Will steaming fresh eucalyptus branches in my shower harm my cats?

There is a lot of information on the Internet about how toxic eucalyptus is to cats. As it happens it is also toxic to people if sufficient quantity is ingested. Swallowing 10 mL of eucalyptus oil caused a six-year-old boy to go into eight episodes of tonic-clonic convulsions from which he recovered with treatment. 

Eucalyptus shower. Image: The Chic Site.

The toxic symptoms are rapid onset and if an adult ingested 30 mL it would kill them. So, this is a very toxic product in certain dosages. I can't find out right now why it is toxic. Eucalyptus oil is used to clear the sinuses. In showers people hang up eucalyptus leaves and the steam gets into them which helps to make breathing easier if you have sinusitis.

The problem is that cats sometimes come into bathrooms especially if they are wild cat hybrids (they like water). My standard, tabby, moggy rescue cat comes up to the shower when I'm showering. Cats can be interested in the activity especially those who follow their human companion around the home. And if you've got eucalyptus oil mixed up with steam in the bathroom some of it could be deposited on the cat's fur from where it could be licked off when the cat grooms himself.

The obvious point is that a cat caregiver does not want to expose their cat to any risk particularly so when the event that might present the risk to their cat is entirely in their control. If a cat owner harms their cat or even kills their cat because they had a shower with eucalyptus leaves it would be a gross act of negligence. In fact, it would be quite possibly a criminal matter. It wouldn't get to the criminal courts because no one will be bothered about it (except the owner) but on a strict analysis it probably would be a crime. It would be that bad and stupid.

Associated: Is orange oil safe for cats?

To put it another way, you don't want to take the risk unless you can be absolutely sure that your cat won't come into the bathroom either during or after you've had the eucalyptus oil shower. And that might be almost impossible to guarantee because there will be water droplets all over the bathroom well after you left it. These droplets may contain eucalyptus oil. I don't know. Perhaps you are going to tell me that there's no chance that this would happen. But this is about risk and minimising it. The first duty of a cat caregiver is their cat's safety.

The info about toxicity to humans comes from a study: Eucalyptus Oil Poisoning by K. Jagadish Kumar, Sandeep Sonnathi, C. Anitha, and M. Santhoshkumar.