In short
To check a formula against a restriction, work out the share of each restricted substance in the finished product, including what natural materials contribute, and compare it with the limit for that product's category. The guide walks through the method. Below are practice problems using deliberately invented limits, so that no one mistakes them for real ones. For a real check, use the current Standard and your supplier's documents.
What you will learn
- Calculate a material's share in the finished product
- Include constituents contributed by natural materials
- Find the line that sets a formula's maximum dose
Before this lesson: IFRA Categories and QRA: Study Guide
Practice problems, with invented limits
| Problem | Working | Answer |
|---|---|---|
| Material X is 4% of the concentrate. The perfume is 15% concentrate. Invented limit 0.5%. | 0.04 × 0.15 = 0.006 | 0.6%: over the limit |
| Same formula, at what maximum concentrate would X be at the limit? | 0.5 ÷ 4 = 0.125 | 12.5% concentrate |
| Oil Y is 5% of the concentrate and holds an invented 40% of substance Z. A pure line of Z is 1%. Perfume at 10%. | (0.05 × 0.40 + 0.01) × 0.10 = 0.003 | 0.3% Z |
| A material sold at 10% in solvent is 2% of the concentrate. Perfume at 20%. | 0.02 × 0.10 × 0.20 = 0.0004 | 0.04% active |
Practical exercise: Restriction check on your own formula
- Choose one complete formula of your own, and state the product and its category.
- List every line with its true active content, using supplier documents for diluted materials.
- Look up each material and known constituent, recording amendment and date. Where composition data is missing, mark the line "unknown".
- Calculate the finished-product share of each restricted substance, adding contributions.
- Name the limiting line, and work out the highest concentrate it allows.
- Have someone rework two lines by hand, or check two lines using separate software.
You have done this well if the sum for each substance includes contributions from naturals, unknowns are marked rather than ignored, and a second check agrees. This is a self-check and does not replace a supplier's certificate or a safety assessment.
Knowledge check
Written and reviewed by the RUŌOD Lab team. This is general education, not legal, regulatory, medical or safety advice. Example dilutions and exercises are for learning, are not validated products, and have not been safety-assessed. Completing a lesson confers no qualification. How we check these lessons.