Tea tree oil can be poisonous to cats, especially if the oil is applied without first being diluted, or if the dose is too high. Many veterinarians and other pet care experts recommend not using tea tree oil for cats, even though it has been considered a safe and effective remedy for some feline complaints in the past. Tea tree oil is one of several essential oils, such as peppermint oil, considered toxic to these animals. Flea shampoos for cats often contain small doses of tea tree oil, but many veterinarians advise that these shampoos should be purchased from reputable manufacturers and should bear clearly defined dosage information on the packaging. Cats can easily absorb tea tree oil through the skin, and can also be poisoned by breathing its fumes or by swallowing the oil.
Small doses of tea tree oil, very carefully applied, may not cause immediate or long-term damage to the cat's health. For the average cat, a deadly dose would be somewhere between 1.5 teaspoons (7.4 milliliters) and 3 teaspoons (14.8 milliliters). A safe dose would be about five drops (0.4 milliliters), mixed with 1 teaspoon (4.8 milliliters) of vegetable or olive oil. The mixture should typically be applied to the cat's skin, avoiding the eyes, nose, and mouth.
Cats are generally considered vulnerable to essential oil toxicity because their livers cannot usually metabolize the compounds found in these oils. Some believe that tea tree oil poisoning could occur even when small doses are applied to the skin, since the toxic compounds in the oil can build up in the liver over time. Some of these compounds include camphene, linalool, alpha-terpinene, and terpinolene. Large amounts of these chemicals can cause liver damage and even death in cats, and there is little that can be done for this type of poisoning.
Manufacturers of tea tree oil products for cats typically warn that essential oil doses should be kept very low to avoid problems. Veterinarians and manufacturers alike usually warn against the application of pure tea tree oil to a cat's skin, since it will typically be absorbed easily. Experts also advise against giving a cat tea tree oil orally. Some experts are concerned about the ill effects of inhaling tea tree oil as well, and warn that cats should generally never be exposed to the pure oil.