The 0.001 Percent Leave-On Allergen Trigger Explained

Ten parts per million. That is what 0.001% works out to, and it is the line Health Canada draws for when a fragrance allergen has to show up on your Cosmetic Notification Form and on the label of a leave-on product. If you have been treating fragrance allergens as a "strong essential oil blend" problem, this number is going to surprise you.

Why leave-on gets the strict threshold

Leave-on products stay on skin. A lotion, a facial serum, a leave-in conditioner, a lip balm. There is no rinse step to carry residue away, so contact time and total exposure are both higher than they are for something you wash off in thirty seconds. Health Canada's logic tracks the same reasoning international bodies use: the longer an allergen sits on skin, the lower the concentration needs to be before it becomes a genuine sensitization risk for someone who already reacts to it.

Rinse-off products get a looser number, 0.01% (100 ppm), ten times higher. Same allergen list, same disclosure obligation, just a different bar depending on how the product is used.

What ten parts per million looks like in a real formula

Ten ppm sounds abstract until you run it through an actual recipe. Say you are making a body lotion at 500 grams batch size and you add 1% of a lavender essential oil blend. That is 5 grams of the oil in the batch. If linalool makes up even 3% of that essential oil, which is low for lavender, you are looking at 0.15 grams of linalool in a 500 gram batch. That is 0.03% of the total formula, thirty times over the leave-on trigger.

This is the trap. Makers assume a "trace" amount of essential oil in a light-fragrance product will fly under the radar. It almost never does, because most essential oils are themselves concentrated cocktails of these allergens. A pinch of rose absolute, ylang ylang, or citrus peel oil can push several allergens over 0.001% even at a 0.5% total fragrance load.

Do the math before you guess

The only reliable way to know if you are over or under the trigger is to work backward from your essential oil or fragrance oil's own allergen content, which your supplier should be able to give you, usually as a percentage breakdown or at minimum a list of "contains" allergens above a reporting threshold.

The calculation is simple multiplication, but it has to happen for every allergen your fragrance material contains, not just the obvious ones:

Step	What you do
1	Get the allergen percentage inside the essential oil or fragrance blend from your supplier's documentation
2	Multiply that percentage by the use level of the oil or blend in your finished formula
3	Compare the result to 0.001% for anything leave-on, 0.01% for anything rinse-off
4	Repeat for every named allergen the material contains, since one oil can trigger several at once

Skip the exercise and you either under-disclose, which is the compliance risk, or you assume everything triggers and over-label unnecessarily, which just makes your ingredient panel longer and harder to read.

Two dates, two lists

There is a timing wrinkle worth knowing. The original fragrance allergen set, referred to as List 1, becomes mandatory on the CNF and the label starting April 12, 2026. A second, expanded set aligned with international allergen lists, List 2, follows on August 1, 2026. If you are notifying a leave-on product between those two dates, you are working against List 1 obligations first, then need to revisit the same formula math again a few months later when List 2 kicks in. Common names on these lists include Limonene, Linalool, Citronellol, Geraniol, Eugenol, and Coumarin, all of which occur naturally across a wide range of essential oils, not just synthetic fragrance compounds.

What this means for reformulation

If your lotion, cream, serum, or balm relies on a fragrance blend you have not broken down allergen by allergen, now is the time, well before either 2026 deadline. It is far cheaper to find out during formulation that your rose geranium blend triggers five allergens than to find out after your CNF has already been filed with an incomplete list.

Cosmetic Comply's ingredient matching carries these percentages through automatically, expanding your fragrance blend into its named components and flagging anything that crosses the leave-on or rinse-off threshold before you submit, so the allergen math is not something you are doing by hand on a spreadsheet at the last minute.