The egg and pupa are virtually impossible to kill. The vulnerable stage is the larvae. Prior to the advent of of Program, veterinarians advocated putting borax powder in people's carpets. This killed the larvae and eventually stopped flea reproduction in the home. Now by giving oral Program once a month, the flea eggs that are laid and deposited in the home cannot hatch to larvae.
Program is a safe and non-toxic method to control infestations indoors.
The problem came because many dogs and cats go outside and thereby pick up fleas that have not been exposed to Program. These fleas can therefore lay eggs that can hatch and in turn set the four fleas stages in motion. The other problem was that Program did not stop fleas from biting dogs and cats. Many dogs and cats are allergic to flea bites. This means one flea bite can make the pet itch and scratch uncontrollably.