Pregnancy Nose

"There doesn't seem to be any sort of adaptive mechanism to blame for a pregnant woman's sensitivity to certain smells." Brenda Stokes (Baby Center). Michael's theory has something to do with cavewomen using the hormone related sensitivity to smell to stay safe while the men were away and stay clean while pregnant. However, whatever it may have been useful in doing historically it is certainly a deterrent to functioning in modern society.
Maybe it's our body's way of slowing us down or keeping us away from potential hazards. "According to a 2004 study published in Chemical Senses, over 40 percent of pregnant women tested in the first trimester reported increased sensitivity to the smell of cooking odors, cigarette smoke, spoiled food, and perfume." In the first weeks of my pregnancy a sink full of dirty dishes made me sick and kept me out of the kitchen (off my feet a lot more because I wasn’t doing any dishes) for about a month. The litter box or a full garbage can were equally dangerous smells. Obviously, things like that are full of germs and the pregnancy antibodies take a little while to build. There's also chemicals like cleaning products or the worst of all cigarette smoke are certainly potential hazards.
There also the food smells. I remember my cousin telling me she realized she was pregnant when she walked into her parent’s house and the smell of popcorn made her sick. My earliest memory of a food smell that made me sick was greasy breakfast meats. Certainly not the healthiest choice for a pregnant woman. But there's also things like the smell of peanut butter which still bothers me and there's certainly nothing particularly hazardous or unhealthy about that. Maybe there are exceptions to the rule. The other possibility is none of the rational theories apply to hormone induced symptoms, who knows?