Why do I feel nauseated by smells that never made me feel sick before?

Oversensitive senses. The reasons for increased sensitivity to smells, and the cravings for and aversions to foods in early pregnancy are not clear. These probably had some survival benefit long ago, helping pregnant women to avoid foods that could harm a developing fetus. The biological reason is felt to be the elevated hormone levels of pregnancy but no one knows why some women are more severely affected than others.