I have not tried this but I read on the internet somewhere that a capful of cider vinegar in the dogs water is a natural flea deterent. I do not have problems with my dog being allergic so I use Frontline. This is a once a month product that also kills Ticks which are prevelent in our area.

If you have any questions the best place to start is with you vet. They can recommend products that should be hypoallergenic. If you don't get answers from them there is a ton of info on the net. Do a search on flea control. Good Luck.