
Originally Posted by
icmmendoza
Veterinarians have had some concerns that the chemicals in flea and tick collars could be dangerous for pets and children (see "Chemical Flea Collars Threaten Pets and Kids, as Well as Pests" and "Poisons on Pets" under "References" below). Studies have shown the chemicals in collars made by major pet products companies can damage nerves and possibly cause cancer if used over a long period of time. The study also cites potential risk to kids, who pet the animal, get the chemicals on their hands and then place their hands in their mouths.
Source: eHow.com