The two literal senses of nauseous, “causing nausea” ( a nauseous smell ) and “affected with nausea” ( to feel nauseous ), appear in English at almost the same time in the early 17th century, and both senses are in standard use at the present time. Nauseous is more common than nauseated in the sense “affected with nausea,” despite recent objections by those who imagine the sense to be new. In the sense “causing nausea,” either literally or figuratively, nauseating has become more common than nauseous : a nauseating smell.
c.1600, "inclined to nausea, easily made queasy" (obsolete), from nausea + -ous. Sense of "causing nausea or squeamishness" is attested from 1610s. For distinction from nauseated see nauseate. Related: Nauseously; nauseousness.