Limonene Levels, Oxidation, and When It Must Be Declared

Limonene is the reason orange peel smells like orange peel. It's the dominant compound in cold-pressed citrus oils, it's cheap, it's pleasant, and it shows up in an enormous share of "fresh" and "citrus" scented cosmetics without anyone deliberately adding it as a standalone ingredient. That last part is exactly why so many makers get caught off guard by allergen disclosure rules. Nobody wrote "limonene" on their ingredient sourcing sheet, they wrote "sweet orange essential oil," and the limonene came along for free.

Where limonene actually comes from in your formula

Limonene is a naturally occurring constituent of many essential oils, most notably citrus oils like orange, lemon, grapefruit, and bergamot, but it also turns up in smaller amounts in other botanicals. If your product contains any of these oils, or a fragrance blend built from them, you likely have limonene in the finished product whether or not it appears anywhere on your ingredient sourcing paperwork by that name.

This matters because Canada's fragrance allergen framework treats limonene as one of the named allergens that must be disclosed once it crosses a concentration threshold in the finished product:

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

Those thresholds sound tiny, and they are, but a fragrance oil is itself often only a small percentage of the total formula, so the actual math usually looks like this: take the limonene percentage within the essential oil or fragrance blend, multiply by the blend's use level in your finished product, and compare that number to the threshold.

A worked example

Suppose your body lotion uses 1% of a fragrance blend, and that blend's technical data sheet or SDS shows it contains 8% limonene.

Step	Calculation	Result
Limonene share of blend	8%	0.08
Blend use level in product	1%	0.01
Limonene in finished product	0.08 x 0.01	0.0008 (0.08%)

0.08% is well above the 0.001% leave-on threshold, so this would need to be declared. This is the calculation makers most often skip, because it's tempting to look at the 1% fragrance load and assume it's too small to matter. It isn't. Always do the multiplication rather than eyeballing it.

Why oxidation is part of this conversation

Limonene oxidizes on exposure to air and light, forming oxidation products that are more likely to cause skin sensitization than fresh limonene itself. This has a couple of practical implications for makers working with citrus oils:

• Storage matters. Citrus oils kept in warm conditions or partially-filled, frequently-opened containers oxidize faster, which can change both the scent and the allergen profile of your fragrance component over time.
• A fresh SDS reading isn't a permanent one. The limonene figure on a supplier's data sheet reflects that lot at that time. It's a reasonable basis for your calculation, but it's not a guarantee that the oil's chemistry stays static in your own stockroom for a year.
• Antioxidant strategies exist, but they're a formulation decision, not a labeling shortcut, they don't remove the need to declare limonene if your calculated concentration is above threshold.

What actually needs to happen on your paperwork

1. Identify every essential oil, absolute, or fragrance blend in your formula.
2. Get the limonene percentage for each from a current supplier SDS or allergen declaration, not an old or generic one.
3. Multiply by use level to get the finished-product concentration.
4. Compare to the 0.001% leave-on or 0.01% rinse-off threshold.
5. If you're over, plan to include limonene on your Cosmetic Notification Form and your label ahead of the April 12, 2026 mandatory date for List 1 allergens.

If your fragrance supplier can't give you a limonene percentage at all, that's worth pushing back on directly, since you can't do the threshold math without it. Cosmetic Comply's ingredient matching step is built to catch this exact pattern, flagging fragrance and essential oil components that commonly carry undeclared allergens so you're not doing this arithmetic from scratch on every single SKU. Small oils, small percentages, but the compliance obligation is real, and it's one of the easier things to get right once you know where to look.