Fixative or Solvent – What Fragrance Fixation Really Is
Two patents, one word, opposite meanings
In the winter of 1978 a German company patented a fixative for perfumery. Eleven months later an American company patented its own – and called it almost the same thing.
The two substances had nothing in common. One is an odorous molecule that a proportion of people simply cannot perceive. The other is a sugar derivative with no smell at all. The mechanisms are opposites: one works through perception, the other through evaporation.
And both documents were right. The word they used denotes not one phenomenon but several.
It has stayed that way ever since. “Fixative” is the most overloaded term in perfumery: at least four different physical events fit underneath it, and they are not interchangeable. This page sorts out which is which, and what each of them can actually do.
The short answer
Fixative is a functional term, not a mechanistic one. It describes the result – the fragrance lasts longer – but says nothing about how. Hence the confusion.
| Mechanism | What it does | Examples | Dosage |
|---|---|---|---|
| Thermodynamic | Lowers the vapour pressure of the volatile components | Methyl glucoside polyols (Glucam) | 1–2.5% |
| Perceptual | Outlasts the top note itself and creates an impression of continuity | Labdanum, benzoin, musks, ambroxan | 3–25% |
| Adhesive | Clings to skin or fibre and mechanically retards evaporation | Film formers, polymers | system-dependent |
| Low-volatility solvents | Fix nothing. They change the concentration | DPG, IPM, benzyl benzoate, diethyl phthalate | 20–90% |
The first three mechanisms genuinely extend the drydown, each in its own way. The fourth extends nothing at all, although reference works place it in the same row. This is no small matter: it is precisely what lies behind most disappointments when a “fixative” has been bought, added – and nothing happened.
1978: The fixative you cannot smell
In February 1978 the German company Dragoco Gerberding of Holzminden files a patent titled “Fixative for perfume compositions”. The substance: 1-(2,6,6-trimethylcyclohexyl)-hexan-3-ol. Today it is known as Timberol and sold as a woody-ambery odorant.
But it was not patented as a smell. It was patented as a fixative – and the reasoning deserves to be read in full:
“Anosmia, i.e. the incapability to perceive smells, which numerous people have with respect to this new alcohol, may be compared with the effect of various very expensive animalic fixatives, such as musk and amber, whose scent can also be noticed only faintly by certain people, or not at all. The occurrence of anosmia with respect to a specific substance, particularly in the area of perfumery, appears to always point out to particularly good fixative properties of a substance.”
Dragoco's chemists put forward a hypothesis: anosmia and fixative power are connected. And – what lifts the application above mere marketing – they offered a control case. The close relatives of their molecule, iso- and n-tetrahydromethylionol, show no fixative effect whatsoever. And no cases of anosmia to them have been recorded either.
The hypothesis is shaky and cannot be considered proven. But it does explain a striking regularity: the classical list of fixatives contains precisely those substances to which anosmia is widespread. Ambroxan – around 20% of people do not perceive it, or perceive it only weakly. Musks. Amber itself.
The dosages in the patent are enormous by today's standards: 1 to 25%, with a distinct effect from about 3%. In the soap composition of the example it is 22.8%. The result is phrased like this: the addition “imparts to the previously somewhat dull and flat-smelling perfume composition a long-lasting, radiant and natural fragrance”.
This is fixation of the first type in its purest form: it is not physics that works, but perception.
1979: The fixative as physics
Eleven months pass. In December 1979 the American Amerchol Corporation files a patent – and also calls it “Polyol fragrance fixatives”. The substance belongs to an entirely different class: methyl glucoside polyols. A sugar backbone with polyether chains grafted onto it. They are sold under the name Glucam.
The approach is the exact opposite. Not “a smell not everyone perceives”, but a substance with no odour at all that intervenes in evaporation.
And here the patent does something one does not expect from a legal document. It lists the fixatives of its time – absolutes, resinoids, animal secretions, macrocyclic and nitro musks – and adds:
“In addition to the foregoing materials, some references in the art to other synthetic materials having no odor of their own as fragrance fixatives have been made to ethylphthalate and to benzyl benzoate. Actually, these materials do little to strengthen and prolong the fragrance of fragranced materials, but they are useful as low volatility solvents for a broad range of fragrance materials.”
Forty-five years ago, in plain words. Exactly the line that is still rarely drawn today.
The patent's second point matters no less: classical fixatives “can distort the nature or character of the fragrance being fixed”. They smell themselves – and so, in prolonging a composition, they alter it. An odourless substance does not create that problem.
