How do scars happen?

[Red Earth]

I know they happen for untreated or poorly treated injuries, but I don't know how exactly treating and healing work.
So, healing happens over time. Is there a time limit on how long it can heal, tending determines the heal rate, and unhealed health at the end of the limit becomes a scar?
Or, tend quality determines how much hp can be healed and if the damage is more than can be healed, it remains as a scar?
Or is there another explanation?

[HunterSilver]

From my understanding, any time you take damage on fleshy bits there is a chance for them to immediately become a scar (mangled eyes, brain damage, etc.) and after that the game periodically checks if an injury becomes a scar while it's healing based on room cleanliness and how well the injury was treated.

So untreated injuries in rooms covered in blood, vomit, and dirt are very likely to develop infections and scars. Injuries with 100% treatment in sterile hospital rooms basically never get infected or scar.

I don't know any actual formulas for this, but this is what I remember from my own experiences.

[martindirt]

We should summon Astasia.
She has a deep knowledge how the code works and knows numbers what I don't know where she finds.

[UltimateTobi]

I summon thee, Astasia.
Shall your knowledge enlighten the OP's path.

[Harry_Robinson1]

Originally posted by HunterSilver:

From my understanding, any time you take damage on fleshy bits there is a chance for them to immediately become a scar (mangled eyes, brain damage, etc.) and after that the game periodically checks if an injury becomes a scar while it's healing based on room cleanliness and how well the injury was treated.

So untreated injuries in rooms covered in blood, vomit, and dirt are very likely to develop infections and scars. Injuries with 100% treatment in sterile hospital rooms basically never get infected or scar.

I don't know any actual formulas for this, but this is what I remember from my own experiences.

This is correct from my experience and all the research I've done but I also summon Astasia

[Astasia]

I don't actually have solid info here. This mechanic isn't defined in the XML (AFAIK) and the little info that can be found out there is often conflicting. At one point at least I know there was a check to turn an existing injury into a scar based on tend quality, I think it was basically anything over 10% tend quality more or less removed the chance for it to scar (or the chance was astronomically low), while tend quality under 10% still had a very low chance to scar but could realistically happen. I've also heard that mechanic never worked, and whether a wound scars or not is only decided when the damage is taken and tending the wound has no effect on the chance.

In my experience, scars on normal bodyparts are so incredibly rare that I can't really tell if there is any pattern. You want to tend quickly in a sterile environment with a good tend chance to avoid infection and speed up healing anyway, and if the wound scaring mechanic works then that pretty much eliminates the risk of that happening. Maybe if you don't tend a bunch of injuries, or get 0% tends, you will start seeing more scars? That's not really something anyone would normally do though. I imagine that's why there isn't a lot of information out there on it.

[Steelfleece]

From personal experience where I usually tend to raiders' injuries with lower-skilled colonists and often with no medicine (need to raise their skills enough so they can patch wounds in emergencies after all, but I don't want to spend a lot to do so), scars do seem to trend with lower tend qualities. When I'm seeing lots of 0% and similar tends, every second or third raider winds up with at least one cool scar to show off back home. Using higher quality tends on colonists, scars seem exceedingly rare.

I mean, aside from eyes and brains, pretty much any damage to those is an instant scar.

[Cannenses]

Originally posted by Steelfleece:

... eyes and brains, pretty much any damage to those is an instant scar.

For these internal organs -- eyes, brain, lungs, etc. -- I believe Glitterworld medicine on pawns (maybe even animals) will heal without scars. It worked out in a self-tend situation, who had an eye injury (eyesight matters for medic skill) after a melee fight in my case.

Also, this pawn has 'Superfast wound healing' gene. This might have helped.

[HunterSilver]

Originally posted by Cannenses:

For these internal organs -- eyes, brain, lungs, etc. -- I believe Glitterworld medicine on pawns (maybe even animals) will heal without scars. It worked out in a self-tend situation, who had an eye injury (eyesight matters for medic skill) after a melee fight in my case.

Also, this pawn has 'Superfast wound healing' gene. This might have helped.

These body parts seem to be very likely to scar immediately upon taking damage. You can test and verify this on larger animals like Thrumbos very easily, where after just a few seconds of receiving a volley of fire, they'll have lots of permanent scars on body parts like their eyes and brains. This means you won't even have a chance to tend before a scar occurs. When they don't scar immediately, they can be tended and healed like normal though.

[The Blind One]

some body parts have a built in scar chance multiplier

Example;

  <BodyPartDef>
    <defName>Eye</defName>
    <permanentInjuryChanceFactor>15</permanentInjuryChanceFactor>

This effect seems to only apply to the eyes (15x), the spine (6x) and the brain (over 9000x) more at risk of becoming scarred.

Many body parts also have a 0x factor meaning that they are impossible to become scarred. (noses, jaws, ribcages, arm and leg bones)

[Jaasrg]

Had a scrub termite shoot at my tribal and BAM, instant heart scar.

[martindirt]

Originally posted by The Blind One:

some body parts have a built in scar chance multiplier

Example;

  <BodyPartDef>
    <defName>Eye</defName>
    <permanentInjuryChanceFactor>15</permanentInjuryChanceFactor>

This effect seems to only apply to the eyes (15x), the spine (6x) and the brain (over 9000x) more at risk of becoming scarred.

Many body parts also have a 0x factor meaning that they are impossible to become scarred. (noses, jaws, ribcages, arm and leg bones)

This is why you don't want your pawn to fight in bowler hat. Put at least a pot on the heads.

[The Blind One]

looking a bit deeper into the source code,

take it with a grain of salt and not as gospel since I barely know how code works but;

there's a 2% chance of scarring by default which is multiplied by the permanent injury chance factor (6x for the eye for example) as I previously showed and how severe the injury is ranging from 0 to 1 (with 1 being completely destroyed, though, you won't get a scar in that case lol)

Effectively it means that if a body part is only damaged by 20% of its max HP the chance of a scar is also only (20% x default 2%) just 0.4%

(this seems to be applied every time a body part gets injured, which makes sense. So there's a strict theoretical max ~2% chance of scarring when a body part is reduced to 1hp no matter how many injuries it sustained on the way there, though you can get a scar with every injury sustained, theoretically)

There's also some other stuff that I couldn't figure out which is probably related to how well treated a wound is but I can't be sure on that.

From what I can tell, scarring happens when an injury takes place, not when it is treated. So treatment possibly has no effect on scarring but I could be entirely mistaken on this. Someone with better code knowledge should come in and explain it honestly lol