This 7 Dust discussion - demonstrating the 'what we know now' vs. 'what we knew then' - is part of why I suggested diatomaceous earth [in this interaction with Wurwulf:
http://forum.rifftrax.com/index.php?topic=3699.msg726251#msg726251http://forum.rifftrax.com/index.php?topic=3699.msg726258#msg726258http://forum.rifftrax.com/index.php?topic=3699.msg726337#msg726337]
Diatomaceous earth is not a chemical. It is stone powder. So as long as one doesn't inhale it directly, it is basically inert. That cannot be said for the multitude of neurotoxic chemicals that are sold for flea treatments, all of which are damaging to living tissues. If they weren't damaging to living tissues, they wouldn't kill the fleas.
Look up online all the ingredients listed on any flea treatment you plan to use. See if you want that applied to a critter you love, or when you pet it, have rub off their backs, necks, heads, bellies onto your skin where you can ingest it [as the animal cleans itself, it spreads the oil suspension around so that it is all over]. Plus, your pet will lie down on a large number of pieces of furniture that your family will then sit or lie on. They may lie on the floor where children might play, do you want those chemicals being ingested by a child [presuming you have one or more]?
Those chemicals don't 'evaporate' and become inert after a couple days. Only the most reactive of chemicals break down in a short period of time. [Last I read (about a decade or so ago) there was still measurable DDT in the dirt and food chain in this country. It's use was discontinued in the early 70s.] The couple day waiting period after using a flea treatment is just when they are intensely concentrated on the pet. After that, they are inside your pet, and on your skin (in your body, if you ate food by hand after petting your pet without washing your hands first), and on your furniture.
The Environmental Working Group [name is link] is a good place to find out about the toxins that are in items you use around the house all the time (e.g. cleaning products contain a multitude of chemicals that are toxic to humans and animals, including, for instance, chemicals known to cause severe respiratory problems in products in spray containers, so they are inhaled any time they are used).