Hair Dye Ingredients You Must Declare and Restrict

Hair colour is one of those categories where makers who've filed a dozen other cosmetics without incident suddenly hit a wall. It's not that the notification process itself is different, it's that the ingredient chemistry involved is genuinely more tightly controlled than a moisturizer or a bar of soap, and the restrictions are unforgiving about precision.

Why oxidative dyes get special attention

Permanent and semi-permanent hair dyes rely on small aromatic amine molecules, most famously p-phenylenediamine, often abbreviated PPD, which react with an oxidizing agent (usually hydrogen peroxide) inside the hair shaft to form the actual colour molecule. These precursor molecules are effective at what they do partly because they're chemically reactive, and that same reactivity is what makes them a known sensitizer for a meaningful portion of the population. Once someone becomes sensitized to PPD, reactions can range from mild irritation to serious allergic responses.

Because of that sensitization risk, oxidative dye ingredients like PPD sit on restricted ingredient lists with defined concentration limits, rather than being banned outright, since they remain in wide legitimate use. Getting the concentration right, and confirming your specific formula falls within the current limit, is the central compliance task for anyone formulating or private-labeling a permanent hair colour product.

What you actually need to check

The concentration limits for oxidative dye ingredients are set by each market's regulator and they do get revisited over time, so treat any specific percentage you've seen elsewhere as something to verify against the current source rather than something to assume is still accurate. What stays constant is the process:

1. Identify every dye precursor and coupler in your formula by INCI name, not just the trade name your supplier gave the premixed dye base.
2. Confirm the CAS number for each, since some dye ingredients are sold under names that map to more than one registered substance depending on the salt form.
3. Calculate the actual concentration in the finished, ready-to-use product, which for a two-part hair dye means accounting for the dilution that happens when the colour base is mixed with the developer.
4. Check that concentration against the current restricted ingredient limit for the market you're filing in.

That fourth step, calculating the "as mixed" concentration rather than the concentration in the undiluted colour tube, is where a lot of errors creep in. A dye base sold at a certain PPD percentage, once mixed 1:1 with a developer, ends up at roughly half that concentration in what actually touches the scalp. Filing the undiluted number instead of the diluted, applied number can make a compliant product look non-compliant on paper, or worse, mask a real problem.

Ingredients that commonly show up in hair colour filings

INCI name	Typical role	Regulatory note
p-Phenylenediamine	Primary oxidative dye precursor	Restricted, concentration limit applies, known sensitizer
Toluene-2,5-Diamine	Alternative dye precursor	Restricted, similar sensitization profile to PPD
Resorcinol	Dye coupler	Restricted, concentration limit applies
Hydrogen Peroxide	Oxidizing developer	Concentration-dependent, separate handling considerations
Ammonia	Alkalizing agent for cuticle lift	Generally permitted, check current concentration guidance

Botanical or semi-permanent colour options, like henna-based products, carry a different risk profile since they don't rely on the same oxidative chemistry, but they're not automatically exempt from scrutiny either. Compound henna products sometimes have undisclosed PPD or metallic salts added to intensify or alter colour, and that's exactly the kind of undisclosed ingredient that becomes a serious labeling and safety problem, not just a paperwork one.

The patch test expectation

Because of the sensitization risk associated with oxidative dyes, many markets and industry norms around permanent hair colour products expect a patch test recommendation on the label, telling the consumer to test a small area before full application. This isn't a regulatory filing detail exactly, but it's closely tied to the same underlying risk that puts PPD on a restricted list in the first place, and it's worth building into your label copy and customer instructions regardless of what a specific filing form asks for.

Filing the notification with the right detail

For a Canadian filing, this all comes back to listing every ingredient in the formula, including the developer if it's sold and used as part of a defined system, by INCI name with an accurate concentration, and checking each one against the Cosmetic Ingredient Hotlist. Hair dye formulas tend to have more ingredients that land in restricted rather than unrestricted territory than a typical lotion or cleanser, so it's worth budgeting extra care, and extra time, for getting the concentration math right before you submit.

Cosmetic Comply handles exactly this kind of concentration-sensitive filing, mapping each dye ingredient to its INCI name and CAS number, calculating real finished-product concentrations including supplier blend expansion, and flagging anything that needs a closer look against the current restricted list before a human reviewer signs off and the notification goes in.