Typically in this scenario you would refer to the procedure as a skin graft, where skin is taken from an area of healthy skin (which will eventually heal) and laid down on another area where skin has been lost.

Skin is an organ that requires blood flow to survive, just like any other organ. When you graft skin, you depend on its ability to "take", that is, to integrate into the bed you've laid it on. This requires growing new blood vessels from the bed into the graft. If it doesn't happen before the graft dies from lack of nutrition, the graft fails.

Graft take relies on the healing process, which among other things involves a lot of cell growth and division. Radiation kills or impairs cells' ability to divide, leading to reduced ability to accept a graft.

I don't know specifically if/why radiation burns would be worse than regular thermal burns in this regard, but my suspicion is that it is due to greater depth of penetration with radiation vs. thermal energy.

Radiation affects the vascular supply (long term not immediately after).

1. Don't skin graft an immediate radiation burn, most heal
2. Long term - may develop ulcer which doesn't heal. Skin graft won't work. Need a vascular pedical flap that has its own blood supply

The phases of STSG healing are imbibition (drinking) where the graft is fed by absorbing plasma that comes from the recipient, inosculation (kissing) where the new tiny blood vessels of the graft start to touch new blood vessels in the recipient, and finally neovascularization where the blood vessels mature between graft and recipient.

The radiation destroys small blood vessels so irradiated tissue fibroses, has poor oxygenation and therefore has low oxygen tension in the plasma secreted and cannot go through the inosculation phase.

This is also true of full thickness thermal or chemical burns which is why you have to excise to vascularized tissue prior to grafting.

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