If you've seen those little devices producing a gentle, fragrant mist and wondered what exactly they are - you're not alone. So, what is a diffuser? An oil diffuser is one of the simplest ways to fill your home with beautiful scent while enjoying the calming ritual of aromatherapy.
In short, an oil diffuser is a device that disperses essential oils into the air as a fine mist. Rather than burning oils or using heat (which can alter their scent), most modern diffusers use ultrasonic vibrations to break oils and water into microscopic particles that float through your space. The result? A room that smells incredible and, depending on the oils you choose, a lovely shift in the mood and atmosphere of your home.
We've been working with oil diffusers for years at our Wellington studio, testing dozens of models and helping thousands of customers find the right one. Here's everything you need to know about how they work, how to use one, and how to get the most from yours.
How does an oil diffuser work?
The most popular type - the ultrasonic diffuser - works using high-frequency vibrations. Inside the device, a small ceramic disc vibrates at ultrasonic frequencies (too fast for human ears to detect). These vibrations break the water and essential oil mixture into incredibly fine particles, which are then released as a cool, aromatic mist.
Because there's no heat involved, the delicate aromatic compounds in essential oils stay intact - heat can dull the fresh, true scent of an oil, which is why cool-mist diffusing is the aromatherapy favourite.
The mist is so fine that it doesn't feel wet or leave residue. It simply disperses the scent evenly through your room, so you breathe in the aroma gently as you go about your day.
Types of oil diffusers
Not all diffusers work the same way. Here are the main types you'll come across.
Ultrasonic diffusers
The most common, and what most people picture. They use water mixed with a few drops of essential oil, and ultrasonic vibrations create the mist. They're quiet, safe, energy-efficient, and many double as a subtle night light with LED colour options. This is the type we stock at Seven Scents because they offer the best combination of performance, safety and value - browse our ultrasonic oil diffusers to see the range.
Nebulising diffusers
These use pressurised air to atomise pure essential oil - no water required. They deliver a more concentrated scent and are great for larger spaces. The trade-off? They use essential oils faster and tend to be pricier. If you want the strongest possible aroma and don't mind going through oils more quickly, nebulisers are worth considering.
Heat diffusers
These warm essential oils to help them evaporate. They're affordable and simple, but the heat can change the scent of the oils as they warm. Electric heat diffusers are safer than candle-powered versions, but we generally recommend ultrasonic models for the truest aroma.
Evaporative diffusers
These use a small fan to blow air through a pad or filter soaked in essential oil. As air passes over the oil, it evaporates and disperses. They're portable and don't need water, but the scent can be less consistent, as the lighter top notes evaporate first.
Reed diffusers
Technically not "oil diffusers" in the electric sense, but worth a mention. Reed diffusers use wooden sticks that draw fragrance up from a bottle and release scent passively - no power, no mist, just gentle continuous fragrance. Perfect for smaller spaces, or anywhere you want set-and-forget scenting.
Is a diffuser the same as a humidifier?
It's a common mix-up, and the short answer is no. A humidifier is built to add a lot of moisture to the air to raise a room's humidity. A diffuser is built to disperse scent - it releases far less water, just enough to carry the aroma. If your goal is fragrance and atmosphere, you want a diffuser; if you're treating genuinely dry air, you want a humidifier. We've written a full diffuser vs humidifier comparison if you'd like the detail.
How to use an oil diffuser
Using an ultrasonic diffuser is genuinely straightforward. Here's the process.
1. Choose your location
Place your diffuser on a stable, flat surface at least 60cm above the floor so the mist can disperse through the room. A bedside table, shelf or desk works well. Keep it away from the edge where it might get knocked, and near a power point.
2. Fill the water tank
Remove the lid and fill the tank with water to the maximum line - never above it. Most diffusers hold between 100ml and 300ml. We recommend filtered or previously boiled water rather than tap water, as minerals in hard water can build up inside the device over time and affect performance.
3. Add your essential oils
Add 3–10 drops of essential oil depending on your tank size and how strong you want the scent. For a 100ml tank, 3–5 drops is usually plenty; for larger tanks (200–300ml), 5–10 drops works well. Use a single oil or create your own blends - experimenting with combinations is half the fun.
4. Set your preferences
Replace the lid, plug in and switch on. Most models let you adjust the mist (continuous or intermittent), a timer (1, 3 or 6 hours) and LED light colours. Intermittent misting makes your water and oils last longer while still keeping the room fragrant.
5. Enjoy
That's it. Your diffuser runs until the water runs out or the timer stops it. Most quality diffusers have an auto shut-off that turns the device off when the water gets low - an important safety feature.
Can you just use water in a diffuser?
You can run a diffuser with water only - it'll release a gentle cool mist with no scent, which some people like for a whisper of extra moisture. But the whole point of an oil diffuser is the aroma, so you'll get the most from it with a few drops of oil added. Plain water won't harm the device.
How many drops of essential oil should you use?
One of the most common questions we get. It depends on a few things:
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Tank size - smaller tanks (100ml) need fewer drops (3–5); larger tanks (300ml+) can handle more (8–10).
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Room size - a small bedroom needs less than an open-plan living area.
