Tragically, all-too-many people have learned the hard way that not all flea products are safe, and it astounds me that some of the store-bought flea products weren’t taken off the shelves years ago when they began causing deaths and serious complications.  Some common mishaps include products intended for dogs being used on cats, and improper administration such as putting a topical product in the animal’s food.  Cats are much more sensitive than dogs to these products, essential oils, and other remedies like garlic, so it’s best to check with your vet before using anything on your cat.  It is not safe to use any spot-on product containing permethrin in cats (like Advantix).  If an animal starts acting unusual after applying topical flea treatment, they should be bathed right away to remove as much residual product as possible, and should be seen by a vet immediately.  Cats can be bathed with dishwashing liquid (not dishwasher detergent). 

An informative report can be found here:  Journal of Pesticide Reform from the Northwest Coalition For Alternatives To Pesticides/NCAP.

Here are some safer alternatives to pesticides:

• My personal favorite is adding Brewer’s Nutritional Yeast (not the baking kind) to my animals’ food. The rule is 1 tsp/30 lbs, though I use less, usually just sprinkling it all over the food (there is also a pill form). This provides them with lots of B vitamins that help the immune system, which is key for keeping fleas away, and some theorize the fleas don't like the taste. It is true that a healthy animal won’t attract fleas as much as an unhealthy animal, so things like diet are a big part of preventing fleas. Garlic is also recommended (there are formulations made with both Brewer’s Yeast and garlic), but giving cats garlic is not recommended. Raw, unaged garlic should never be given to cats or dogs. Like onions, garlic can cause Heinz body anemia.
• Neem oil is a favorite remedy and is incorporated into many different natural products that are readily available.
• Fleas can be deterred by having a bed stuffed with cedar shavings mixed with crushed neem leaves, and dried rosemary and lavender.
• Green Hope Essences makes a product called “Flee Free” that combines many different flower essences that help keep fleas away. Again, essential oils should NOT be used with cats.
• For dogs only: A few drops of oil of lemon and eucalyptus, neem and karanja, or cedar and peppermint in warm water, shaken well in a spray bottle, and spritzed on the fur, especially on the ear tips, and at base of the tail can repel fleas, ticks, and mosquitos. There are herbal preparations and shampoos available, often containing d-limonene, from citrus, or herbs and essential oils such as citronella, eucalyptus and cedar.
• Slice a lemon and put it in a cup of boiling water and allow it to stand for some time (even overnight) to have a potion that can be applied to a dog’s fur (not for cats).
• If there is not a cat living in your house, Citrus Peel Extract can be effective for the environment, but should also be used with caution and ventilation. Two teaspoons per two cups of water can be sprayed on the dog’s bed. Citrus shouldn’t be used around cats.
• Flea Control Nematodes from Gardens Alive! help control fleas in outdoor areas, making it less likely that fleas will be brought inside on your animals. These beneficial nematodes control fleas by killing them in the larval and pupal stages in the soil where they live, breaking the lifecycle.
• Boric acid and borax are also widely used against fleas in the environment. Sprinkle a thin layer of boric acid or borax on carpets, leave on for a few days, and then vacuum up.
• There are commercially-made flea traps, or you can make your own by positioning a small lamp with a 20 watt or lower bulb over a shallow dish of soapy water or vegetable oil (especially helpful if there aren’t any warm-blooded bodies around).

This list is by no means complete.  Other important factors include frequent combing with a flea comb, disposing of any fleas in soapy water, frequent vacuuming, and frequent bathing.  There are many products out there that might be helpful like Herbal Flea Pet Powder by NaturVet for dogs and cats, and FleaDerm Cream by Pet Alive for the dreaded Flea Bite Dermatitis.