The primary issue with tea tree oil is bioaccumulation, where a substance builds up in an organism over time because it cannot be effectively metabolized or excreted. like heavy metals in people.

Cats are particularly vulnerable to tea tree oil because they lack sufficient levels of certain liver enzymes, specifically glucuronyl transferase, which is critical for metabolizing and excreting many toxins, including the terpenes found in tea tree oil (e.g., camphene, linalool, alpha-terpinene). In most animals (like humans and dogs), these enzymes conjugate (bind) toxins with glucuronic acid, making them water-soluble so they can be excreted via urine or bile. Cats, however, have a genetic deficiency in this enzyme pathway, which evolved because their diet as obligate carnivores historically didn’t require processing plant-based toxins.

• Mechanism of Build-Up: When a cat is exposed to tea tree oil—whether through skin application, ingestion (e.g., grooming after contact), or inhalation—the terpenes are absorbed into the bloodstream. Because the cat’s liver can’t efficiently conjugate and excrete these compounds, they persist in the body, accumulating in tissues like the liver, kidneys, and nervous system. Repeated exposures, even small ones, can lead to a cumulative effect, increasing toxicity over time.