There is no exact science to diffusing. There’s also no standard recommendation for how long to diffuse your oils. A standard rule of thumb is to diffuse for 15 to 20 minutes, which is more than enough time to saturate a standard-size room with scent molecules. A general best practice is to diffuse roughly 3 to 5 drops of essential oil per 100 mL of water in an ultrasonic diffuser and 5 to 15 drops of essential oil in a nebulizer depending on the note of the oil; however, it’s always best to follow your device’s instructions and experiment with your own amounts. Remember, a little goes a long way.
Nowadays, most diffusers come with a timer setting to help you customize your preferences. But keep in mind there are a number of factors that affect how well diffusion works. First, each essential oil will stay in the air for a different amount of time. Top notes, like peppermint, lavender, and eucalyptus typically evaporate within an hour or two. Middle notes, like rosemary, geranium, and chamomile, often aromatically evaporate within two to four hours. And heavier base notes, like myrrh, cedarwood, and ginger can be detected by olfaction for five or more hours and may even linger for days. Creating balanced synergies can help make a scent last longer or enhance overall therapeutic benefit. For example, combining top notes with complementary base notes helps stabilize the more volatile top note chemicals, making them detectable longer than diffusing just that single note.
The environment also affects diffusion. Room temperature and air circulation can cause molecules to evaporate more or less quickly. For example, warm spaces create greater excitement within bonds of aromatic molecules, which causes them to vanish rapidly. So you may need to add a few extra drops if you’re diffusing in a particularly hot room. Also be wary that any overpowering HVAC system may accelerate spreading the molecules throughout a space. The opposite can also be true; rapid air movement may cause the scent to last for less time.