About 50% of adults in the U.S. have chronic plant and dust allergies, a lot which which can be attributed to 1) the overuse of household cleaners, and 2) sitting indoors and never going outside. NY is particularly bad, there's even an unofficial condition "New York Nose" that both my parents claim to have.
The MCS disease in Safe (haven't seen it) sounds a lot like psychogenic parasitosis, which also afflicts predominantly white, predominantly middle class women (a lot like mild-moderate depression). These women are convinced they have bugs living under their skin, so they spend hours and hours cleaning themselves and their homes trying to get rid of them. Some doctors think it's a real parasite that mostly affects women who've had children, since it's seen sometimes even in African mothers. Some think it's completely in their heads. (The "parasite" metaphor's pretty obvious from that perspective- unwanted kids/family.)
I go with: study it to make sure it's not psychogenic, but make sure they get psychiatric help, too.