Blending Fragrance Oils: How to Check the IFRA Limit

Each fragrance oil comes with its own IFRA certificate, so a blend has no single certificate unless someone writes one for it. To check a blend yourself, work out how much of each oil ends up in the finished candle and compare it with that oil's own Category 12 limit. For a safe-side check across the whole blend, divide each oil's share by its limit, add the results, and keep the total at or under 1. That sum is my own arithmetic, not an IFRA rule. I am a candle maker, not a lawyer, so this is a way to check your numbers, not legal advice.

Why does a blend need its own check?

CandleScience puts it this way: "Each and every fragrance has its own certificate confirming compliance with IFRA's standards." IFRA's guidance says a certificate "confirms that a specific fragrance mixture up to a certain concentration can be used in a specified consumer product" up to a named Amendment. Your two oils are two separate mixtures, each with its own limit.

IFRA states those limits as a concentration in the finished product, "weight-per-weight percent" unless it says otherwise. So the number to compare is the share of each oil in the finished candle, not the share in the oil bottle and not the percent of the wax.

I searched the text of IFRA's 51st Amendment guidance for the word "blend" and found no hits, so I found no IFRA method for adding up the limits of two oils. The guidance does say suppliers may add, on a voluntary basis, the levels of restricted ingredients in the mixture. A certificate does not have to show them, so you cannot see whether two of your oils share one.

What are the steps?

1. Start from the jar's total fill (wax plus oil) and your fragrance load, counted on the wax.
2. Wax = fill / (1 + load). Total oil = wax x load.
3. Split the oil by your blend percents. Our blending guide covers choosing the split for scent.
4. Each oil's share of the candle = that oil's weight / the fill x 100.
5. Compare each share with that oil's Category 12 limit on its certificate. Candles are in Category 12 (CandleScience: "Air care not intended for direct skin contact"). For reading the certificate, see How to read an IFRA certificate.
6. Safe-side check: add share / limit for every oil. At or under 1 passes.

Why step 6 leans safe: two oils might both contain the same restricted ingredient, and the certificates do not have to show it. Their limits then draw on one shared allowance, and adding share / limit is a way to count that. When the oils are limited by different ingredients, the sum asks for more than the rules need. That is my reasoning, so if you sell the blend widely, ask your supplier whether they can issue a certificate for the exact blend.

Worked example: a 10 oz jar, two oils

These numbers are made up. Fill 10 oz, load 8 percent of the wax weight. Oil A has a Category 12 limit of 5.00 percent. Oil B has a limit of 100 (the certificate sets no real cap).

• Wax = 10 / 1.08 = 9.26 oz
• Total oil = 9.26 x 0.08 = 0.74 oz, which is 7.41 percent of the candle

Blend 50/50. Each oil is 0.37 oz, or 3.70 percent of the candle.

• Oil A: 3.70 is under 5.00, so it passes alone.
• Safe-side sum: 3.70 / 5.00 + 3.70 / 100 = 0.74 + 0.04 = 0.78. Under 1, so it passes.

Blend 70/30. Oil A is 0.52 oz, or 5.19 percent of the candle. Oil B is 0.22 oz, or 2.22 percent.

• Oil A: 5.19 is over 5.00. It fails alone.
• Safe-side sum: 5.19 / 5.00 + 2.22 / 100 = 1.04 + 0.02 = 1.06. Over 1.

Two fixes, both computed the same way:

• Keep 70/30 and drop the load to 7 percent of the wax. Wax = 10 / 1.07 = 9.35 oz, oil = 0.65 oz. Oil A is 4.58 percent and oil B is 1.96 percent of the candle. Sum = 0.92 + 0.02 = 0.94. It passes.
• Keep the 8 percent load and move to 60/40. Oil A is 4.44 percent and oil B is 2.96 percent. Sum = 0.89 + 0.03 = 0.92. It passes.

Whichever you pick, your wax has its own maximum load, which is a separate check. See which limit wins.

What about an essential oil in the blend?

Essential oils are handled differently from a supplier's fragrance oil. See our guide on essential oils and IFRA before you count one in a blend.

Common mistakes

• Checking the whole blend against one oil's limit, usually the higher one. Each oil has its own limit and its own share of the candle.
• Comparing the percent of the wax with the limit. The limit is on the finished product, so convert first. Fragrance load: percent of wax or total shows the two methods.
• Using each oil's full load. Three oils at 8 percent each is not an 8 percent load. The total oil is 8 percent of the wax.
• Mixing certificates from different Amendments without looking. Each one should name its Amendment, so check the date on each.
• Treating a certificate limit as a target. CandleScience says the maximum "is not a recommendation for how much you should use for the best end results."

Questions

Does a limit of 100 mean I can ignore that oil?

For the sum, an oil with a limit of 100 adds almost nothing, as the 0.04 above shows. But the number only covers the IFRA ingredient rules. It does not cover your wax's max load, and it does not replace a safety assessment, which IFRA's guidance says a certificate does not do.

Do I need a new check if I change the blend?

Yes. The shares change, so the numbers change. In the example, moving from 50/50 to 70/30 turned a pass into a fail.