How to calculate IFRA limits in a perfume formula

An IFRA limit is a ceiling on how much of one substance may be in the finished product a person wears. That sentence carries the three things people get wrong: it is per substance and not per bottle, it is measured in the finished product and not in the concentrate, and a natural oil is not one substance. Get those three right and the rest is multiplication.

Step one: work in the finished product, not the concentrate

A formula is usually written as a concentrate, and the concentrate is then diluted in alcohol to a strength. The limit applies after that dilution. So a material's share in the finished product is its share of the concentrate multiplied by the concentrate's share of the finished product. A line that is a tenth of the concentrate in a product that is a fifth concentrate is a fiftieth of what goes on skin. Compare that number, not the line's percentage, with the limit.

Step two: count the dilution you weighed from

If a line was weighed from a stock solution, only the aromatic part of it counts. A gram of a ten percent dilution puts a tenth of a gram of the material into the beaker and nine tenths of a solvent that never appears in the formula. Every share above has to use the corrected figure, or the check is off by the dilution factor. The formula calculator does this correction for every line.

Step three: open the naturals

Most limits are written on molecules, and a natural is a few dozen of them. Lemongrass oil carries citral; clove carries eugenol; a rose oil carries citronellol and geraniol. The limit is on the molecule, so the share of the natural in the product is multiplied by the molecule's share of the natural. That needs a composition for the natural, which is why a formulation tool that cannot see inside an oil cannot really check it. PerfuMate ships an estimated constituent table for the naturals it carries, and takes your own supplier analysis over its estimate whenever you paste one.

Step four: sum the same molecule across every source

This is the step a hand calculation misses. If citral arrives from lemongrass, from a lemon oil and from a bottle of citral itself, the product contains one total of citral, and that total is what the limit is on. Three lines each under the limit can add up to a product over it. The check has to be per molecule, across the whole formula, after the two corrections above.

Step five: pick the category, and stamp the amendment

Limits differ by what the product is, because a fine fragrance, a hand cream and a candle meet skin differently. Category 4 is fine fragrance applied to skin, and that is the category most independent perfumers mean. Limits also move between amendments, so a check is only as current as the amendment it was computed against, and it should say which one. Verify against the official standards before anything is sold; a tool's check is an instrument, not a certificate.

What the bench does with all this

PerfuMate runs the five steps while you compose: every line is corrected for its dilution, every natural is opened into its constituents, every molecule is totalled across the formula, and the total is compared with the Category 4 limit for the amendment named on the sheet, live, so a line that pushes a total over the ceiling says so before you weigh it. The full account of the data and how far to trust it is at the IFRA answer, and the background reading is IFRA for independent perfumers. The quickest way to understand a limit is to meet one while building: Open the bench.