And the third, rarely considered today: solubility. “The methyl glucoside polyols of this invention are soluble in water, alcohol and water-alcohol systems. Most fixatives of the prior art are insoluble in water.”
What the trials showed
Panel tests are attached to the application. This is not advertising but data submitted to the patent office.
| Composition | Dose | On skin | On blotter |
|---|---|---|---|
| Perfume, aldehydic-floral 12% | 2.5% | 97% | 94% |
| After-bath splash | 2.0% | 93% | 90% |
| Eau de toilette, herbal-woody 8% | 2.0% | 95% | 89% |
| Cologne, citrus-floral 5% | 1.0% | 93% | 86% |
| Soap bars | 2.0% | 94% more intense | – |
The percentages give the share of panelists who found longer lasting power compared with the control without the additive. The skin tests ran over one to ninety-six hours.
A separate trial concerned the pungency of alcohol. Denatured alcohol SD-40 with the additive: at 2%, one hundred percent of panelists called the sample less pungent; at 1% it was 83%, at 0.5% still 67%.
And the commercially most telling result: in a cologne the perfume oil was reduced from 5% to 4% and 2% fixative added. 85.7% of panelists judged the result equal or better. In a perfume the same from 12% to 10% – 71.5%.
In fairness: these are self-reports from people, not instrument measurements. Normal methodology for 1979 – but these figures do not carry the precision of a measurement.
What physics says – and where it falls silent
The textbook explanation runs: a non-volatile substance lowers the mole fraction of the volatile components and with it their partial pressure. That is Raoult's law. The direction of the effect is undisputed.
But that is usually where people stop – and this is exactly where the simplification begins.
Raoult's law describes ideal solutions. A perfume composition is never ideal: alcohols, aldehydes, esters, polyols with hydrogen bonds. Real behaviour is described through activity coefficients, and deviations from ideality occur in both directions. To say “a fixative works by Raoult's law” is to tell half the truth.
Even within physical fixation there is more than one mechanism. Ullmann's Encyclopedia of Industrial Chemistry names not only dilution but also hydrogen bonding between the fixative and the components. The Coty patent discussed below adds a third – adhesion to the substrate, that is, to skin and hair. Even official sources do not reduce fixation to a single effect.
From which follows the conclusion that made the whole sorting worthwhile: fixation is not a single phenomenon. Trying to explain it with one formula is as hopeless as explaining it with one word.
2021: The industry changes the word
In June 2020 Coty files an application titled: “Fragrance composition comprising a fragrance component and a non-odorous fragrance modulator”.
The word “fixative” has vanished from the title.
What is inside reads almost like a detective story.
Glucam is named explicitly. In the modulator table the first two footnotes read “available as GLUCAM™ P-20” and “available as Glucam™ E-20”. The text states outright that the composition is compared with a control “lacking any of the disclosed non-odorous fragrance modulators such as Glucam”.
Dragoco is named too. A footnote points to patent US 4,313,855 – the very one from February 1978. Coty thus places both competing approaches from forty years ago into a single table.
The anosmia hypothesis survived. The definition of “substantially non-odorous” explicitly includes “materials that are perceivable only by a minority of people or those materials deemed anosmic to the majority of people”. The guess made by the chemists of Holzminden has entered the legal definition of a present-day patent.
The mechanism is named twice over. The modulator acts by “lowering the vapor pressure of the fragrance materials and increasing their adherence to the substrate (skin and/or hair)”.
And above all: the solvents are set apart. The patent lists as non-volatile solvents: benzyl benzoate, diethyl phthalate, isopropyl myristate, propylene glycol, dipropylene glycol, triethyl citrate. And records that, for the purpose of calculating the fragrance component share, “the total fragrance components does not include non-volatile solvents”.
In 2021 Coty draws exactly the line Amerchol drew in 1979.
The pyramid is abolished along the way. Instead of the subjective division into top, heart and base, Coty introduces a measurable threshold: low volatility means a vapour pressure below 0.001 Torr at 25 °C. The reasoning is in the patent itself: this method “avoids the problem of different classifications for the same fragrance material according to the traditional approach that relies on their subjective characteristic character”.
The four solvents mistaken for fixatives
Four substances are at issue: isopropyl myristate, dipropylene glycol, diethyl phthalate and triethyl citrate. All four are useful, necessary and indispensable in perfumery. And all four are listed somewhere as fixatives – in reference works, by suppliers, in Ullmann's.
