This is something I found a few years ago which I remember when I was typing the soap comment:

"The word permethrin is a generic name of a group of pyrethroid chemical isomers. This is like saying everything with the word soap is the same thing. Put your wet hand into a box of powdered laundry detergent and see if it is the same as a bar of ivory, but they are both "soap".

Without exception, these other products use a much more toxic isomer as they are all designed to be applied to material that maybe will have the potential for contact with mammals, which have a completely different physiology than reptiles do. These products are designed to be as toxic as possible to get a quick "knock down". These higher toxicities will not harm mammals, but are documented to harm lower vertebrates, including reptiles, fish, amphibians, mollusks and so forth and therefore can be used for these other uses. Also, only a very small percentage of what is in the can is the "active" ingredient, the rest is always a trade secret of the company, so will never be disclosed (only the generic active name has to be disclosed under EPA regulations). Different isomers have differing toxicities and again, only a range of the cis-trans ratio is given on a label, so one can never find out what is really in the can (again trade secret).

Since a product is only approved by the EPA for the uses listed on the label, chemicals in the formula that are not toxic to the host for the testing submitted, doesn't mean they would not be toxic to a host not listed. In fact many of the "inerts" used in these permethrin formulas are toxic to reptiles. If the company tried to receive EPA approval with these formulas for use on reptiles, they would not, as the EPA would not allow a product to be sold that would harm the host listed on the label. This is why the EPA regulations state that it is a federal offense to sell or use a product inconsistent with the label, not only because of the risk to the host, but also because such usage can create resistance.