we see as scars.

What's worse is that the wound repair may be too strong, producing excessive collagen . This excess collagen will affect the normal functions of the skin, such as sweating and growing hair, and even cause skin hyperplasia and protrusions, making the scar look more obvious.

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Why do some people not easily get scars?

Scars are actually the result of biological evolution . Invertebrates such as octopuses and snails can repair the damage as it was when they were injured, while vertebrates have evolved scars to repair wounds faster. Scars, which seem very hateful to us, are of great significance to animals living in the wild, because scars can quickly close wounds, thereby reducing the rate of inflammation and improving survival.

This evolution is also reflected in human embryonic development. After being injured, the early human embryo can be completely repaired as it was, and scars gradually appear in the subsequent development process. The process of embryonic development reproduces the process of biological evolution, which also indirectly shows that scar repair is a product of evolution.

Since the intensity of scar repair activation varies from person to person , some people are more likely to get scars while others are less likely to do so, and these traits can also be passed on to the next generation. For example, there are obvious differences between different races, with blacks and yellows being more likely to get scars than whites.

Scar formation is also different for people of different ages . Studies have shown that the elderly are more likely to develop scars than young adults. This is because the inflammation and cytokines that cause scar repair in the elderly are very similar to the expression levels of early human embryos.

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Even in different parts of our own bodies, scar formation varies . Wounds in the deltoid and sternum areas are more likely to leave scars, while wounds in the mouth are most likely to heal completely without leaving a scar. Scientists are also studying the different mechanisms of scar formation to help us develop drugs that can inhibit scar formation.

Types of scars left by different wounds

It will also be different

Scars can be divided into many types according to their shapes. The most common type is acne pits, which are called atrophic scars . They are mainly caused by small wounds and not enough collagen is produced during repair, resulting in depressions.

Small wounds caused by minor surgeries are prone to produce small, whitish stretch scars, and stretch marks and obesity marks are also stretch scars. This type of scar mainly comes from wounds deep in the skin: the outermost skin is quickly repaired without damage, while the deeper skin is pulled out of the wound due to excessive tension caused by obesity and pregnancy .

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Normal scars will gradually get smaller within two to three years, but there is another type of scar that will get bigger over time . This scar starts as a small raised scar and eventually grows into a crab-like redness and swelling, so it is called a keloid . The reason for this is that after the wound is repaired, fibroblasts continue to secrete collagen for repair, causing the proliferation to grow larger and larger. This type of hyperplastic tissue is produced by fibroblasts secreting collagen, so it is also called fibrosis .

Everyone must have heard of the word fibrosis, such as pulmonary fibrosis, cardiac fibrosis and other diseases. The causes of these diseases are similar to scars, that is, in order to repair the wounds in the organs, the organs will secrete collagen, and the resulting fibrotic scars will make the organs less elastic like skin , and eventually lead to a series of problems in the organs. So don't underestimate small scars, they may cause big problems!

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Various therapeutic drugs on the market

Is it effective?

For those who pursue beauty, various scar treatment drugs have become their gospel. Common scar treatment drugs contain onion extracts, vitamin E, silicone and other ingredients, or eliminate scars through scar massage, elastic tape, etc. At present, there are studies on the efficacy of various drugs. In the study, different drugs were applied on the scars and compared with the control group that applied vaseline ointment or no treatment to observe the efficacy of each drug.

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Onion extracts were first used to treat scars because scientists found that they could inhibit the production of collagen by fibroblasts in vitro, thus presumably reducing scars caused by collagen. However, in actual experiments, researchers found that there was no significant difference in scars between the onion extract ointment and the vaseline control group, and some patients even had allergic reactions to the wounds due to the stimulation of onions .

Similar to onion extract, vitamin E is believed to have cosmetic effects and can inhibit inflammation and thus inhibit scar formation. However, in actual experiments, it showed no significant effect, either in terms of appearance or Doppler imaging experiments .

Silicone is used to treat scars, mainly because it is soft and rich in water, and is believed to soften the surrounding skin, providing a good environment for the wound to grow more cells instead of collagen. In actual experiments, after 4-6 months of follow-up, it was indeed found that patients using silicone drugs had a slight improvement in pigmentation and size compared with the control group . However, several patients experienced rashes as a side effect during use, and the rashes disappeared after stopping the medication.

Scar tape is used as a treatment because it can make the wound feel normal tension through the connection of the tape, so that there will not be many scar repair reactions. In actual experiments, the effect of scar tape is also very good, and most users recover better than the control group.

Scar massage is based on the fact that massage can break up newly grown collagen, thereby increasing skin flexibility and helping recovery. In actual follow-up tests, it is recommended that patients massage the wound for 10 minutes every day 10-14 days after the stitches are removed, if the skin is completely healed, and the final effect is significantly better than that of the control group.

In short, scars are actually a protective mechanism for us, but if you think they are ugly, you can follow the doctor's instructions for treatment, and never take medication on your own . Finally, I wish everyone can be free of wounds and stay away from scars.

References:

[1]Bayat, A. (2003). Skin scarring. BMJ, 326(7380), 88–92. https://doi.org/10.1136/bmj.326.7380.88

[2]Grigoryan, KV, & Kampp, JT (2020). Summary and evidence grading of over‐the‐counter scar treatments. International Journal of Dermatology, 59(9), 1136–1143. https://doi.org/10.1111/ijd.15060

[3]Sinha, S. (2015). How do scars form? TED-Ed. https://ed.ted.com/lessons/how-do-scars-form-sarthak-sinha

Produced by | Science Popularization China

Author: Earth Story

Producer｜China Science Expo

Submitted by: Computer Information Network Center, Chinese Academy of Sciences

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