Permethrin Info

Mods - please remove if not allowed.

In a recent post- u/tetrasomnia raised an important question asking if dried permethrin was safe for cats. To prevent any misinformation: The answer to this question is no. And here's why:

Dry permethrin is less deadly - but if ingested can still cause your cat problems. So basically- if your cat licks your permethrin treated dog/stuff your cat can have major problems due to permethrin toxicity.

If you're curious- here's a bit of the chemistry. Permethrin is a ~~hydrophilic~~ hydrophobic crystalline compound that will not dissolve in water but will dissolve on oils and other chemicals (organic solvents like methanol, chloroform, acetone, etc.).

Commercial permethrin is a generally an emulsion- so the chemical is made into a liquid by dissolving it in an solvent like mineral oil and then suspending droplets of it in water. While permethrin will not solubilize in water based saliva- saliva contains all kinds of fun things from the environment. For cats- that groom themselves by licking- they can pick up skin oils in their saliva. Permethrin can solubilize in oil.

Think of it like spilling pasta water and letting it dry. Starch from pasta is suspended in the water- so if you spill your pasta water on your countertop you will see the starch from your pasta after the spill dries. You can scrub it off (with an abrasive kitty tongue) or use a solvent based cleaner (acts like kitty skin oils) to remove the starch (permethrin).

So while dried permethrin is less immediately harmful- it wouldn't take much to get into kitty saliva.

Source: I've got a PhD in Molecular Biology w/extensive experience in applied biochemistry.