That is one of those subjects people feel strongly about. Our cat just lost her fairly new flea collar, but we need to get another open on her, as she is nursing kittens, and when we put the flea drops on her and them, she washed it all off and got herself sick. She does not normally wear a collar, but didn;t seem bothered by it overmuch. She is a farm cat and great mouser, p[probably where the fleas came from.