Frankincense essential oil, the resin that became a home scent

In short

• The resin is tapped from the bark and hardens into tears; the oil is what the still takes out of them.
• Boswellia sacra and carterii give the classic lemon-and-pepper scent, serrata is sharper and greener, frereana softer and sweeter.
• It is a base note: two or three drops under citrus, lavender or cedarwood suit a winter evening in the living room.

How the resin is tapped and the oil is made

Frankincense, or olibanum, starts as a milky sap. Harvesters cut small wounds in the bark of a Boswellia tree, which grows in dry country in Oman, Somalia, Ethiopia and India, and the sap hardens on the trunk into pale lumps called tears.

Burning the tears on a hot coal is incense, the smoke you know from a church. For the essential oil, crushed resin goes into a still, steam carries the lighter, scented part out of it, and the oil is drawn off the cooled water. The heavier part of the resin stays behind, so the oil smells cleaner than the smoke.

The four Latin names you will meet on a bottle

The species decides much of the scent, and a careful seller prints it on the label. These are the four you are most likely to see.

Sacra and carterii are so alike that many sellers treat them as one tree; either is a safe first bottle. Serrata is usually the cheapest, frereana the sweetest.

What it does once the diffuser is running

The first minutes are the lemon-and-pepper top. That lifts off, and what settles in the room is the dry, woody, faintly sweet base. Frankincense is a base note: it leaves the bottle slowly and stays in the air long after a bergamot has gone.

On its own it can read a little solemn; under a lighter oil it holds the blend together and keeps the room scented through the evening. A low, steady output suits it best, and noise matters once the room is quiet; our comparison of electric diffusers on noise and running cost covers both.

Three partners, and one for December

• Sweet orange or bergamot. The citrus lifts, the frankincense gives it somewhere to land; the most forgiving pairing.
• Lavender. Softens the resin and takes the edge off the pepper; many people find it the gentler choice for a bedroom.
• Cedarwood. Dry on dry, so the room smells of warm wood rather than perfume; good in a hallway or study.
• Sweet orange with a single drop of clove or cinnamon leaf. The run-up to Christmas in three bottles.

Let frankincense be the smaller share to begin with, two or three drops under a few of the partner oil. A blend that smells right at the door can feel heavy an hour later.

The rooms and the months it suits

Frankincense is an evening oil and a cold-weather oil. It suits the living room once the lamps are on, a study on a dark afternoon, and the hallway in December. It is less at home in a kitchen at breakfast, and a small bathroom is soon overdone.

Because it lingers, set it going before you sit down and switch it off when you leave the room. Room size matters more for a base note than for a citrus, so our table of stated room size and refill cost per diffuser is worth reading before you choose a machine.

Telling a pure oil from a frankincense fragrance

Turn the bottle round. A pure oil names the species in Latin, says steam distilled, and gives a country of origin and a batch number. Frankincense with no Latin name and no country is a reason to put it back.

A frankincense fragrance oil is a composed scent with parfum or aroma oil in the ingredients and may contain no resin at all. It is fine on reeds or in a burner and the wrong fill for a machine built for essential oils; our guide to which electric diffusers run on loose oil and which on pods explains what each machine accepts. A bottle at the price of lemon oil is usually serrata, a dilution or a fragrance oil.

An oil that goes off, and the usual cautions

The bright top of frankincense is the part that goes off: it reacts with air, and an old bottle smells sharp and turpentine-like rather than lemony. Dark glass, a cap done up straight after use and a cool cupboard slow that down.