Common hazardous ingredients
Amitraz, fenoxycarb, pennyroyal, permethrin, propoxur and tetrachlorvinphos.
Do not use "pool grade" diatomaceous earth for flea control.
Potential hazards
Products applied externally should be used carefully because they can harm other insects and marine life.
Use
Use according to label instructions.
Avoid foggers and any broadcast treatments. Avoid over-the-counter flea and tick collars. Pesticide levels from some flea collars can be many times higher than the U.S. Environmental Protection Agency's acceptable levels for adult safety.
Alternatives
Herbal products containing essential oils of cedarwood, lemongrass, peppermint, rosemary and thyme are nontoxic and safer than chemical treatments. (While limited testing has been done to measure effectiveness of herbal products, they may be worth trying before resorting to more toxic methods.)
Ask your vet about an Insect Growth Regulator that contains s-methoprene, lufenuron, or pyriproxyfen or a product containing nitenpyram or spinosad. Some of these are taken orally as tablets or injected and are believed to have few or no health affects on humans and be generally safe for pets.
As a last resort, talk with your vet about a product that contains fipronil, imidacloprid, meta-flumizone, pyrethrins or selamectin. These chemicals are safer than some products, but should be used with caution and should not be used if you have children or if you are pregnant. Never use permethrin and pyrethrine on cats.
Learn about nontoxic flea control