As most people know, there are hundreds of different medications for fleas (i.e. sprays, collars, powders, washes, tablets, bombs, herbal remedies, shampoos etc.) All of these things do kill fleas, but there is a very good reason why most will not solve your flea problem.
For every flea on your pet, there are literally hundreds of eggs, larvae and pupae in the environment, whether that is in the house, in the yard, under the house, etc. What that means is, when we wash our pets for fleas, it does kill those fleas on the pet but does not stop other fleas jumping on. So what you find is the next day your pet has just as many fleas again.