Cats, Fleas and Pennyroyal Oil

In the past I have used a drop of pennyroyal oil on the top of my cat's head to repel fleas. I have heard that this oil should not be used due to the possibility of ingestion (hence, on the top of the head...) but I know they could still be licking it off. Would diluting the oil and possibly adding a little pyrethrum oil make it safer? I'm also trying nutritional yeast in the diet and have resorted to diatomaceous earth rubbed into the fur (though this seems to dry their skin out, too). I've never had a flea problem when I used the pennyroyal, but I don't want to endanger my pets. I know the discussion on fleas on cats is long, but I wonder about diluting the oil to make it safer.

I have never been a fan of employing essential oils on animals. Although there are some references that cite their use, I believe that the indications given are derived from the perspective of humans. For instance, it is believed that animals rely on smell rather than their sense of taste in order to survive in the wild. Moreover, it has been recorded that dogs are able to detect smells at 1:1000 that of humans. This statistic means that dogs' and cats' ability to sense odours is vastly superior to ours. Therefore, we have no idea what effect the smell of an essential oil will have on an animal nor what that animal experiences when that essential oil is absorbed through the skin. Pennyroyal oil in particular can be toxic, especialy in or on cats. Therefore, please do not use this oil or any essential oil on your cat if at all possible.
If fleas are a problem, the most common reason is that the cat's health is not at its optimum. Fleas, being parasites with short life cycles, only attack a host whose body is not functioning as well as it might. Therefore, I would suggest that you strengthen your cat's vital force by feeding it a good, homemade diet (See this website (www.richters.com) for the posting, "Aging Dog with Arthritis" for sources that list recipes). In order to deal with the fleas that presently exist, you might want to look at the formula for "Lemon Lotion" in Juliette de Bairacli Levy's book, "The Complete Herbal Handbook for the Dog and Cat" or try doing a herbal rinse with the herbs Feverfew herb (Tanacetum parthenium), Calendula flowers (Calendula officinalis), Celery seeds (Apium graveolens), Yarrow herb/flowers (Achillea millefolium) and Mullein flowers (Verbascum thapsus). Fleas will still need to removed with a flea comb and drowned in a jar of soapy water and you will also still need to clean the house thoroughly to remove any fleas or lavae that may be waiting to start their next life cycle.