Castor oil labels love the word "pure". A lab report is how you check it. Here's what ricinoleic acid is, why the percentage matters, and what else to look for on a certificate of analysis.
What is ricinoleic acid?
Ricinoleic acid is the fatty acid that makes castor oil unlike any other plant oil. It has an extra hydroxyl group in its structure. That's why castor oil is so thick, and why it clings to hair and lashes instead of sliding off.
What's a normal percentage?
Castor oil is mostly ricinoleic acid. Studies of different castor varieties report roughly 83% to 89%, depending on the plant and growing conditions. The rest is mainly oleic and linoleic acid. An oil testing at 90% sits at the high end of what castor seeds produce.
For comparison, BIOCENTIC's castor oil tests at 90% ricinoleic acid, 3% oleic acid and 4% linoleic acid.
A much lower number is a warning sign. It can mean the castor oil was blended with cheaper oils, or pressed from lower-quality seed.
How to read a castor oil lab report
A certificate of analysis (COA) from an independent lab lists the tests run on a specific batch. These are the lines worth reading:
- Batch or lot number. It should match the number on your bottle. A report without one could belong to any oil.
- Fatty acid profile. Ricinoleic acid should be the large majority, with small amounts of oleic, linoleic and others.
- Free fatty acids or acid value. Lower means fresher oil that has broken down less.
- Heavy metals. Look for results below the limit, often written as "not detected" or a figure in parts per million.
- Lab name. A lab that is not the seller.
How BIOCENTIC tests
Every BIOCENTIC batch is tested by a lab before it's bottled, and every number we print comes from those tests. Our 500 mL castor oil and 50 mL lash and brow oil come from the same tested oil.
Sources
Wang et al., 2009: ricinoleic acid 83.41–88.94% across castor accessions Shah et al., 2013, Journal of Oilseeds Research: 84.3–87.8% across 18 genotypes
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