Eucalyptus is toxic to cats. If your cat has eaten some, call a veterinarian. Eucalyptus is most dangerous when its extracted as an essential oil, although the plant also poses a threat. Despite their efficacy as natural flea and mite repellents, so-called "pet-safe" eucalyptus products are still likely poisonous to cats.
Eucalyptus is a genus of trees and shrubs, mostly native to Australia. It grows in some parts of the United States -- particularly California, where it's considered an invasive species.
Koala bears can, infamously, munch on large quantities of it without ill effect, but your cat cannot. The issue is eucalyptol, the essential oil of eucalyptus, which is a powerful disinfectant.
The risk of cat poisoning is higher in refined eucalyptus products, particularly extracts or essential oils, but also dried variants. Oral exposure or ingestion is the most dangerous. Eucalyptus is also toxic to dogs and horses.
Although it's unequivocally toxic to cats, eucalyptus is sometimes marketed as a pet-safe, natural flea and tick repellant. North Carolina-based Apothecary Herbs Shop, among others, markets cat and dog collars and shampoos made with eucalyptus.
Veterinarian Nada G. Robinson cautions against the use of eucalyptus in such products because of the potential for ingestion or absorption. Even some essential oil advocates, like the people at Experience-Essential-Oils.com, warn not to use eucalyptus with cats or, if you chose to, to do so with "extreme caution."
What to Watch For
Eucalyptus can cause salivation, vomiting, diarrhea, depression and weakness in cats, according to the American Society for the Prevention of Cruelty to Animals. The ASPCA recommends calling your veterinarian or a pet medical emergency hotline for treatment advice.
It's noteworthy that eucalyptus contains phenols, a particular class of chemical compounds that cats can't process. While these may not cause acute issues, their buildup leads to serious conditions, some of which aren't apparent until advanced stages.
Despite its toxicity, some people recommend using eucalyptus -- more specifically its essential oil -- to repel cats. "Soak pieces of cloth or cotton balls in ... (this and similar) substances and place them where you don't want your cat to go," states an article about cat behavior from Maddie's Shelter Medicine Program at Cornell University. Ron Smith, horticulturist professor at North Dakota State University, recommends spraying garden entrances with eucalyptus oil to similar effect.
Given the risks involved, this is not advised.
- eucalyptus tree trunk image by Alison Bowden from Fotolia.com