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Personal preference - some love a subtle background scent, others want it more noticeable.
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Oil strength - some oils are naturally stronger. Peppermint and eucalyptus are potent, so a little goes a long way; lavender and citrus oils are softer.
Start with fewer drops and add more if needed. You can always increase the intensity, but you can't easily dial it back once the oils are in the water. If you'd like ready-made combinations, our 15 DIY diffuser blend recipes are a great place to start.
Can you use any oils in a diffuser?
For aromatherapy, use pure essential oils in your diffuser - concentrated plant extracts obtained through steam distillation or cold pressing.
Fragrance oils can also be used if your goal is simply to make your space smell lovely. They don't carry the botanical origins of essential oils, but they're wonderful for home fragrance and come in a much wider variety of scents - including complex blends that don't exist in nature.
What you shouldn't use: cooking oils, carrier oils on their own (like coconut or sweet almond), or anything not designed for diffusing. These can clog your diffuser and won't disperse properly.
Benefits of using an oil diffuser
Why bother with a diffuser at all? Here's what makes them worth having.
A simple aromatherapy ritual
Different oils suit different moods. Lavender is the classic for winding down and a restful bedroom; eucalyptus and peppermint are fresh, cooling and lovely in winter; citrus oils like lemon and orange are bright and uplifting. A diffuser lets you enjoy these scents simply by breathing normally in your own home.
A lovely alternative to candles
We love a good candle, but diffusers have some advantages: no open flame (safer around children and pets), longer-lasting scent from less product, and the ability to run while you sleep or leave the room. Many people use a diffuser as their everyday home fragrance and save candles for special occasions.
Mood and atmosphere
Scent has a powerful effect on how a space feels. A diffuser running with the right oil can make your home feel calmer, fresher, more inviting or more focused - depending on what you choose. It's one of the simplest ways to shift the mood of a room.
A touch of extra moisture
Diffusers aren't humidifiers (they release far less water), but the fine mist does add a tiny amount of moisture to the air. In a very dry room that can feel pleasant - though for genuinely dry air you'll want a dedicated humidifier.
Is it okay to sleep with a diffuser on?
Many people love diffusing a calming scent like lavender at bedtime, and quality diffusers are designed with sleep in mind - quiet operation, a dimmable or off light, and auto shut-off when the water runs low. A few sensible tips: use a timer or intermittent setting rather than running it all night, keep the room ventilated, choose a gentle oil, and keep the diffuser out of reach of children and pets. If anyone in the room has a respiratory condition, or you're diffusing around babies or animals, check with a qualified professional first.
How to clean your oil diffuser
Regular cleaning keeps your diffuser working well and stops oil residue building up.
Quick clean (weekly)
- Unplug the diffuser and empty any remaining water.
- Wipe the inside of the tank with a soft, damp cloth.
- Use a cotton bud to gently clean around the ultrasonic disc (the small ceramic plate at the bottom).
- Wipe dry and refill as normal.
Deep clean (monthly)
- Fill the tank halfway with clean water and add a teaspoon of white vinegar.
- Run the diffuser for 5–10 minutes to let the solution work through the system.
- Empty completely and wipe all surfaces with a cloth dampened with vinegar.
- Rinse with clean water and dry thoroughly before next use.
Avoid harsh chemicals or abrasive materials - they can damage the tank and ultrasonic components.
Troubleshooting common issues
Weak or no mist
First, check the water level - too little water means weak mist. If the tank is full, the ultrasonic disc may have residue buildup, so give it a clean with a cotton bud. Also make sure the diffuser is on a flat surface; tilting can affect the disc's contact with the water.
Scent isn't strong enough
Add more drops. If you've used the same oil for a while, you may be experiencing "nose blindness" - your brain tunes out familiar scents. Switch to a different oil for a few days, then come back to your favourite.
Diffuser won't turn on
Check the power connection and make sure the lid is properly seated - many diffusers won't run if the lid isn't correctly in place. If it still won't work, the unit may need replacing.
Choosing the right diffuser for your space
When selecting a diffuser, consider:
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Room size - larger rooms need a bigger tank or stronger output.
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Run time - for all-day diffusing, look for a larger capacity or an intermittent setting.
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Noise level - ultrasonic diffusers are generally very quiet, but check reviews if you're sensitive to sound.
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Aesthetics - your diffuser will be on display, so choose one that fits your décor.
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Features - a timer, auto shut-off and LED lighting are all worth having.
For a bigger room or office, our guide to the best diffusers for a large room goes deeper, or see our pick of the best oil diffusers in NZ.
Ready to start diffusing?
An oil diffuser is one of the easiest ways to bring a little aromatherapy into everyday life. Whether you're after a calmer bedroom, a fresher-smelling home, or simply a more inviting atmosphere, there's a diffuser and oil combination that'll suit you.
Browse our range of ultrasonic oil diffusers - we've tested and chosen each one for performance, reliability and design - and pair yours with our pure essential oils or fragrance oils to find your favourite scents.
This information is for educational purposes only and isn't medical advice. Essential oils aren't a substitute for professional care. If you're pregnant, breastfeeding, have a health condition, or are using oils around children or pets, check with a qualified healthcare provider or aromatherapist first.
