You are nauseated when you are grossed out by something. "Nauseous" is used to describe something that makes you nauseated. You can however, be "nauseous" if you don't bathe and brush your teeth for a few days.<quoted text>
When I was a kid both of my parents smoked. Back then it wasn't unusual for people to smoke in their houses and cars, and my parents did both.
I remember how sick I would feel in the car with them. Nauseated. Headache. it was so miserable. I am so glad I never smoked.