The best way to control fleas on cats is a topical medication applied to the back of the neck such as Advantage or Revolution. Flea collars offer slight protection, but they can be more harmful to the cat than to the fleas.
Flea collars can cause irritation where they rub against the cat's neck. Long-term use can cause a permanent loss of hair where the collar sits.
Do not use collars containing permethrin unless they are specifically labeled for cats. Permethrin in high concentrations can lead to seizures and death in cats.
Cats have a high sensitivity to products containing organophosphates. Exposure can lead to drooling, difficult breathing, weakness and seizures.
Chewing and Choking
Make sure your cat cannot chew on any part of a flea collar and ingest the ingredients. Another danger of any cat collar is the possibility of it catching on something and choking the cat.
Do not use flea collars on kittens, chronically ill cats or elderly cats. They might be extra-sensitive to insecticides.
Read the Label
Always read the label of any flea control product for your cat and never use a product that is intended for a dog. That mistake could be fatal to your pet.