system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can't we use all the excess skin from people with extreme weight loss to treat burn victims?

With the technology surrounding grafting, why can't we take the huge amounts of skin that come from the formally obese and graft them to victims that have suffered severe burns? If skin 'typing' is an issue, it seems we could setup a global exchange - there is demand on both ends it would seem?
gpt
Your cells have specific proteins on their membranes that serve as markers for your immune system to differentiate self from non-self. These proteins can vary from person to person, although they serve the same function.

The reason you typically graft skin from yourself is that the skin will not be rejected by your immune system, where as if you used someone else's there's a very likely chance it will be rejected and cause an immune response.