The chemicals that were used to control pests are generally insecticides. Consumers use this to kill fleas and other parasitic insects or acaricides to kill ticks and mites, which are arachnids. In the correct dose, most are very effective on fleas and ticks and safe for both you and your pets. However, not all of these are equal. So before selecting a product, always check the active ingredients as some are not particularly good or safe.
Deltamethrin is a synthetic pyrethroid and one of the most effective and safest insecticides out there. It works by disrupting the normal nervous system function of the pests. This happens by interfering with the sodium channel of nerve cell membranes. And then results in a delay in repolarization of the nerve and finally killing of the parasite. These insecticides will kill parasites either through contact or ingestion. It first came to market in 1978. It was then shown to be very effective at killing fleas with minimal adverse effects on either humans or dogs.
Flumethrin is also an ectoparasiticide of the synthetic pyrethroid group and provides acaricidal capability and kills several variety of ticks and also repels them. It reduces the risk of them biting and reduces the risk of Vector-Bourne Disease transmission e.g. Lyme's Disease.
Imidacloprid works on flea larva, adult fleas and lice. It becomes effective against the most common fleas as soon as the collar is on your dog. It works by attacking the central nervous system (CNS) of the flea leading to paralysis and death. Imidacloprid barely reacts with the nicotinergic receptors in mammals and has trouble crossing the blood-brain barrier so it has virtually no effect on the CNS of mammals like us or our dogs and so is safe in the right doses.
Pyriproxifen is another safe insecticide that works by targeting the flea eggs and larvae instead of adult fleas. It makes them unable to reproduce, so they die within a generation. It is often used in conjunction with Deltamethrin to effectively control fleas at all stages.
Propoxur also attacks the nervous system of fleas. But unlike Deltamethrin it can be harmful to humans.
Tetrachlorvinphos (TCVP) does kill fleas but it has some very nasty side effects to both humans and pets and consumer must avoid it whenever possible. TCVP is a human carcinogen and children are particularly vulnerable. So if you see this listed as an ingredient on the flea collar you are looking at, look for something else.