A year−long study of anti−flea products conducted by the EPA concludes that these products can be harmful to pets, especially to smaller breeds of dogs. New instructions and warnings will be appearing on these products within the next several months.

The products in question are small vials of liquid pesticide that owners apply to the back of their cat or dog, usually monthly, to kill fleas and ticks. Unfortunately, they can also kill your pet. There were about 600 deaths of dogs and cats reported in incidents involving the products in 2008.

These products are poisons, not medicines. Because fleas are so tiny, it's theoretically possible to poison them without harming the pet. But in smaller pets, this margin of safety may disappear.

There has always been some controversy about applying pesticide containing preparations to pets. This escalated dramatically in 2008. That year, reports of adverse reactions on pets rose from 28,895 to 44,263, an increase of 53% over the previous year.

Many of the incidents were minor, such as skin rashes, but others were not. Vomiting, diarrhea and seizures occurred. And there were those 600 deaths.

The increase in incidents seems to be due to the potency of two pesticides, permethrin and cyphenothrin, now used in anti−flea products. Permethrin is especially dangerous for cats and is not supposed to be in any anti−flea product made for them. But sometimes owners apply preparations meant for dogs on their cat, often with disastrous results.

Small breeds of dogs, those weighing between 10 and 20 pounds, are most likely to be harmed. Chihuahuas, Shi−Tzus, miniature poodles, Pomeranians and dachshunds had the most reported incidents. Together, they made up 33% of all cases for cyphenothrin−containing products.

Shi−Tzus, Bichon Frises, Chihuahuas, Yorkshire terriers and Maltese were involved in over 25% of the reported incidents in permethrin−containing products.

The problem may be in the dose. These products are poisons, not medicines. Because fleas are so tiny, it's theoretically possible to poison them without harming the pet. But in smaller pets, this margin of safety may disappear. The new regulations are expected to make clear that these products must not be used on smaller pets.

With over 40,000 adverse reactions reported in a single year, it probably makes sense to talk to a veterinarian before using any anti−flea or tick product on your pet. And even then, to consider whether using them is really necessary, depending on where you live.

An article on the dangers to pets from commercial anti−flea products was published online by Scientific American on March 18, 2010. The article is freely available. Customer comments that appear after the article suggest that these products can cause big problems for big dogs, too.