α-Humulene

Aroma and sensory profile

Alpha-humulene is quiet on its own. Fragrance references type it woody and describe the neat material simply as woody [1]; a perfumery classification places it among warm spices with cinnamic, almondy, and balsamic facets [2]. In hops it is the earthy, herbal counterweight to myrcene's fruit and resin, which is why hop varieties rich in humulene read as "noble" rather than tropical. Its bitterness is a beer-drinker's association with the hop rather than a property measured in the pure compound.

The molecule is the ring-opened isomer of beta-caryophyllene: the same fifteen carbons and the same formula, C15H24, arranged as an eleven-membered ring with three double bonds instead of the fused four- and nine-membered rings [3]. It has no stereocenter, only fixed E geometry at each double bond, so there are no enantiomers to compare and no mirror-image forms with different odors [3]. The two isomers travel together in nature, which is why clove, pepper, and copaiba carry both.

Effects and research

No human trial of alpha-humulene was found in the sources reviewed. The evidence is animal.

The strongest work comes from a Brazilian group studying Cordia verbenacea, a medicinal shrub whose essential oil yields both alpha-humulene and trans-caryophyllene. Given orally at 50 milligrams per kilogram, alpha-humulene markedly inhibited carrageenan-induced paw edema in mice [4]. In a companion study it reduced paw edema induced by platelet-activating factor, bradykinin, and ovalbumin, largely prevented tumor necrosis factor-alpha and interleukin-1-beta generation in carrageenan-injected rats, and, with caryophyllene, reduced prostaglandin E2 production and the expression of inducible nitric oxide synthase and cyclooxygenase-2 [5]. In an allergic asthma model, female mice sensitized to ovalbumin received alpha-humulene at 50 milligrams per kilogram orally or 1 milligram per milliliter by aerosol; both routes significantly reduced eosinophil recruitment and lowered IL-5, CCL11, and leukotriene B4 in airway fluid [6].

These are consistent anti-inflammatory results across several models, and the aerosol arm is unusual in showing an effect by inhalation. They remain rodent data at doses far above dietary exposure. Alpha-humulene has no known cannabinoid receptor activity; the CB2 binding that distinguishes beta-caryophyllene depends on the ring the humulene isomer lacks, and no study reviewed here reports it for humulene.

Natural sources

Hops are the defining source, and the name comes from the plant, Humulus lupulus. In a 2025 analysis of steam-distilled oils from fresh hop cones, alpha-humulene ran from 19.52 to 24.98 percent of the oil, the largest sesquiterpene fraction, behind only myrcene overall [7]. Clove bud oil carries it in the 10 to 40 percent of the oil that is not eugenol, alongside eugenyl acetate and beta-caryophyllene [8]. Cordia verbenacea, the Brazilian medicinal shrub behind the anti-inflammatory studies, yields it in useful quantity from its essential oil [4][5]. Beyond these, a perfumery reference notes it in a countless number of essential oils, usually in trace amounts, across spices, herbs, woods, and citrus [2]. It is a regular minor constituent of cannabis, where it accompanies beta-caryophyllene in most chemotypes.

Boiling point and vaporization

No atmospheric boiling point for alpha-humulene meets this site's source standard. PubChem's only published value is 99 to 100 °C at 3 mmHg, a vacuum-distillation figure [3], and the atmospheric numbers that circulate in terpene charts, including the 198 °C this site once carried, trace to no primary source. This profile therefore lists none. What can be said is structural: as a fifteen-carbon sesquiterpene it belongs with beta-caryophyllene among the least volatile terpenes, far above the monoterpenes that boil between 155 and 200 °C, which is why humulene's earthy hop character survives a long boil in the brew kettle while myrcene is driven off, and why it is among the last compounds to leave any heated product. No thermal degradation study of alpha-humulene was found.

Safety and regulation

Alpha-humulene sits in a regulatory gap that beta-caryophyllene does not. It is absent from the US Food and Drug Administration's list of permitted synthetic flavoring substances at 21 CFR 172.515, where beta-caryophyllene, caryophyllene alcohol, and caryophyllene oxide all appear [9]. Its dietary presence in hops, clove, and other foods is long-standing and unrestricted, but no fetched source establishes a formal flavoring listing for the isolated compound. No cancer classification applies, and no skin sensitization study of alpha-humulene or its oxidation products was found among the sources reviewed, unlike the well-studied hydroperoxides of limonene and linalool. The animal studies above used oral doses of 50 milligrams per kilogram without reported toxicity, which says nothing about long-term human safety at any dose.

Industries and uses

Culinary: alpha-humulene is central to beer, where hop varieties with high humulene contribute the earthy, herbal character brewers describe as noble, and its low volatility keeps that character through the boil in a way myrcene's does not [7]. Fragrance: it is a minor woody, warm-spice material, more often present as a natural constituent of clove and other oils than dosed on its own [1][2]. Aromatherapy: clove oil and the Cordia verbenacea oil studied for inflammation are its practical carriers; the aerosol result in mice is the only inhalation evidence [6][8].