Base Formula Guide

Formulas for Home Fragrance

What else is in a fragrance besides the scent?

Home fragrance is never just scent molecules. It’s also what carries the scent and how it gets into the room. For example:

• Scented candles are wax, wax additives, what the wick is made of, and molecules created by burning.

• Scented room sprays contain water, surfactants, and preservatives

• Incense is scented powder blended with resin, bamboo stick, and molecules created by burning.

Why do fragrances have surfactants?

Oil and water don’t mix, so most water-based fragrances like room sprays, linen sprays, and diffusers need a surfactant (also called a solubilizer) to hold an oil-based fragrance in the water. Common ones are polysorbate 20, polysorbate 80, and PEG-40 hydrogenated castor oil. These are ethoxylated ingredients, which means they can carry trace 1,4-dioxane and ethylene oxide from manufacturing and they are being restricted in some states.

Do fragrances contain preservatives?

Water-based products like room sprays and water-based diffusers do need preservatives, however, so often contain isothiazolinones (like methylisothiazolinone), phenoxyethanol, or sodium benzoate. Methylisothiazolinone is a well-documented skin allergen so the EU and Canada have restricted it, though the US hasn’t.

Fragrance oils don’t need preservatives because bacteria and mold don’t grow in oil. Many fragrance oils do contain antioxidants, like BHT or tocopherol (vitamin E), to keep the scent from oxidizing.

Search any of these preservatives for what they do and where they’re restricted or banned on my Check a Fragrance page.

What is a dispersal method?

This is a fancy way of describing how the scent gets thrown into your room. It can happen through simple evaporation, forced out as little tiny particles like happens in nebulization, it can be burned or smoldered, like a candle or incense. It’s an important part of how healthy a fragrance is because burning anything in your home produces soot, nebulizers can create ultrafine particles, and simple evaporation adds nothing harmful.

What is evaporation?

Evaporation is when a liquid scent drifts into the air on its own over time, similar to how a puddle evaporates on a sunny day. This is how reed diffusers, scented gels and beads, sachets, and potpourri work. It’s also what happens after you spritz a scent from a regular pump or trigger bottle: the water evaporates into the air.

Fan diffusers speed up the process. They blow air across a pad soaked in scent. Think of using a small fan to help the scent evaporate faster.

Evaporation adds the fewest extra things to your air. There’s no flame or propellant-forced mist, so what you breathe is mostly the scent molecules themselves. That doesn’t make it risk-free: scent molecules still react with ozone indoors no matter how they get into the air (more on that in the scent section above).

What is nebulized or ultrasonic diffusion?

Ultrasonic and nebulizing diffusers work differently from evaporation, including evaporative fan-based diffusers. They push tiny droplets into the air.

Ultrasonic diffusers hold water with a few drops of oil. A plate vibrates at a high frequency and breaks the water into a fine mist that carries the oil with it. Anything else in the water goes airborne too. The EPA notes these devices are very efficient at releasing the minerals in tap water into the air, and a Virginia Tech study found tap water in an ultrasonic humidifier raised room particle counts nearly 13 times, while distilled water raised them only slightly. That research was on humidifiers, which use the same technology. If you use an ultrasonic diffuser, use distilled water.

Nebulizers use no water at all. They turn undiluted fragrance oil into an aerosol, so you get a more concentrated output.

Both produce small airborne particles. Chamber studies have measured particles in the 10–100 nanometer range from ultrasonic diffusers, which is small enough to reach deep into the lungs. The research here is early, and the health effects of routinely breathing nanoparticles from diffusers aren’t well characterized. I think caution is reasonable.

What are aerosols?

Technically, an aerosol is any suspension of fine liquid or solid particles in air, so every spray makes one. But in normal everyday use, “aerosol” means a pressurized can that uses gas to propel the contents out as a very fine mist. Think spray paint, or canned room sprays like Febreze Air.

The difference from pressurized bottles and regular bottles is how long the particles stay in the air. In a chamber study of cleaning sprays, particles from pressurized cans took about twice as long to settle as particles from regular spray bottles. More time in the air means more time to breathe it in, so it’s more important that the scent is safe.

What are propellants?

Propellants are the compressed gases in aerosol cans that force the scent out as a powerful mist. In the “olden days,” this gas was CFCs, or chlorofluorocarbons. The US banned CFCs as aerosol propellants in 1978 because they damage the ozone layer. Brands mostly switched to hydrocarbon propellants so today that usually means propane, butane, and isobutane, or compressed gases like nitrogen or CO2. Since propellants are released into the air along with the product, what they are can impact your indoor air quality. Even if they come out in very small quantities with each spray, if you use a spray very often, it can potentially add up.

What is the difference between nitrogen and other gas propellants?

Hydrocarbon propellants like propane, butane, and isobutane are the most common in consumer aerosols. They’re flammable and add to your indoor VOC load, though a single spray delivers a small amount.

The bigger concern is contamination. Starting in 2021, an independent lab found benzene, a known human carcinogen, in many personal care aerosols. The FDA pointed to the propellant isobutane as one possible source. Those were deodorants, dry shampoos, and sunscreens, not air fresheners. But they show the broader problem: aerosols contain several ingredients besides the scent, and full disclosure is rare.

Nitrogen is the most inert option because it doesn’t react with much. It’s less common because it doesn’t keep pressure as steady as the can empties. If a safety data sheet lists nitrogen as the propellant, that’s the better choice among aerosols. Skipping aerosols for home fragrance altogether is the simpler move when alternatives exist.

And yes, it’s true that one spray won’t hurt you on its own. But, we’re constantly exposed to poor air quality, so if you can make this change without added stress, I think it’s a good idea.