Where does Koloss skin come from?

[amflare]

As Koloss grow, their skin goes from super loose to stretching and breaking.

Quote

It was a creature of smaller size—perhaps six feet tall. It was man-shaped, with two arms and legs, though its neck was hard to distinguish. It was completely bald. The oddest feature, however, was its blue skin, which hung loose and folded.

[...]

Like... a person wearing a mask made of skin, Sazed thought, trying to push away his disgust. So... their body continues to grow, but their skin doesn't?

His thought was confirmed as a massive, ten-foot-tall beast of a koloss wandered into the group. Smaller creatures scattered before this newcomer, who thumped up to the fire, where several horses were roasting.

This largest creature's skin was pulled so tight it was beginning to tear. The hairless blue flesh had ripped around the eyes, at the edges of the mouth, and around the massive chest muscles. Sazed could see little trails of red blood dripping from the rips. Even where the skin wasn't torn, it was pulled taut—the nose and ears were so flat they were almost indistinguishable from the flesh around them.
_{Well of Ascension - Chapter 19}

 

 

They are also fairly violent creatures who fight a lot. Which, of course, damages the skin more.

Quote

One of the koloss beside Sazed howled in sudden anger. Sazed spun as the koloss jumped at one of its companions. The creature ignored the sword on its back, instead punching his enemy's head with a blocky fist. The others paused, turning to watch the fight, but none of them seemed alarmed.

Sazed watched with growing horror as the aggressor proceeded to repeatedly pummel his enemy. The defender tried to protect himself, getting out a dagger and managing to score a cut on the aggressor's arm. The blue skin tore, seeping bright red blood, as the aggressor got his hands around his opponent's thick head and twisted.
_{Well of Ascension - Chapter 19}

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But Koloss also reuse the skin when creating new Koloss.

Quote

Vin rushed ahead, cutting him off just as he reached the tent with the wounded. "Human," she said warily. "What are you doing?"

He ignored her, slamming the dead koloss down on the ground. Now, finally, Human ripped the skin off the corpse. It came off easily—this was one of the smaller koloss, whose skin hung in folds, far too large for its body.

Human pulled the skin free, causing several of the watching guards to groan in disgust.

[...]

A spike. A small metal spike driven into the side of the dead koloss. There was a rip of blue skin beside the spikehead, as if...

As if the spikes were holding the skin in place, Vin thought. Like nails holding cloth to a wall.
_{The Hero of Ages - Chapter 37}

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^{(all bolded emphasise mine)}

So if the skin is reused, but also extremely prone to damage, where does new skin come from when they need to replace one? Over here, someone postulates that it is the skin of the "host" human, but I'm not convinced.

Edited September 27, 2018 by amflare

[MountainKing]

It's the skin of the host human. Human wanted the spike in the skin, not the actual skin.

[Ashertliden]

When Koloss harvest from the bodies of dead Koloss, they do not reuse the skin of the Koloss, they simply reuse the spikes. The skin, I believe, grows from the host human from the areas the spikes are implanted soon after the spiking is completed. 

Edited September 27, 2018 by Kal-Eldin

[+Invocation]

90% sure that them taking the skin off was to either make sure they had all the spikes gone or a death ritual.

[Yata he/him]

The Skin isn't required at all, simply Human ripping off the Spikes ripped also some skin that as you pointed in the OP isn't really too strongly attached to the Koloss