The Comfortis chewables have one great advantage over conventional spot on flea treatments – it acts faster, a lot faster. Where conventional flea control programmes take 24-48 hours to work, Comfortis starts acting within 30 minutes. Fleas literally don’t have a chance to lay an egg. All fleas in your dog’s coat will be killed within four hours after he’s taken the tablet. The secret ingredient is Spinosad. It works for up to one month and as it’s not an external treatment, your dog can swim as often as he likes.