Calculating Allergens When You Blend Multiple Oils

Say your body butter has lavender oil, bergamot oil, and a touch of ylang ylang, each added for a reason, scent layering, a specific note you're chasing. Individually, none of them seem like much. But all three of those oils naturally contain linalool. If you calculate linalool from just one of them and stop there, you've undercounted what's actually in the jar.

This is the part of allergen math that catches experienced formulators off guard, not beginners. Beginners tend to use one or two oils and the math is simple. It's the layered, multi-oil blends, the kind that make a fragrance interesting, where allergens sneak past a quick check.

Why you have to sum across sources

Fragrance allergens like Limonene, Linalool, Citronellol, Geraniol, and Eugenol occur naturally across a wide range of essential oils. Lavender, bergamot, and ylang ylang can each carry linalool, just at different percentages. The disclosure requirement isn't about any single ingredient you added, it's about the total concentration of that specific allergen molecule sitting in your finished product, no matter how many places it came from.

Under the incoming Canadian disclosure requirements, that total matters because it's compared against the actual thresholds: above 0.001% (10 ppm) in leave-on products and above 0.01% (100 ppm) in rinse-off products. A body butter is leave-on. That's a very low bar, low enough that several small contributions from different oils can add up to something that needs disclosing even when each individual oil's contribution looked negligible.

Working through the math

Here's the general shape of the calculation for one allergen across multiple sources:

1. Find the approximate percentage of the allergen within each essential oil (supplier documentation or a certificate of analysis is the right source for this, not a general estimate)
2. Multiply that percentage by the use level of that oil in your finished formula
3. Repeat for every oil in the formula that contains the same allergen
4. Add all of those contributions together
5. Compare the summed total against the leave-on or rinse-off threshold, whichever applies to your product

A simplified example, using illustrative numbers rather than real supplier data:

Oil	Use level in formula	Approx. linalool content in oil	Linalool contributed
Lavender oil	0.8%	30%	0.24%
Bergamot oil	0.3%	8%	0.024%
Ylang ylang oil	0.2%	5%	0.01%
Total linalool			0.274%

That total, 0.274% in this illustration, is what gets compared to the disclosure threshold and, once it clears the threshold, listed as Linalool by its INCI name on the CNF and the label, not broken back out by which oil it came from.

Common mistakes

Checking only the "main" fragrance oil. If your formula has a primary scent oil plus a couple of smaller supporting oils, it's tempting to only check the dominant one. The supporting oils often still push a shared allergen over the line.

Using generic allergen percentages instead of supplier-specific ones. Essential oil composition varies by source, growing conditions, and distillation batch. A certificate of analysis from your actual supplier is more reliable than a textbook average.

Forgetting that a fragrance blend you buy pre-made is itself a source. If you use a supplier's proprietary fragrance blend rather than raw essential oils, that blend likely has its own allergen content documented, and it needs to be included in the same summed total alongside any essential oils you add separately.

Not rechecking after a formula tweak. Adding even a small amount of a new oil, or adjusting a percentage during a reformulation, changes the sum. It's worth rerunning the calculation any time inputs shift, not just at initial launch.

Getting ahead of the 2026 deadlines

List 1 allergens become mandatory on the CNF and label on April 12, 2026, and List 2 follows on August 1, 2026. If you're formulating with essential oil blends now, this is the moment to build the summed calculation into your process rather than trying to reconstruct it under deadline pressure later.

This kind of multi-source summing is exactly the tedious, error-prone math that Cosmetic Comply automates when you submit your ingredient list, since it already expands supplier blends into their components and carries percentages through, then totals shared allergens across every contributing oil before checking them against the leave-on or rinse-off threshold that applies to your product.