How Concentration Sets Your Fragrance Allergen Triggers

Everyone gets hung up on which allergens are on the list. Fair enough, they matter. But the question that actually decides whether you have to declare anything at all is a math question, not a chemistry question: what's the finished concentration of that allergen in your product, and is your product leave-on or rinse-off.

The two thresholds, side by side

Canada's disclosure rule sets different bars depending on how long the product sits on skin:

• Leave-on products: disclosure required above 0.001%, which is 10 parts per million
• Rinse-off products: disclosure required above 0.01%, which is 100 parts per million

That's a tenfold difference, and it exists because a leave-on product, a moisturizer or a perfume, keeps the allergen in contact with skin far longer than something you wash off in the shower. The logic tracks with how allergic sensitization actually works, longer contact time raises exposure risk, so the bar for declaring is lower.

Why this becomes a concentration exercise fast

Nobody adds "0.003% linalool" directly to a formula. What actually happens is you add an essential oil or a fragrance blend at some percentage of your total formula, and that oil itself contains the allergen at some percentage of itself. To find out whether you've crossed the disclosure threshold, you multiply the two.

Take lavender essential oil, which naturally contains linalool as one of its major constituents. If your lavender oil is roughly 30% linalool by composition, and you're using that oil at 1% in a leave-on lotion, the linalool alone lands at:

0.30 × 0.01 = 0.003, or 0.3%

That's dramatically above the 0.001% leave-on threshold, so it needs to be declared. Now compare a rinse-off shampoo using the same lavender oil at the same 1% usage rate. The linalune concentration in the finished product is identical, 0.3%, but here it's being checked against the rinse-off threshold of 0.01%. Still well above it, still needs declaring. The math is the same, only the bar moves.

Where the numbers get tighter

The interesting cases aren't the ones with a full percent of essential oil. They're the trace ones, a fragrance oil used at 0.1% for a subtle scent note, where a formulator might assume the allergen content is too small to matter. Run the same multiplication: if that fragrance oil is 5% geraniol by composition, and you're using it at 0.1%,

0.05 × 0.001 = 0.00005, or 0.005%

In a leave-on product, that's still above the 0.001% threshold and needs declaring. In a rinse-off product, it falls under the 0.01% threshold and does not. Same trace-level fragrance, two different outcomes, purely because of product category.

A reference table for the two regimes

Scenario	Finished allergen %	Leave-on (0.001% bar)	Rinse-off (0.01% bar)
1% lavender oil, 30% linalool	0.30%	Declare	Declare
0.1% fragrance oil, 5% geraniol	0.005%	Declare	No declaration
0.05% fragrance oil, 2% coumarin	0.001%	Borderline, declare	No declaration

Timing matters here too

List 1, the original fragrance allergen set, becomes mandatory on the CNF and the label in Canada on April 12, 2026. List 2, an expanded set aligned with international lists, follows on August 1, 2026. If you're formulating now, it's worth running this concentration math against both lists rather than just the one currently in force, since a product launching close to the second date will need to already account for the wider allergen set.

Doing the math once, correctly

The practical habit worth building is running this multiplication for every fragrance component, every essential oil, every "natural fragrance" blend in your formula, rather than eyeballing whether a scent feels strong. Common allergens like limonene, linalool, citronellol, geraniol, eugenol, and coumarin show up naturally across a wide range of essential oils, often in combination, so a single "fragrance" line in your formula can actually represent several allergens each needing their own threshold check.

Cosmetic Comply carries these calculations through automatically, expanding fragrance and essential oil blends into their known constituent allergens, applying the correct leave-on or rinse-off threshold, and flagging what needs to appear on your CNF and label before you file. If you're the type who'd rather trust the multiplication than trust a gut feeling about how strong a scent smells, that's the safer way to work anyway.