[rustcleaner]

It's a microwave, non-ionizing. They're pretty much easy-bake ovens which shine a monochromatic light at a color water is very black/absorptive at (a color far redder than infrared). They cook outside-in so he'd be baking his skin well before internal injury.

[HPsquared]

It would be like thermal burns but deeper. The heating is more diffuse and deeper than traditional cooking methods so I'd imagine if you did get a burn, it would go deeper into the tissue than you might expect.

[frabert]

https://www.youtube.com/watch?v=3hBRxwQXmCQ This guy recklessly tested various way of getting irradiated by a microwave to see what the effects are.

[chongli]

An extremely irresponsible video. He talked a lot about scary apocrypha to do with eyeballs exploding but never once mentioned the possibility of vision damage or blindness without the drama. I think he knew that microwaves are extremely dangerous to your eyes and avoided doing the most potentially damaging things without talking about it. To whit:

If you bypass the door interlocks and operate the magnetron with the door open and then stick your head into the cavity, you risk have your eyes pass through one of the microwave peaks in the standing wave pattern set up by the cavity. Extremely intense, localized heating within your eyeballs is never a good idea, and you risk burning your retinas or damaging your corneas or lenses.

The eyeball is large made of water and protrudes somewhat from the eye socket. Peering forward into the interior of the microcave cavity has the potential to expose your eye to the full brunt of the standing wave peak without much other body mass in the way to absorb the energy, creating the potential for that intense localized heating.