Let us start with the numbers, because they settle the question.
| CAS | Formula | Molecular weight | Boiling point | |
|---|---|---|---|---|
| Dipropylene glycol (DPG) | 25265-71-8 | C₆H₁₄O₃ | 134.17 | 230.5 °C |
| Triethyl citrate (TEC) | 77-93-0 | C₁₂H₂₀O₇ | 276.28 | 294 °C |
| Diethyl phthalate (DEP) | 84-66-2 | C₁₂H₁₄O₄ | 222.24 | 298–299 °C |
| Isopropyl myristate (IPM) | 110-27-0 | C₁₇H₃₄O₂ | 270.45 | 309 °C |
| Glucam P-20 – for comparison | 61849-72-7 | polyether | ≈ 1,350 (calculated) | > 316 °C |
Why low volatility is not enough
All four solvents boil between 230 and 310 degrees. Glucam boils above 316. There is a difference, but it is no chasm – in terms of “heaviness”, IPM and Glucam are almost neighbours.
So it is not about heaviness. A substance's own low volatility is a necessary but not a sufficient condition. What makes a fixative is not how reluctantly it evaporates itself, but whether it affects the escaping tendency of the other components.
A solvent simply stands alongside. A fixative – at least as the patents have it – interacts with the volatile components: through hydrogen bonds, through association, through retention on the skin.
Hence the disappointment, too. In a finished alcoholic perfume the real diluent is ethanol, and it leaves first. What remains on the skin is the oil together with the heavy solvent. The solvent dilutes that residue and thereby lowers the concentration in the air above the skin. The result: the fragrance becomes quieter, not longer. The feeling that things got worse although a “fixative” was formally added comes from exactly this.
An honest qualification: the boundary is not absolute but gradual. Some industry sources attribute a weak fixative effect to diethyl phthalate and triethyl citrate, and it cannot be ruled out. But between “a weak, disputed effect” and “a fixative” lies a difference worth naming.
Dipropylene glycol
The lightest of the four and the cheapest. Miscible with water in any ratio, almost odourless, flash point 121 °C. The standard diluent for laboratory solutions and diffusers.
It is declared a fixative more often than the others – probably because it is the cheapest and the first a beginner meets. By boiling point it is the most volatile in this table: 230 °C against 309 °C for IPM.
Triethyl citrate
A citric acid ester, listed as food additive E1505. Water-soluble at 65 g/l, which is unusual in this company. Often sold as a “natural alternative to phthalates”, and in that role it is displacing DEP.
Its reputation as a fixative is the most persistent of all. The vapour pressure genuinely is low – 0.00189 mmHg. But a low vapour pressure of the substance itself and a lowering of the vapour pressure of its neighbours are two different claims.
Diethyl phthalate
The classic diluent of twentieth-century perfumery, for decades the basis of denatured alcohol. Boiling point 298 °C, log P 2.42, only weakly water-soluble at about 1 g/l.
It is precisely the ethyl phthalate that the Amerchol patent in 1979 described as a material that does “little to strengthen and prolong the fragrance”. Today it is being displaced for reasons that have nothing to do with perfumery: as a phthalate it carries a regulatory and reputational burden, and the industry is moving to TEC and benzyl benzoate.
Isopropyl myristate
The heaviest and highest-boiling of the four – 309 °C. And at the same time the most obviously non-fixative: log Pow 7.71, practically insoluble in water at under 0.05 mg/l.
Its strength lies elsewhere. A viscosity of 5–6 mPa·s gives a fine spray pattern; on the skin it is light and does not cling. It is the best carrier for oil perfumes, roll-ons and sprays – and we list it as a carrier precisely, not as a fixative. Readily biodegradable: 91.4% in 28 days by OECD 301B.
One note that has nothing to do with fixation but matters: IPM is considered comedogenic and acts as a penetration enhancer. For perfume on the wrist that is irrelevant; for facial products it is not.
In practice: what for what
The top note breaks off too early, the composition is otherwise good. A thermodynamic task. Glucam P-20 at 1–2.5% of the alcoholic or aqueous portion. It brings no character of its own and therefore does not touch the composition.
The base is empty, the fragrance feels flat after the first hour. This is not a task for a fixative in the physical sense. What is needed is material with a body of its own: labdanum, benzoin, macrocyclic musks, ambroxan. They do not slow the evaporation of the top note – they give substance to what remains.
