The Price of Experience
A few adventurers have scars. These tend to be the result of dramatic events during the character’s backstory. After that, no matter how violent and grievous the injury, it doesn’t scar. Critically hit by a falchion, dumped in acid, caught in a lightning bolt, or smote by divine fire: it doesn’t matter, it won’t leave a mark. Even subscribing to the theory that hit points equal luck, energy, and fatigue rather than physical injuries and that only the blow that knocks you down is a real hit, most characters should have been seriously injured a half-dozen times before they reach level ten. Fighters should resemble Oliver Queen from Arrow, with a body covered in scar tissue.
Also, broken bones and sprained muscles don’t ache when rapid weather changes occur… unless you’re in D&D, where your bones never get broken as the result of a powerful blow!
“As long as I’ve got 1 HP left, I can still take down an army by myself!”
If you think facial scars lowers Charisma, look up “Jason Momoa.” ;)
I know what you’re getting with the hit point/injury thing, but as for injury/CHA-loss, appearance plays a small part of Charisma.
With hit point/injury, I usually rule that if PCs are knocked-down to low or (more over) negative HP by a high-damage attack (as per level) than the character would get an injury that would warrant scarring. I rule that magic healing could remove scarring and other superficial injuries, but this is a rare thing with the genres I run. I have seen other rules handle it differently, like the “Bloodied” rule in the 4e rules.
I always back-and-forth over if magical healing completely restored and negates the injury, or if it acts akin to natural healing only faster, and thus leaves a scar.
But in 5e, magical healing usually just gets people back in the fight and doesn’t completely heal them, and Hit Dice are used to top off restoration. So it might be easier to justify a nasty scar.