Fleas can be an on-going battle. One doesn't want to be so heavyhanded with chemicals that the immune system is impaired, but at the same time one does not want the flea to take over and create an infestation that will also cause disease. Brewers yeast and garlic can be effective flea deterrents. The sugars in some commercial cat foods may also make an animal more attractive to fleas and they are particularly vulnerable if they have a weak immune system. It is therefore very important to feed pure foods - whether cooked or commercial - and to supplement with a good feline multi vitamin and mineral formula.
The main anti-flea herbs are eucalyptus citronella, cedar, rosemary and fennel which can be pulverised and made into a flea powder. you can also make good herbal collars from herbal oils.
Corpore Sano is a good anti-parasite shampoo. Juliette de Bairacli Levy also recommends her Lemon Skin Tonic, whiich is made by putting a sliced lemon into almost boiling water. It should be left to cool overnight and then put on the coat of the cat in question and can be used on a daily basis as it is harmless.
A flea comb is the other important piece of equipment as it picks up fleas as it moves through the fur, the fleas can be drowned in hot soapy water or popped between two thumb nails and squashed.
If things cannot be controlled herbally then use a chemical spray and do NOT overdose on any account.
Just as important as the products are regular vacuuming and washing of bedding - which should be picked up carefully so nothing falls out - to get rid of flea dirt and eggs. The bedding should be washed in hot water. Lavender can be left near the bedding as fleas dislike it. I use the Lemon trick on my own cat Beauty and in seven years not one flea!