Hotel scent. Your home. $10/month.

Take this seriously – cats process these compounds differently from us, and several common oils including tea tree, eucalyptus, peppermint, citrus and cinnamon are considered unsafe around them. The safest approach is not to diffuse in rooms your cat can access, and never to let oil touch their fur or skin. If you do diffuse elsewhere, keep the door shut, run it briefly, ventilate afterwards, and make sure the cat can always leave the room. Your vet is the right person to ask about your particular animal – and if your cat drools, vomits, seems wobbly or is breathing oddly, stop and ring them.

Birds are the most sensitive of all – their respiratory systems are delicate enough that diffusing in a room with a bird isn't advisable at all. Dogs tolerate more than cats but still shouldn't be exposed to concentrated oils, and tea tree in particular is unsafe for them. As with cats, never apply anything to their coat, and check with your vet before you start.

Far less than most people do – a few drops in total, not a few drops of each on top of each other. Run the diffuser for half an hour and then turn it off rather than leaving it going all day, keep the room ventilated, and start lower than you think. If anyone has asthma or reacts to scent, start with the smallest amount or skip diffusion entirely.

The label should say it's pure essential oil and give the botanical name in Latin rather than just 'lavender'. Anything described as fragrance oil or perfume oil is synthetic and behaves differently. Price is a rough guide too – some oils are expensive to produce, so a whole range at one low price is a sign to look closer.

That's the enjoyable part. Keep it to three oils, a couple of drops of each, and include one from each note so it has some depth rather than sitting flat. Make a note of what you used – the blend you stumble into and can't reproduce is a genuine frustration.