The growing popularity of essential oils might create problems for pet owners. Essential oils are volatile organic constituents of plants, and while they have many beneficial uses for humans, they can be toxic and harmful to pets, and particular cats.

The oils are rapidly absorbed both orally and through the skin, and are metabolized through the liver. Cats lack the enzyme UDP-glucoronosyltransferase in their liver, and have problems metabolizing certain toxins, such as essential oils. They are also very sensitive to phenols and phenolic compounds, which can be found in some of the oils. The higher the concentration, the higher the risk

Previously, the use of essential oils, while still containing toxic substances to pets, were not as harmful. This is down to how they were used; like in candles, as perfumes, liquid potpourri products. They would also be used in passive diffusers. Passive diffusers work by evaporating the oil into the air to produce a pleasant smell. Types of passive diffusers include reed diffusers (where the reeds soak up the oil to then disperse it into the surrounding air), heat diffusers (like plug-in/electric diffusers, candle burners or table top warmers) non-motorized diffusers, like necklace pendants or bracelets. Another one is the motorized diffuser that use a fan to blow air through a media soaked in an essential oil.

The main hazard of the passive oil diffuser is respiratory irritation. Inhalation of such irritants may cause cats to develop a watery nose and/or eyes, nausea leading to drooling and/or vomiting. If a cat has difficulty breathing, it will need to be immediately removed away from the diffuser, and in to fresh air. If the animal does not recover quickly after being taken away from the essential oil, it is vital that it is brought to the vet immediately.

However, these days active diffusers have come on the market and they work by using steam to push the oils into the air. The oil does not evaporate like with passive diffusers, but is dispersed by steam and will contain tiny droplets of the oil. These droplets will then come in contact with a pet’s fur or skin, and may be ingested when the cat or dog grooms itself. Nebulizing and ultrasonic diffusers both fall in to this group.

It is also important to note that both cats and dogs have an enhanced sense of smell compared to humans, so essential oils may be overwhelming for them.

Oils harmful to dogs include
Clove
Garlic
Juniper
Rosemary
Tea Tree
Thyme
Wintergreen

Oils harmful to cats include
Cassia
Cinnamon
Citrus
Clove
Eucalyptus
Lemon
Lavender
Peppermint
Spruce
Tea Tree
Thyme
Any other oils containing phenols

Even when avoiding these harmful oils and use safer ones instead, it is important to observe your pet closely. Does it seem to be in distress? Remove the oil and anything that might have come in contact with it (like bedding for instance), and make sure the animal has lots of fresh water. If the animal does not recover shortly afterwards, bring it to the vet immediately.