Quick answer
Traditionally, nauseated means feeling sick and nauseous means causing sickness — so a nauseous smell makes you nauseated. In current usage nauseous overwhelmingly means "feeling sick", and dictionaries record it. The traditional distinction survives mainly in careful writing.
The core difference
A traditional split that everyday usage has largely collapsed.
- nauseated (traditional) — feeling sick: I felt nauseated.
- nauseous (traditional) — causing sickness: a nauseous stench.
- nauseous (current) — feeling sick, in the great majority of use.
The parallel that explains the objection
Compare poisonous: a poisonous plant causes poisoning, it is not itself poisoned. By that logic a nauseous thing should cause nausea. That is the argument, and it is a coherent one — but usage has moved, and "I feel nauseous" is now standard.
The unambiguous option
Nauseating means causing nausea and is not contested by anyone. If you want the causing sense with no risk of being misread, that is the word.
Frequently asked questions
Is "I feel nauseous" wrong?
It is now standard and recorded in dictionaries, though traditionalists prefer nauseated for feeling sick.
What word means causing nausea?
Nauseating is unambiguous. Nauseous traditionally meant this but is now mostly used for the feeling.
What is the argument for the traditional split?
By analogy with poisonous — a poisonous plant causes poisoning rather than being poisoned.
