Material guide: linalool — the ubiquitous molecule that makes oxidation visible

Linalool enters formulas through lavender, bergamot, coriander and many floral materials. It opens this guide because an ageing bottle makes one practical lesson easy to smell: exposure to air changes the material in the bottle.

What matters

• Linalool is everywhere: lavender, soap, shampoo. The first molecule a beginner should know.
• It is gentle in itself, but it oxidises with age, and only then does it irritate skin. Keep the bottle sealed and dark, and write down the opening date.
• When buying, check two things: the name (laevo or standard grade) and the manufacture date. Fresher is better.

The record

CAS	78-70-6
Formula	C₁₀H₁₈O (monoterpene alcohol)
MW	154.25
Odour	citrus, floral, sweet, bois de rose, woody, green, berry, waxy
Strength	medium
Substantivity	12 h (neat, on a strip)
Specific gravity	0.858–0.867 (25 °C)
Boiling point	194–197 °C
Shelf life	24 months or longer (cool, dark, sealed)

If the table looks foreign, the plain version: CAS is the molecule's worldwide ID number. Specific gravity says whether it is heavier or lighter than the same volume of water (below 1 = lighter), and substantivity is how long you can still smell it on a test strip.

(Our database record. Gravity and shelf life are a specification band and a floor rather than single values; see weighing and storage.)

What it is

The 2008 review by Kamatou and Viljoen in Natural Product Communications places the molecule properly: linalool is a monoterpene alcohol occurring naturally in many aromatic plants, and one of the most sought-after compounds in the flavour and fragrance industry.

Its role goes well beyond being "a floral note":

Linalool is also a key compound for the industrial production of a variety of fragrance chemicals such as geraniol, nerol, citral and its derivatives, as well as a lead compound in the synthesis of vitamins A and E.

The same review covers its role in pollination biology, its insect-repellent properties, and its antimicrobial and anti-inflammatory activities. Small wonder nearly every soap, detergent and shampoo contains it.

Our natural_synthetic field marks it "both": it is in lavender, ho wood and rosewood, and the overwhelming majority of world supply is synthetic. Same molecule either way. That is the argument of the batch variation article, and linalool is its best example.

Smelling it

Our record carries 11 descriptors: citrus, floral, sweet, bois de rose, woody, green, blueberry, orange, terpenic, waxy, rose. The list is that wide because the material genuinely is that many-sided, which is also why it fits into almost any formula.

Practical points:

• Evaluate at 10%. Medium strength; no need to go weaker, but neat will mislead you (dilution).
• It sits mid-curve: 12 hours of substantivity, longer than citrus, shorter than woods. When your top and base will not join, this is often the patch — the reason it made the ten in the first accord.
• Mind the isomers. The same molecule comes in "left-hand" and "right-hand" mirror versions: natural lavender is mostly the left-handed one (laevo-linalool in catalogues), while synthetic material is usually a half-and-half mix (the racemate). Different catalogue items, different smells. My own first order went wrong here; I skimmed the name and ended up with the racemate. Our database holds 44 supplied variants whose names contain linal*, so read the name carefully.

Its first lesson: oxidation

Linalool is the protagonist of the storage article; only the conclusion here.

In 2004 Sköld and colleagues showed that pure linalool does not trigger skin allergy in the standard assay, while air-exposed samples do. The culprits are the hydroperoxides formed as it oxidises (plainly: oxygen turns part of the linalool into a different, skin-irritating substance), one of which reached 15% of an oxidised sample.

Hence our record's storage advice (cool, dark, sealed), and its close relative laevo-linalool sitting on the strictest list: store under nitrogen. In practice, decant, date the opening, keep a retain. A three-year-old open bottle of linalool is not a depreciated asset. It is a different substance.

Regulatory

Our record lists it on: GRAS, JECFA, CoE, FEMA GRAS, IFRA.

The usual reminder: this means "appears on these registers" and contains no limit values. Current IFRA attention on linalool is tied directly to oxidation: the industry's concern is controlling hydroperoxides (peroxide value), not banning the molecule. For anything going on skin, consult the current IFRA Standards and the supplier's specification, and watch the batch's peroxide value.

Buying it

One of the easiest materials in the starter palette to obtain: 135 supplier records in our database, and virtually every small-quantity retailer stocks it. Three things to check:

1. Isomer: laevo or racemic; the catalogue name will say.
2. Batch number and manufacture date. As above, what you are really buying is time-until-oxidised.
3. Peroxide value on the specification. This number means "how much has already oxidised", and since the irritant is the oxidation product, it matters more than purity.

→ Linalool in the database: full properties, supplier list, suggested pairings. → Search by odour: try combinations like "floral woody" to find its neighbours and substitutes.

References

G. P. P. Kamatou & A. M. Viljoen, Linalool – a review of a biologically active compound of commercial importance, Natural Product Communications, 3(7), 1183–1192 (2008). doi:10.1177/1934578X0800300727

M. Sköld, A. Börje, E. Harambasic & A.-T. Karlberg, Contact allergens formed on air exposure of linalool, Chemical Research in Toxicology, 17(12), 1697–1705 (2004). PMID 15606147