It depends on what you are applying it to. Permethrin is meant to be applied to clothing or gear, not to your skin. DEET is meant to be applied to your skin, and can eat holes in your clothing or gear depending on the material.

So the correct answer is DEET and permethrin. Kill ’em all.
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“Hiking is just walking where it’s okay to pee. Sometimes old people hike by mistake.” — Demitri Martin