The unique new ingredient Spinosad is the active flea-killer in a tasty beef flavoured Comfortis chew. Within 30 minutes it will start knocking down fleas and 4 hours later all fleas are dead. It works so fast, fleas literally don’t get a chance to lay any eggs. It should be chewed monthly for long-lasting protection. Lilac is free to swim or bath as much as she likes, as Comfortis works internally and cannot be washed off the skin like other flea control products.