As we all know the main ingredients of flea medications are pesticides. I am aware of that so I try to use it as carefully as possible. According to some web sources (including NCAMP Factsheet), sunlight degrades Fipronil to Fipronil-desulfinyl which is 10 times more toxic than Fipronil. Since Frontline makers recommend keeping my dogs from contacting water for 48 hours after Frontline application, I figure that is how long it takes for Fipronil to be absorbed into the dog's system. I don't know exactly how this topical medications work (do they spread through blood circulation, or do they spread through the skin?) But in order to minimize Fipronil-desulfinyl, should I apply Frontline and keep the dogs inside and go for walks only at night, for the 2 days after the application? Is this a logical approach? Just FYI, it's not just UV ray, but the sunlight causes it.