system
Given the following post, respond as if you're commenting on Reddit:
human
How does keratin in human differ from keratin in other animals?

I know that keratin is what makes up skin cells and hair cells, and that animals with shells and tougher skin are also made of keratin. My question is, how are they different? Is it to do with the thickness? Are there other proteins involved that makes it stronger/weaker? What determines it's color and texture?
gpt
Keratins in animals are not fundamentally different that keratins in humans.   
The hardness of keratins is mainly determined by the sulfur content. Harder keratins, like hooves, have a higher sulfur content. The reason why is somewhat complicated, but basically the sulfur allows parts of the protein to stick to other parts of the protein, making it more rigid.