I may be wrong, but I feel like I read the Sentry ingredients and was kind of leary about it. I feed raw and like to be as natural as possible, but IMO the natural stuff doesn't work in high risk areas. Last year I applied Frontline Plus once in the summer, when I saw a flea on Cabo. This year I applied it three times, ticks are so bad this year and we like to hike in the woods. After pulling more off the dogs than I can count, finding them in my bed and crawling on my walls, I put Frontline on them and kept up with it over the summer. It is the topical I feel safest using, and it works for us. They got it applied three times the year, I am going to try not to use it anymore the rest of the year and see how it goes.