Tetrachlorvinphos: According to the EPA and the Humane Society, side effects of overexposure can include nausea, dizziness, confusion, and even paralysis and death in humans, especially children. This ingredient is use in Adams, Hertz, and Zodiac flea collars.
Pyrethroids: The Agency for Toxic Substances & Disease Registration, a subsection of the CDC, says that humans exposed to pyrethroids can experience numbness, itching, burning, stinging, or tingling. On the label, pyrethroids are any ingredient that ends in “-thin” (permethrin, deltamethrin, flumethrin, etc,) and etofenprox. These ingredients are found in several types of medication from K9 Advantix, Frontline, Hartz, Sentry, and Zodiac.
If you have a cat, avoid medication with pyrethrin, a natural insecticide derived from chrysanthemum flowers. It’s safe for dogs and humans, but it can trigger seizures in cats. Our top picks happen to be pyrethrin-free, though many shampoos, sprays, and powders are not. If you have a cat that cuddles or grooms your dog, double check your ingredient labels.