Reading the Active Percent Out of a Premade Base

You bought a five-gallon bucket of unscented lotion base, added your own essential oil blend and a botanical extract, and now you need to file a notification. The problem is your supplier's spec sheet lists ten ingredients with no percentages, just an INCI list in descending order. You cannot file "some amount" of anything.

Why this matters more than it seems

A notification needs real concentrations, not vibes. If your base already contains a preservative, and you assume it is preservative-free and add your own on top, you may end up over a restricted limit without realizing it. Same goes for actives. Some bases marketed as "moisturizing" already contain niacinamide or panthenol at a functional level, and if you also add your own, the combined concentration is what actually ends up on skin, not either ingredient counted separately.

Start with the supplier's technical data sheet, not the marketing page

Most base suppliers have two documents: a product page with soft claims, and a technical data sheet (TDS) or spec sheet with harder numbers. The TDS is where you look for:

• A full INCI list in descending order of concentration
• Any percentage ranges given for key components (preservative systems are the most common one disclosed)
• A certificate of analysis, if available, which sometimes includes batch-specific percentages

If the TDS only gives you the INCI list with no numbers, email the supplier directly and ask for percentage ranges on the preservative system and any actives. Most legitimate suppliers will provide this on request, sometimes under a short NDA. If they will not, that is worth treating as a caution flag about the supplier generally.

Working the math backward from INCI order

INCI order tells you rank, not exact numbers, but it still helps. Water is almost always first and typically makes up the bulk of a lotion base, often somewhere in the 60 to 80 percent range depending on the formula. Emulsifiers and emollients typically follow in descending amounts. Preservatives, being used at low levels, usually appear near the end of the list, often below one percent.

If the supplier will not give you a number, you can sometimes estimate a preservative's concentration by checking the INCI names against the preservative's own supplier literature. Most preservative systems are sold with recommended use ranges (for example, a common phenoxyethanol blend might be recommended at a specific percentage range by its own manufacturer). If your base's spec sheet names the preservative system by trade name, you can look up that system's own recommended use level as a reasonable proxy, and note in your records that it is an estimate.

A worked example

Say your bucket of base lists "Phenoxyethanol, Ethylhexylglycerin" near the end of its INCI list, and the supplier confirms on request that this preservative blend is used at 1% of the base. You then add:

Component	Where it comes from	Percent of finished product
Base (as supplied)	97% of your final formula	97%
Preservative blend inside base	1% of the base	0.97% of finished product
Your added essential oil blend	You add at 1.5%	1.5%
Your added extract	You add at 1.5%	1.5%

The preservative blend's real share of your finished product is 1% multiplied by 97%, which comes to 0.97%, not 1%. This is the same multiply-through logic used for any supplier blend: take the blend's concentration in the base, multiply by how much of the base you used, and that gives you its true share of the finished product.

What to do if you truly cannot get a number

If a supplier genuinely will not disclose even a range, and you cannot find the preservative system's typical use level from other public technical literature, treat that as a real limitation rather than something to guess past. Filing a notification with fabricated percentages is worse than pausing to sort out real numbers first. Consider switching to a base supplier who documents their formula properly. Reputable base manufacturers selling into the handmade cosmetics trade generally expect this question and have an answer ready.

Keep this documentation with your batch records

Whatever numbers you land on, keep the supplier correspondence, the TDS, and your calculation on file. If a regulator or a distributor ever asks how you arrived at your listed concentrations, "the supplier's technical sheet plus this calculation" is a real answer. "I guessed" is not.

Cosmetic Comply's ingredient matching walks through exactly this kind of blend expansion, so when you enter a premade base and your added ingredients, it carries the arithmetic through and flags where a supplier's numbers are missing rather than letting a gap slide into the filing unnoticed.