Not All Fragrance Oils Are Equal: How to Tell a Good One (and Which Can Go in Your Diffuser)

Two bottles can both say "fragrance oil" and be completely different things inside. Here is what separates a good one from a cheap one, and why not every oil can go in every diffuser.

"Fragrance oil" sounds like one thing. It isn't. It is a label that covers everything from a carefully built perfume concentrate to a little scent stretched out with a cheap solvent. Most of the difference is invisible until you use it: one fills a room for weeks, the other fades in days, or clogs your diffuser.

What a fragrance oil actually is

A fragrance oil is a blend of aromatic materials, some natural, some made in a lab, built by a perfumer to smell a certain way and to keep smelling that way. (If you're weighing it against essential oils, we've written about the real difference between the two.)

How cheap oils get cheap

The easiest way to lower the price of a fragrance oil is to dilute it. Many budget oils are cut with a solvent such as dipropylene glycol (DPG) or a carrier like fractionated coconut oil or mineral oil. Nothing is wrong with those ingredients on their own, but:

• You are paying for solvent, not scent. A diluted oil needs more to do the same job.
• In a cold-air diffuser, carrier oils are too thick to atomise and coat the nozzle.
• In a reed diffuser, you can't set the strength properly because you don't know how strong the oil was to begin with.

Five signs of a good fragrance oil

1. It says what's in the bottle. "100% concentrated" or "neat" means undiluted. Vague wording usually means it isn't.
2. It is IFRA-compliant, and the maker can prove it. IFRA sets the safe maximum amount of each fragrance material for each type of product. A serious maker can give you an IFRA certificate and a Safety Data Sheet (SDS) when you ask.
3. It is made for your use. A good maker tells you where the oil belongs (reed diffuser, cold-air diffuser, candle, spray) and where it doesn't.
4. It smells the same from top to bottom of the bottle. Good oils are balanced so the scent doesn't flatten or turn sharp as it evaporates.
5. It is free of the things you don't want. Look for phthalate-free and clear safety guidance.

Why not every oil can go in every diffuser

This is where most people go wrong.

• Cold-air (waterless or nebulizing) diffusers atomise oil exactly as it comes out of the bottle, so they need pure, thin, undiluted fragrance oil. Carrier oils, reed diffuser blends, water-based oils and alcohol perfumes clog the atomiser or dry out its seals.
• Reed diffusers need fragrance mixed into a diffuser base so it can climb the reeds. Neat oil on its own wicks unevenly and can overwhelm a room.
• Ultrasonic (water) diffusers are made for small amounts of oil floating on water; concentrated fragrance oil can be hard on their plastic parts. Always check the maker's instructions.

That's why we keep our ranges separate: Cold-Air Concentrate is 100% concentrated fragrance oil for waterless and cold-air diffusers, and our reed diffuser refills are ready-mixed for reeds only. The concentrate can also become a reed diffuser, if you blend 20 to 25% into our Reed Diffuser Base.

Quick answers

Is a more expensive oil always better? Not always, but a very cheap concentrated oil is almost always diluted.

Can I test an oil before buying a big bottle? Yes. Our Complete Hotel Edit has all six hotel scents as 5 ml samples.

Where can I see the safety documents? Email [email protected] and we'll send the SDS for any of our oils.

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More from the Journal

• Waterless Diffuser Oil: How to Choose One That Won't Clog Your Diffuser — Cold-air and waterless diffusers are fussy about what goes in them. Here is what to look for in the oil, what to never pour in, and how to work out how long a bottle will last.
• IFRA, SDS, Phthalate-Free: What Fragrance Labels Actually Mean — Fragrance labels are full of letters and promises. Some are backed by real documents, some are just marketing. Here is how to tell the difference.
• How Much Fragrance Oil per 100 ml of Reed Diffuser Base? — The most common question from people making their own reed diffusers: how much oil goes in? Here is the ratio, why it's measured by weight, and a gram chart you can use with a kitchen scale.