I know I saw this episode. I have checked every episode of The Twilight Zone and Outer Limits. Can't find it. The episode is black and white. The astronaut returns to his home and there is a lot of interaction with his wife. He slowly realizes that there are changes occurring in his body as he is beginning to develop a crust or hard shell until eventually he morphs into a creature more like a large insect than anything human. Presumably he has contacted something in space which is triggering this metamorphosis into perhaps an alien species. There are scenes with NASA or space administration doctors who of course don’t know what’s happening to him either.