If you're hiking in the Sierra, there are non-DEET repellents that are quite effective (rate as highly as lower concentrations of DEET, and less toxic). I can't speak to elsewhere (except I did use Bite Blocker near Juneau in August successfully years ago). I've used two very successfully in the Sierra over the years: Repel with oil of lemon eucalyptus, and Bite Blocker. There's another, which I haven't tried yet, that's supposed to be even longer-lasting than DEET, called Bio-UD. click here for study Don't even try Citronella or any of the other "natural" repellents, they don't work much at all.