Why We Use the Resin: Frankincense, Boswellic Acids, and What Distillation Leaves Behind

Almost every skincare product that says frankincense on the front means the essential oil. That is a real ingredient and a beautiful one, but it is not the whole plant, and it is not the part I want most. This is the long version of why our labels read Boswellia Carterii (Frankincense) Resin.

What frankincense actually is

Frankincense is not a flower, a leaf or a seed. It is an exudate: the hardened sap that seeps out when the bark of a Boswellia tree is scored. The tree is wounded, it weeps, and the tears harden in the sun into the pale gold lumps that have been traded for four thousand years.

Chemically, a tear of frankincense is three things at once. Roughly a third of it is a water-soluble gum — polysaccharides that will dissolve in water and not in oil. A small fraction, usually somewhere under a tenth, is volatile essential oil: the light aromatic molecules that give frankincense its smell. And the rest, the largest part, is the resin proper. That is where the boswellic acids live.

What steam distillation can and cannot carry

Essential oil is made by steam distillation. Steam is passed through the plant material, it picks up whatever is volatile enough to travel with it, and the vapour is condensed back into liquid and separated. It is an elegant process and it does exactly one job: it collects the light, evaporable fraction.

Boswellic acids are not light. They are pentacyclic triterpenic acids — large, heavy, oil-loving molecules with a molecular weight around 456. They do not evaporate at the temperatures a still reaches. They cannot ride the steam. When the distillation is finished, they are still sitting in the spent resin at the bottom of the vessel, and they are not in the bottle.

This is not a controversial point or a marketing angle. It is simply what distillation does. Frankincense essential oil is rich in monoterpenes such as alpha-pinene and limonene, and in some species the diterpene incensole and its acetate. It contains, to a first approximation, no boswellic acid at all.

The same is true of frankincense hydrosol, which is the water that comes off a distillation. Hydrosol carries the water-soluble aromatic fraction. It is a lovely thing in its own right — we use it as the base of our Peptide Face Mist, and the mist is honest about being a hydrosol product — but it is not a boswellic acid product either, and I would not claim it was.

Infusion is the only method that extracts them

Boswellic acids are lipophilic. They will not dissolve in water, but they will move into fat. That leaves two routes: a solvent or supercritical extract made in a laboratory, or a slow infusion into a carrier oil.

We do the second. Whole resin tears, broken down and steeped in organic jojoba, left for six weeks. Jojoba is technically a liquid wax rather than a true oil, which is part of why it works here: it is extremely stable, it will not go rancid over a long maceration, and it is the closest of all plant materials to the skin's own sebum, so what it has picked up gets carried in rather than sitting on top.

Six weeks is not an arbitrary number. Resin is hard and it gives up its constituents reluctantly. A week gets you scent. Six weeks gets you the colour, the weight, and the faintly sticky resinous character that tells you the oil is carrying more than perfume.

The honest trade-off: an oil infusion is gentler and less efficient than an industrial extract, and it is not standardised to a percentage the way a laboratory extract would be. I would rather tell you that than imply a precision we do not have. What I can tell you is that the fraction is there, because infusion is the method that brings it across, and distillation is the method that leaves it behind.

Why it matters for skin that is changing

Boswellic acids are the most studied constituents of frankincense, and the great majority of that research has nothing to do with skincare. I am not going to borrow conclusions from that work and apply them to a face oil, because that is not how evidence transfers.

What is worth saying is narrower. A small controlled study published in 2010 used a cream containing standardised Boswellia extract on one half of the face and a base cream on the other, in a group of women over thirty days, and reported improvement on the treated side in the appearance of fine lines and in measured skin roughness and elasticity. It is one small study. It is not proof. It is, however, the reason the resin fraction is interesting to a formulator rather than only to a perfumer.

In our own products the effect is the one you would expect from a well-made infused oil: skin that looks firmer and smoother, texture that looks more even, and a finish that feels toned rather than merely greasy. That is a cosmetic claim and I am keeping it a cosmetic claim.

The other reason we infuse: scent

There is a second thing the resin gives you, and it is the reason the infusion goes into the Frankincense & Myrrh soap as well as the oils.

We do not use fragrance oils. Anywhere. Everything in the range is scented with essential oils and our own infusions, which is harder, more expensive, and much less predictable than buying a bottle of synthetic frankincense accord. Essential oil alone gives you the bright resinous top note and very little underneath it. The resin infusion gives you the weight: the low, warm, slightly balsamic part of frankincense that stays on the skin after a bar has rinsed away.

So in the soap, the infusion is there for the scent, and that is exactly what I will claim for it. A wash-off product cannot do what a leave-on oil does, and I am not going to pretend otherwise.

Where you will find it

The six-week whole-resin infusion goes into the Firm & Lift Face Oil, the Nourish Body Oil, the Nourish Body Butter, the Nourish Sugar Scrub and the Frankincense & Myrrh Soap.

The bath bomb is scented with frankincense essential oil, and the Peptide Face Mist is built on frankincense hydrosol. Those are good products and I am proud of them, but they are not carrying boswellic acids, and you will not find me saying they are.

Knowing which is which is, I think, the whole point.