If you really want to be correct, you will use nauseated, not nauseous, when describing the state of being afflicted with nausea. Nauseous, on the other hand, is really supposed to be used to describe something or someone that causes nausea.
We nurses can do a lot to turn around the deplorable trend amongst the common populace to use these words incorrectly. We deal with nauseated people on a daily basis. We can gently educate the public by being role models for proper usage!
(nauseous-correct usage): The smell of rotten eggs is nauseous.
(nauseated-correct usage): The smell of rotten eggs makes me nauseated.
