Cats and Essential Oils
Cats are obligate carnivores. That means they eat meat, and pretty much only meat. Their bodies lack the enzymes to process a lot of plants and that is why so many are toxic to them. Essential oils are distilled plants and therefore many essential oils are toxic to cats. The best way to figure out which ones you can diffuse around your cat is to look up and see if that plant is toxic to cats.
It is also important to understand that essential oils come in a variety of grades all the way from the scent only ones found in candles and wall diffusers all the way up to high quality therapeutic grade. In this case the higher the concentration the worse it is going to be fore your cat. If you're uncertain whether an oil is toxic to your cat or no then the best thing to do is to not diffuse it.
The best thing to do when you wish to diffuse oils and you have a cat is to give them a place to go that is oil free. Your cat should already have a space in your home where they can go to get away from you, other pets, or any stimulus they find displeasing in your home. Never diffuse oils in an enclosed room with no escape for your cat. If your cat sleeps in bed with you at night and you want to diffuse oils then leave the door open. We like to diffuse lavender to go to sleep at times but lavender is displeasing and possibly mildly toxic to cats and is even suggested as a cat repellent.
If you ever notice your cat pacing, panting, and looking disoriented while you are diffusing oils in their presences cease immediately and get your cat to fresh air. With our cat we never diffuse any oil multiple nights in a row. The oils that are mildly toxic to cats, like lavender, are toxic in a way that alcohol is toxic to us. We can't process it and it has an adverse effect on our bodies but our bodies will heal with time. This is also why appearing drunk is one of the signs that your cat has come in contact with a toxic substance.
The best way to know if you should diffuse an oil around your cat is to research and see what plants are toxic to cats and then diffuse none of those oils, but it is important to always be mindful of your cat when diffusing any oil. Follow the steps of never diffusing in an enclosed space with your cat where they can't escape and to stop diffusing any oil immediately and get them to fresh air if they show signs of poisoning.