Can I add a fragrance oil or flavour oil to this formulation?

Probably! Here are some things to consider:

Which one?

Fragrance oils and flavour oils are different, and have different uses/purposes. Fragrance oils are used for body products except for lip products, and flavour oils are for lip products. Do not use fragrance oil in lip products. You can use flavour oils in other body products, but I never choose to.

How much?

Fragrance oils are a lot more potent than essential oils, and I usually find that 0.1–0.5% is more than enough to scent a finished product. That said, make sure you are paying attention to the documentation for your specific fragrance oil. Your supplier should list maximum allowable values for a variety of leave-on, rinse-off, and off-body products (like candles). Click here for an example. Some fragrance oils are formulated for candle use and will have a very low leave-on usage rate (or may not be allowed for on-skin use at all), while others are designed for the skin and will have a leave-on usage rate that is many times higher than you’d ever want to use (as in the linked example—72% in body lotion! 😳 That’s strong enough that your neighbours in your apartment building would probably be able to smell your lotion through the ventilation, ha).

For soap: the general rule of thumb is 30g (1.06oz) fragrance or essential oil per 500g (~1lb) of oils, but I find that’s a lot of fragrance and usually use closer to 20g per 500g. Make sure you are paying attention to the maximum values supplied by your supplier as well—those take priority.

How do I make room for it in the formulation?

If it’s a lotion, reduce the water by the same amount (using 0.1% fragrance? Reduce the water by 0.1%). If it’s an anhydrous product, reduce the most-used carrier oil by that amount.

For soap: if your soap was previously unscented you don’t need to remove anything from your soap to make room for fragrance oil.

Want to see the formulation adjustment in action?

Watch this video

Other considerations

  • Tread very carefully with eye products; I usually prefer to scent them with hydrosols if I scent them at all.
  • Surfactant products can behave very differently with different fragrance oils and essential oils. Check out this cool blog post from Botanical Formulations and this experiment I did to get an idea of all the things that can change! There are a ton of variables here—the surfactants, the thickener(s), and all the chemical constituents in your fragrance oil, so isolating the issue can be very challenging (but fun!).
  • If it’s a soap, make sure you’re reading up on how your specific fragrance oil performs in soap. Does it accelerate trace or cause soap to seize? Does it contain vanillin, which will result in browning over time?

Posted in: Troubleshooting & Adjusting