This list is of MPs who have burn scars, not ordinary ones, but serious scarring covering a sizable area of skin. What counts as “sizable” is entirely up to me. For what it’s worth, I’ve heard they recommend you seek immediate medical attention if you’re burned over an area larger than your hand. In some cases I’m not 100% sure the scarring is really large, but only reasonably sure. Cynthia Milstead being an example of that.
I think that in some cases, burns can cause damage that will be apparent in the skeletal structure as well as the skin. I’d guess they’d have to be quite severe for that to happen, though.