The alcohol stings in the nose and burns on the skin. A separate task, unrelated to longevity. Glucam P-20 from 1%; according to the patent, at 2% every panelist noticed the effect.
A concentrate needs diluting or an oil perfume building. That is the work of isopropyl myristate, DPG, TEC or benzyl benzoate. Good, necessary work – simply not fixation. The choice between them is decided by solubility, skin feel and spray pattern, not by longevity.
What a fixative cannot do
It will not make the top note durable. A physical fixative slows the departure of the light components but does not cancel it. A citrus note that lives ten minutes may live half an hour. Not three hours.
It will not rescue a weak composition. If a fragrance falls apart because there is nothing left to sound in the second hour, fixation stretches the emptiness rather than filling it.
It is never free. Physical fixatives in excess flatten the evaporation until the composition loses relief. Perceptual ones in excess simply become audible and rewrite the character.
It does not replace testing. The only reliable way to judge the effect: two identical batches, one with the additive, one without, compared after twenty minutes and after two hours. The difference shows at the transition from top to heart, not in the first minute.
Frequently asked questions
What is a fixative, exactly?
A functional term: it describes the result, not the mechanism. At least four different phenomena are gathered under it – lowering of vapour pressure, perceptual continuity of the base, adhesion to the substrate, and plain dilution. The first three genuinely extend the drydown; the fourth does not.
I added DPG and nothing changed. Why?
Because dipropylene glycol is a low-volatility solvent, not a fixative. It dilutes and carries the composition but barely touches evaporation. The same applies to benzyl benzoate and isopropyl myristate: all are useful, just not for this task.
If a solvent is non-volatile, why does it not hold the fragrance?
Because a substance's own low volatility is a necessary but not a sufficient condition. IPM boils at 309 °C, Glucam P-20 above 316 °C – the difference is small. What makes a fixative is not how reluctantly it evaporates itself, but whether it affects the escaping tendency of the other components.
Is triethyl citrate a fixative or a solvent?
A solvent. It is often sold as a “natural alternative to phthalates” and almost always described as a fixative, but its low vapour pressure concerns the substance itself – which is not the same as lowering the vapour pressure of its neighbours. The Coty patent of 2021 lists triethyl citrate among the non-volatile solvents.
How do diethyl phthalate and triethyl citrate differ?
In practice hardly at all: both boil around 295 °C, both are nearly odourless, both dilute. The difference is regulatory – DEP is a phthalate and carries the corresponding burden, TEC is a citric acid ester approved as E1505. The industry is switching from one to the other for that reason, and it has nothing to do with longevity.
Is it true that fixation follows Raoult's law?
Partly. A non-volatile substance lowers the mole fraction of the volatile components and thus their partial pressure – the direction is right. But Raoult's law describes ideal solutions, and a perfume composition is not ideal. Hydrogen bonding and interaction with the skin are also in play.
How much physical fixative should be used?
By the Amerchol patent, 0.5 to 5% of the alcoholic or aqueous portion, preferably 1–2.5%. For comparison, the Dragoco patent allows perceptual fixatives such as Timberol 1 to 25%.
Why use an odourless fixative when labdanum and musks exist?
Because a fixative that smells changes the composition. The Amerchol patent says it directly: classical fixatives “can distort the nature or character of the fragrance being fixed”. An odourless substance prolongs without rewriting.
Is it true that anosmia is linked to fixative power?
That is a hypothesis put forward by Dragoco in 1978, not an established finding. It has, however, survived forty years: the definition of “substantially non-odorous” in Coty's 2021 patent explicitly includes materials deemed anosmic to the majority of people.
Can a fixative save perfume oil?
By the Amerchol patent, yes. In a cologne the oil share was reduced from 5% to 4% and 2% fixative added; 85.7% of panelists judged the result equal or better. Qualification: these are self-reports from 1979, not instrument measurements.
Sources
- US 4324703 A – Polyol fragrance fixatives, Amerchol Corp, 1982
- US 4252986 A and US 4313855 A – Fixative for perfume compositions, Dragoco Gerberding, 1981–1982
- WO 2021/247838 A1 – Fragrance composition comprising a fragrance component and a non-odorous fragrance modulator, Coty Inc, 2021
- W. Sturm, K. Peters, “Perfumes”, Ullmann's Encyclopedia of Industrial Chemistry
- CRC Handbook of Chemistry and Physics, 95th edition – boiling points
- PubChem, CID 6781, 6506, 8042