Just to let you all know, did half listerine and half water, sprayed the dogs, rubbed it in well. This am, only a flea or two, and they were loaded! Also sprayed bedding and anywhere they sleep, rugs, etc., and the firewood I've brought in so far (figure that's where they came from). It's a little sticky, but a quick brushing got rid of it. They smell pretty good too, used the mint flavor LOL. So, apparently, it works! A lot cheaper than the spot junk too. And they tolerated it quite well, no problem...
I'd just be careful if the skin is really not intact (like from rash or scratching). Listerine usually has a lot of alcohol which on its own can be pretty irritating, but if it gets absorbed (due to non intact skin) could potentially cause problems (like seizures).
Just my $0.02.