The Leave-On Versus Rinse-Off Allergen Threshold Gap

Two products, same essential oil, same percentage in the formula. One needs the allergen disclosed, the other doesn't. That's not a mistake, it's the leave-on versus rinse-off gap, and it trips up more formulators than almost any other threshold in cosmetic compliance because it's easy to assume one number applies everywhere.

The two numbers

Fragrance allergen disclosure in Canada is triggered at two different concentrations depending on how the product is used:

• Leave-on products: above 0.001% (10 ppm)
• Rinse-off products: above 0.01% (100 ppm)

That's a tenfold difference. A body lotion you leave on your skin all day has a much lower disclosure threshold than a shampoo you rinse out in under a minute. Same allergen, same regulatory framework, ten times the tolerance for the product you wash away quickly.

Why the gap exists

The logic follows exposure time. A leave-on lotion, cream, or serum keeps the allergen in contact with skin for hours, which means more opportunity for someone with a sensitivity to react. A rinse-off product, shampoo, body wash, cleansing bar, has brief skin contact before it goes down the drain. Less contact time generally means less concern at a given concentration, which is why the rinse-off threshold is set higher.

This means you cannot use a single allergen number across your whole product line and call it done. A brand that makes both a leave-on body butter and a rinse-off body wash needs to run the allergen math separately for each, even if they share the same fragrance oil.

Working through both numbers with a real example

Say you're using a fragrance oil that's 2% Linalool by weight of the fragrance blend, and you're dosing that fragrance oil at 1% in your finished product.

Linalool concentration in the finished product = 2% x 1% = 0.02%, or 200 ppm.

• In a leave-on product, the threshold is 10 ppm. Your 200 ppm is way above that, disclosure required.
• In a rinse-off product, the threshold is 100 ppm. Your 200 ppm is still above that, so disclosure is required here too.

Now say you dose the same fragrance oil at a lighter 0.3% in a rinse-off shampoo.

Linalool concentration = 2% x 0.3% = 0.006%, or 60 ppm.

• In a rinse-off product, 60 ppm is under the 100 ppm threshold, no disclosure needed for this particular allergen.
• If that same 0.3% dosing were used in a leave-on product instead, 60 ppm is still well above the 10 ppm leave-on threshold, disclosure would be required.

Same fragrance oil, same dosing percentage, different outcome purely because of product category.

A reference table

Scenario	Threshold that applies	Practical takeaway
Body lotion, serum, leave-on conditioner	10 ppm (0.001%) leave-on	Even trace fragrance allergen levels often clear this threshold
Shampoo, body wash, rinse-off mask	100 ppm (0.01%) rinse-off	More headroom before disclosure kicks in
A product line with both formats	Both thresholds, calculated separately	Never assume one calculation covers both products

Timeline to keep in mind

The original fragrance allergen set, List 1, becomes mandatory on the CNF and on the label as of April 12, 2026. An expanded set, List 2, aligned with international lists, becomes mandatory August 1, 2026. Both thresholds described above apply once these disclosure requirements are in force, so if you're formulating or reformulating now, it's worth running this math today rather than waiting until the deadline is close.

Practical steps for your own formulas

1. Classify every SKU clearly as leave-on or rinse-off before you calculate anything, don't guess based on the product category name alone
2. Get the full allergen breakdown of every fragrance and essential oil you use from your supplier, not just a marketing description
3. Multiply each allergen's percentage in the fragrance by your fragrance's use level in the finished formula, twice if you're using a supplier blend within a blend
4. Compare the result against the correct threshold for that specific product's use pattern

If you're running this calculation across a full line of leave-on and rinse-off products and want a second check on the arithmetic, Cosmetic Comply screens ingredient lists against the current allergen thresholds automatically, applying the right leave-on or rinse-off number to each product before a compliance reviewer signs off, so the math doesn't rest entirely on a spreadsheet you built at midnight.