Safe at home

Start with the part that costs us money

Twelve of the single notes people commonly diffuse appear on the ASPCA's list of essential oils known to cause poisoning in cats: Grapefruit, Sweet Orange, Lemon, Tangerine and Bergamot as citrus oils containing d-limonene, plus Pine Needles, Ylang Ylang, Peppermint, Cinnamon, Clove, Eucalyptus and Tea Tree. The ASPCA's list also includes wintergreen, sweet birch and pennyroyal.

We could have left that off the site. Citrus is the single largest group on the shelf in most homes, and several of them — eucalyptus, peppermint — are exactly what people search for.

Why cats specifically

Cats lack an efficient version of the liver enzyme pathway that breaks these compounds down, so what a person or a dog clears without noticing can accumulate in a cat. The ASPCA describes possible effects from significant exposure as gastrointestinal upset, central nervous system depression and liver damage. Texas A&M's veterinary school has published the same warning specifically about diffusers.

Dogs are less sensitive but not immune, and any animal with existing breathing problems is a reason to skip diffusing altogether rather than to ventilate harder.

Passive and active diffusers are not the same question

This distinction does most of the work:

• Passive — a reed diffuser, or a tealight oil warmer. No droplets of oil leave the device. Unless the oil gets onto an animal's coat or is licked, the main hazard is respiratory irritation.
• Active — ultrasonic and nebulizing diffusers, including ours. These emit actual microdroplets of oil into the air alongside the smell. The droplets are small; they are still oil, and they still land on surfaces and on fur.

So an ultrasonic diffuser in a home with a cat is a different decision from a warmer in the same home, and the honest answer for a cat household is: short runs, in a room the animal can leave, or a note that is not on the list.

The practical rules

1. Diffuse in a room with a door and airflow, never in a closed room an animal cannot leave.
2. Run it for a set period rather than continuously. Half an hour to two hours is enough for a bedroom.
3. Keep bottles capped and out of reach. Ingestion, not inhalation, is the severe case.
4. Never apply oil to an animal's coat or skin.
5. If an animal has asthma or any breathing condition, do not diffuse.
6. If you think an animal has been exposed, call a vet or the ASPCA Animal Poison Control Center on (888) 426-4435.

Babies, children and pregnancy

We are not going to give a confident answer here, because there isn't one. Guidance is inconsistent and the trials are small. What is consistent: nurseries and cots are the wrong place for a diffuser, undiluted oils should never touch a child's skin, and pregnancy is a question for a midwife or doctor, not for a shop.

Open flame is the other risk, and it is the ordinary one

Both our warmers run on a tealight. That makes them a candle, with candle rules: a flat heat-proof surface, nothing above them, nothing flammable within arm's reach, never left burning in an empty room, never lit in a bedroom you intend to sleep in. Keep water in the dish — oil alone will scorch the ceramic and smoke.

Non-electric is not the same as low-risk. It is a different risk, and it is the one that burns houses down rather than the one that upsets a cat.

Read next

• Essential oils and cats — the list in full, which twelve notes are on it, and how to run a diffuser anyway.
• Essential oils and dogs — what the case series actually record, and why the route matters more than the oil.
• Are essential oil diffusers bad for you? — the air-quality research, and the one change that fixes most of it.
• Oil warmer or diffuser: flame or switch — passive against active, and the candle rules.