What is a fixative in perfume?

A fixative is a slow material: a base note that evaporates so gradually that it stays on skin for hours and holds a little of the lighter materials back with it. Musks, ambergris materials, resins, balsams, vanillin and the dry woods all do this. A fixative lengthens a perfume that already has a base. It cannot make a citrus top last all day, and it is not a separate product added at the end.

What does a fixative actually do?

Two things, and the first matters far more than the second. It is itself a long-lasting smell, so something is still there when the top notes have gone. And because it sits in the same film on skin as the lighter materials, it slows a small part of them down. Most of what people call fixation is the first effect: the base is still audible at hour eight.

The catalog shows this as strip life, how long a material stays readable on a paper blotter. Ambroxan, Vanillin and Labdanum absolute carry a figure of 400 hours on paper, more than two weeks; Iso E Super carries 280 hours. A citrus oil is gone from the same strip in a few hours. That gap, not any special property, is what a fixative is.

Which materials work as fixatives?

The slow, audible ones from the base of the pyramid. Most of them are called fixatives or base notes in their own catalog notes:

• Musks. Galaxolide can form a large share of a formula as a fixative bed; Ethylene Brassylate is a forgiving smoothing musk; Exaltolide and Ambrettolide are classic fixing musks with more lift. Use two of different chemistry, because many people cannot smell a single musk.
• Ambergris and woody ambers. Ambroxan is radiant and very long-lasting and is usually weighed from a 10 percent dilution. Iso E Super is quiet (2 out of 10 on the catalog's strength scale) and stays for days.
• Resins and balsams. Labdanum absolute, Benzoin Siam resinoid and Tolu balsam are the amber fixatives; the classic amber base is labdanum, benzoin and vanillin together.
• Roots and woods. Vetiver Essential Oil and Patchouli Essential Oil are the natural base notes the catalog calls fixatives.
• Sweet and salicylate materials. Vanillin and Coumarin are the sweet, lasting base of ambers and fougeres; Benzyl Salicylate is barely smelled by many people, yet the catalog calls it the great fixative of tuberose, gardenia and ylang accords.

What can a fixative not do?

It cannot make a top note last. A lemon oil leaves skin at the rate a lemon oil leaves skin, and a fixative slows it only a little. Add a fixative to an all-citrus formula and you get a citrus that vanishes on time, followed by a faint musk that was never part of the idea. The better question is what the perfume should smell like at hour eight, and the answer is a base material you would be happy to wear alone.

It also cannot be added without limit. Too much base makes a perfume dense. In PerfuMate's wear model a material counts as a heavy base once it lasts about 20 hours on skin, and once heavy bases pass about 45 percent of the concentrate, the top and heart start to go muffled: the perfume lasts, but it opens dull.

How much fixative should I use?

Enough for the base to be heard, dosed by the job each material does. Figures here are shares of the concentrate, before alcohol:

• Clean musks: roughly 5 to 20 percent. How to use musks has the detail.
• Iso E Super: from a trace to 5 to 15 percent as a heart and base support. How much Iso E Super.
• Ambroxan and other strong ambers: small amounts from a 10 percent dilution, raised by trial.
• Resins, balsams and vanillin: enough to hold the drydown without turning it syrupy; smell the next-morning strip before raising them.

Raise one fixative at a time and judge it on a dated strip at four hours and the next morning, not in the first minutes. Your own nose adapts to a base long before other people stop smelling it.

Are there odorless fixatives?

A few, and they are weighed as formula lines like anything else. Glucam P-20 is sold to slow the evaporation of an alcohol perfume and is typically added at 1 to 5 percent of the concentrate. Triethyl citrate is a solvent with a mild fixing effect, and Benzyl benzoate a solvent with fixative value in balsamic bases. None of them adds a smell, so none of them gives the drydown an idea. They help a formula that already works.

Do fixatives have IFRA limits?

Several do. Coumarin, Benzyl Salicylate and Benzyl benzoate each have a Category 4 standard of their own and are EU-declarable allergens, Iso E Super falls under the OTNE standard, and some balsams carry restrictions through what is in them. See coumarin, benzyl salicylate, Iso E Super and Peru balsam. A base that fixes well can still be the line that fails, especially in a strong perfume.

PerfuMate gives every material a strip life, draws the drydown so you can see what is still audible at each hour, and runs the IFRA check while you compose, so a heavier base is weighed against its limits as you add it. How to make a perfume last longer takes the question further. Start a formula, free.