One type of flea collar works by emitting a substance that is toxic to fleas. Another type works by causing a substance toxic to fleas to be absorbed into the host animal's subcutaneous fat layer.
Flea collars that simply emit a toxic substance mainly kill fleas close to the collar area. These types of flea collars are not as effective at killing fleas as collars that allow flea toxin to be absorbed.
There are many types of effective flea control products including oral medication, spot-on treatments, flea sprays, dips and powders. It is essential to disrupt the fleas' life cycle to control an infestation.