So, our hike in the Harrison Hills region was a real wakeup as to the effectiveness (or lack thereof) of DEET, the most common active ingredient in bugspray. I sprayed myself up good, but it wasn't effective in the least. Not even with periodic reapplication from the travel-size 100% DEET sprayer I had in my bag. I don't know if it was NEVER effective, or if it's possible for insect populations to build a resistance to it, but whatever the reason, whatever it's history, it was clear to me that those familiar green cans weren't going to cut it.
See, I intend to go back into those hills, and I believe in preparedness. So I did my homework afterwards, and I tested a combination of two different sprays. Permethrin, which is used to treat clothing and equipment and Picaridin, which you can use on skin like DEET. Permethrin is safe to get on your skin, it's just ineffective on it. It only works if you get it on your clothes and boots and pack and tent. The upshot is, Permethrin doesn't just repel insects, it kills them. It's a chemical they derive from chrysanthemum flowers. But, a word of caution, it isn't safe for cats. So if you've got cats, make sure to throw your hiking clothes right in the wash.
Picaridin I know relatively little about. It might be made out of space captains. Nah, I did look into it and it's derived from a plant related to where we get black pepper. It was developed by Bayer in the 80s, but only approved for use about a decade ago.
Permethrin can be effective for up to two weeks. Picaridin's effective time is around 8 hours.
They can be used together, and they're what I used for the rest of the summer. They're relatively low odor, and not nearly as unpleasant as putting on DEET can be. Presumably you could all three, I haven't seen anything warning you not to. But just the combination of Picaridin and Permethrin was enough to prevent me from seeing another tick all summer long.
If you'd like to pick some up, this handy, portable pump of 20% Picaridin from Sawyer is as high a concentration as you'll find, the stuff I got from Fleet Farm in a red can was only 5%. And this spray can of Permethrin is what I've been using through out the summer. Fortunately, with that, you don't need to carry it on the trail. You can leave it in your car, or back at home.