Unfortunately, I’ve had a few conversations with friends recently about substances toxic to cats. One general rule of thumb – if you don’t know for a fact that something is NOT toxic to cats – assume it is!
Sadly, some of the poisoning cases I’ve heard of had to do with plants. People don’t always think about the plants they bring into their home and whether they’re safe for their feline friends. Lilies are an example – I received a beautiful bouquet of flowers a while back, but they contained lilies. Lilies are EXTREMELY poisonous to cats! In my case, I have two cats at present and both are elderly and don’t jump much – so I was able to put the bouquet up on a small shelf above the kitchen sink so I could enjoy them but they were no danger to my furry companions. My neighbor takes his cat into his back yard, supervised – and I cringe knowing he has Day Lilies growing there.
The ASPCA has a list of plants, and whether they are toxic or non-toxic on their site here:
http://www.aspca.org/Pet-care/poison-control/Plants.aspx
Another substance often overlooked is essential oils. Essential oils can be very dangerous for cats. Ironically, many switch to “natural” cleansers in an effort to avoid chemicals around their pets – but these natural cleansers often contain essential oils which can be just as dangerous, maybe more so. For example, there have been cases such as this reported of cats poisoned with Pine-Sol. The culprit is believed not to be “chemicals” but the pine oil used in the cleanser. With ANY cleanser, I use caution around my cats and rinse thoroughly.
Similarly, my mother’s home always smells lovely due to her many fragrance diffusers. I love the scent, but these diffusers (and potpourri in general) often contain essential oils as well. I opt to have a single scented candle in my bathroom in a spot the cats cannot reach, which I burn when I’m home to supervise. Two good articles on the subject:
http://www.aspca.org/Pet-care/ask-the-expert/ask-the-expert-poison-control/reed-diffusers
In this toxicology brief on most common poisonings of cats, lilies ranked fifth and liquid potpourri ranked sixth.
http://veterinarymedicine.dvm360.com/vetmed/article/articleDetail.jsp?id=334605
Seventh and eighth most common poisonings were over-the-counter medications. I never give over-the-counter medication to my cats unless my veterinarian has advised me to do so. I cringe when I hear people say they’ve given baby aspirin to their cat. A small dose infrequently may be fine, but PLEASE check with your veterinarian! While giving 1/4 of a baby aspiring every three or four days may be okay, giving a dose day for a few days in a row could cause irreparable harm. Cats do not metabolize non-steroidal anti-inflammatory drugs well, given their unique system.
Some additional articles on common household items toxic to cats:
http://purebredcatbreedrescue.org/household_and_holiday_hazards.htm
http://www.aspca.org/Pet-care/poison-control/a-poison-safe-home
Update 7/29/2014:
http://healthypets.mercola.com/sites/healthypets/archive/2014/07/26/pets-tea-tree-oil.aspx
Update 1/16/2018:
http://www.littlebigcat.com/health/aromatherapy-and-essential-oils-for-pets/
https://vcahospitals.com/know-your-pet/essential-oil-and-liquid-potpourri-poisoning-in-dogs