Bisabolol is a small sesquiterpene alcohol with a reputation for being gentle, and it appears in an enormous number of soothing and after-sun formulations. It is also one of the easier cosmetic actives to mis-specify, because “bisabolol” covers both a natural enantiomer and a synthetic racemate that behave the same in most formulas but are priced very differently. This guide is about buying the right one, using bisabolol as the case.
The molecule and its two identities
The published identity is CAS 515-69-5, molecular formula C15H26O, molecular weight 222.37 Da, PubChem CID 1549992, and IUPAC name (2R)-6-methyl-2-[(1R)-4-methylcyclohex-3-en-1-yl]hept-5-en-2-ol. It is a tertiary alcohol with one double bond in the ring and one in the side chain, and it carries two stereocentres.
Those stereocentres are the whole commercial story. The natural material, obtained from the essential oil of Matricaria recutita and related sources, is the (-)-alpha enantiomer and is optically active. Synthetic material is typically produced as a racemate and is optically inactive. Both are legitimately sold as bisabolol; only one supports a natural-origin claim.
The numbers that belong on a specification
| Parameter | Typical value | Discriminating power |
|---|---|---|
| CAS number | 515-69-5 | Confirms alpha-bisabolol, not a positional isomer |
| Molecular formula | C15H26O | Tertiary alcohol, two C=C bonds |
| Molecular weight | 222.37 Da | GC-MS identity check |
| Assay by GC | 95% and above for cosmetic grades | Lower indicates diluent or isomers |
| Optical rotation | Strongly negative for natural; near zero for racemate | The single best origin discriminator |
| Relative density | Roughly 0.92 g/cm3 at 20 °C | Cheap screening check |
| Refractive index at 20 °C | Roughly 1.493–1.497 | Sensitive to dilution |
Ask for optical rotation explicitly. A supplier who quotes only a GC purity figure has left the origin question open, and that is exactly where the price difference lives.
Natural versus synthetic: an honest comparison
| Dimension | Natural (-)-alpha-bisabolol | Synthetic racemate |
|---|---|---|
| Origin | Chamomile-type essential oil fraction | Chemical synthesis |
| Optical rotation | Strongly negative | Approximately zero |
| Assay | Often 95% plus, with isomer profile | Often 95% plus |
| Supply stability | Tied to botanical harvest | Independent of harvest |
| Certification support | Can support natural-origin claims | Cannot |
| Price position | Higher and more volatile | Lower and steadier |
There is no universal “better” here. If your brand is making a natural-origin or certified claim, you need the natural material and the documentation to prove it. If the formulation simply needs the functional properties and the label does not make an origin claim, the synthetic material is a rational and often more secure supply choice.
Where the lot actually fails
Bisabolol is a sesquiterpene alcohol with two double bonds, so oxidation is the main risk. Oxidised material develops a stale, terpenic odour and can become a sensitiser, which is precisely what a soothing active must never do. Three controls matter:
- Oxygen exclusion. Nitrogen headspace in drums, minimal ullage, and tightly sealed closures.
- Temperature. Store cool. Long holds above ambient temperature accelerate oxidation measurably.
- Trace metals. Iron and copper catalyse terpene oxidation. Confirm the material was not handled in reactive metal, and check the heavy-metal screen.
Peroxide value is not the standard control for a terpene alcohol; odour assessment and a GC profile that shows the oxidation products are more informative. Ask for both on a retained sample.
Formulation handling, briefly
The material is oil-soluble and is normally added to the oil phase or post-emulsification at low temperature. Reported use levels in cosmetic literature are typically well below one percent, and higher levels rarely improve performance while increasing cost and odour load. Because it is a tertiary alcohol it is relatively resistant to esterification and to hydrolysis, which makes it a tolerant ingredient in most systems.
Documentation checklist
- GC assay with the method and column named, plus the isomer profile.
- Optical rotation, with the temperature and wavelength stated.
- Identity confirmation by GC-MS or IR.
- Origin declaration, including botanical source and country, for natural grades.
- Heavy metals, and residual solvents for synthetic grades.
- IFRA or fragrance-allergen information if the material will be declared as a fragrance component.
- Organic transaction certificate if a certified claim is intended.
Frequently asked questions
How do I know which one I received?
Optical rotation. A strongly negative value indicates the natural enantiomer; a value near zero indicates a racemate. GC purity alone will not tell you.
Is the synthetic material less effective?
In most formulations, no meaningful difference is reported. The difference is in origin, certification support and price, not in baseline functionality.
Why does the odour vary between lots?
Oxidation, or a different isomer profile from a different botanical source. Compare the GC trace against your retained reference sample.
What shelf life is realistic?
Two years or more, sealed, cool and under inert headspace. Once opened, consume quickly and re-blanket if possible.
Can I declare it as a natural ingredient if I use the racemate?
No. That would be a false claim. Match the material to the claim before you finalise the label copy.
The short version
Bisabolol is CAS 515-69-5, C15H26O, 222.37 Da, and it comes in two commercially distinct forms separated by optical rotation rather than by purity. Specify the origin you need, insist on optical rotation alongside the GC assay, and control oxygen, temperature and trace metals through storage. Do those three things and the material is one of the more predictable actives in a soothing formulation.