Why all the safety concerns regarding topical flea products?

Question

I don't use topical flea products on my cats or dogs. I worry about using a pesticide that is absorbed systemically. This is just my own personal concerns and not intended to alarm people.

I was looking for a reference to answer "How should I schedule application of flea preventative against bathing?" and got sidetracked after discovering negative search results warning about topical applications. The results just reinforced my concerns, but maybe I'm just a bit too worried. It is also difficult to know if I can trust everything I read, as I am not sure the search results will be reputable.

Are topical flea products safe for dogs and cats?

Answer 1

Pretty much all flea treatments marketed for pets are toxic in the same way that coffee and chocolate are to people: a high enough quantity will cause problems.

If health concerns are genuinely a problem, you may want to look at Diatomaceous Earth for flea control purposes.

What is Diatomaceous Earth?

Diatomaceous earth consists of fossilized remains of diatoms, a type of hard-shelled algae. It is used as a filtration aid, mild abrasive in products including toothpaste, mechanical insecticide, absorbent for liquids, matting agent for coatings, reinforcing filler in plastics and rubber, anti-block in plastic films, porous support for chemical catalysts, cat litter, activator in blood clotting studies, a stabilizing component of dynamite, and a thermal insulator.

How it works

Fleas and other insects with an exoskeleton (hard shell) are susceptible to the glass-sharp edges of the microscopic diatoms. The silica shards cut through the waxy exoskeleton surface, effectively drying out the flea, resulting in death to these types of insects and their larvae.

Source

Because DE is not a poison or toxin, insects cannot build up immunity to it. Also, it does not reduce in potency: as long as DE is still present, it is just as effective as when you first applied it.

Safety concerns

Provided you get food grade DE, it is completely safe to touch and eat (in fact, it is commonly used for pest control on food crops intended for people, so there is a chance that you ate some recently). However, it is not good to inhale.

Unless it is labeled 100% DE, it likely contains poisonous additives that your pet should not have. If the label says "do not use on food", then don't use it on your pet. You will likely need to seek out a natural food store or special order it online.

More information: http://www.fleacontrolbook.com/naturalfleacontrol/diatomaceous-earth-the-a-miracle-cure-for-flea-control/

Answer 2

"Safe" really depends on your tolerance for risk. For example, I don't give my cats a topical pesticide even though mosquitoes can come into the house (open doors when we go in/out) and they can bite my cats and give them heartworm. I've judged that the risk of them getting heartworm is less than the risk of problems from putting the products on their skin.

A good resource for investigating the risks involved in various flea treatments is this pdf from Greenpaws. It lists what is known about each flea preventative/treatment. As an example, this is the info given for Selamectin (the active ingredient in Revolution, which is a popular vet recommended treatment).

Selamectin is a relatively new insecticide and little information exists on its toxicity. However, early evidence suggests that Selamectin has very low toxicity in mammals and chemically similar compounds have not been found to be carcinogenic. Measurable transfer of residues from fur has been detected and further safety evaluations are needed.

Each statement has several references so you can look further if you're interested.