Believe it or not, I had good luck with Avon's Skin So Soft diluted with Water and sprayed on. Gnats were a big problem for me when I used to work in the yard in MN, and that was what was recommended and it seemed to work pretty well. I took a bottle with me to GG last week, but it wasn't needed...
Not sure why it works, maybe you just smell too pretty or your nice soft skin just isn't attractive to them anymore???
