As a kid (late 70s, I think maybe early 80s,) there was a Saturday cartoon filler where there were two men running around a crashed spaceship. One would sneeze and turn into a monster. The other would stick his finger under his nose to prevent the sneeze. I don't know why, but not knowing what this is has been bothering me for years.
This would have been in Wisconsin, if it was a regional only show.
I want to say that you saw an episode of the Sid and Marty Krofft children's television series Far Out Space Nuts (with Bob Denver from Gilligan's Island,) but I can't find a preview of an episode that matches.
The episode that comes to mind is titled "The Crystallites."
From Wikipedia:
The Crystallites hand pick Junior for a very short reign as their king. Meanwhile, both Junior and Honk turn into green-furred monsters after ingesting a mysterious "coconut milk".
My memory says that the two guys ended up running around the space ship, sneezing and turning to the monster and back.
After some more searching, I found the Far Out Space Nuts episode "Crystallites" on the Internet Archive.
It does indeed have Junior (Bob Denver) switching between human and monster every time he sneezes after drinking some milk from a "coconut" found on a strange planet.
Here's Bob Denver as the monster:
Only Junior and the fuzzy critter "Honk" did the monster thing. Barney stayed human the whole time.
