snopes.com: Wasp Spray
However, some have advised against adopting wasp spray as an alternative to pepper spray, primarily for two reasons:
The active ingredients in most wasp sprays are pyrethrins, compounds derived from a species of the chrysanthemum plant which penetrate the nervous systems of insects and kill them. Since wasp sprays are not formulated to be used directly on human beings, some critics maintain, they should not be relied upon as a form of non-lethal self-defense, as their safety and effectiveness for this purpose has not been sufficiently tested, and the toxic effects of pyrethrins could potentially be much more harmful or less effective than expected.
Many jurisdictions specifically prohibit the use of any self-defense sprays other than pepper spray. (Additionally, most spray insecticide containers include warnings stating that "It is a violation of federal law to use this product in a manner inconsistent with its labeling.")
The primary benefit claimed in advocating the use of wasp spray over pepper spray is that the former can be effectively deployed from a greater distance ("wasp spray can shoot up to twenty feet away and is a lot more accurate"). However, canisters of pepper spray with an equivalent (or greater) range are commonly available: Some of our pepper spray will produce a concentrated stream of about 8 feet up to 25 feet in distance. Other sprayers produce a cone spray pattern and others models produce a fog that covers a larger area.