Guaiol

Aroma and sensory profile

Guaiol is the quiet heart of guaiacwood oil. Fragrance references type it woody and describe (−)-guaiol neat as mild guaiacwood and tea rose [1]. The oil it comes from is fuller: sweet, dry, woody, spicy, powdery, balsamic, tea rose, oriental, and copaiba-like, a thick paste at room temperature that has to be warmed to pour [2]. Where most woody terpenes lean toward cedar or pine, guaiol leans toward rose and tea, a soft, slightly smoky, almost lactonic wood that perfumers use to round out floral and oriental bases.

The molecule is a bicyclic guaiane sesquiterpene alcohol with three stereocenters and it is chiral. The natural material is (−)-guaiol, and every pharmacology paper below uses that form; no panel description of (+)-guaiol was found and it is not reported from plants, so no claim about how the two enantiomers differ is made here. Guaiol is a solid, melting at 91 to 93 °C [1], which is why guaiacwood oil sets into a paste and why a cannabis extract rich in it can look waxy.

Effects and research

No human trial of guaiol was found. The literature has three threads, none of them about mood or inhalation.

The first is ecological. Guaiol isolated from Ferula ferulaeoides was a contact and fumigant insecticide, with an LD50 of 0.07 milligrams per larva against Mythimna separata, 8.9 milligrams per larva against diamondback moth, and fumigant LC50 values of 3.5 and 16.9 microliters per liter against armyworm and housefly, plus aphid inhibition at 70 milligrams per liter [5]. Against Leishmania amazonensis, guaiol from Aloysia gratissima oil had an IC50 of 0.01 micrograms per milliliter on amastigotes while remaining safe to macrophages up to 100 micrograms per milliliter [6].

The second is oncology, in cells and mice. (−)-guaiol suppressed non-small cell lung cancer growth by destabilizing the DNA repair protein RAD51 through autophagy, causing double-strand breaks and apoptosis [7], and later work found it triggered immunogenic cell death, increasing dendritic cell activation and T-cell infiltration in tumors [8]. Several follow-up papers place the mechanism on PPAR-gamma and macrophage polarization.

The third is pharmacokinetic. After oral Ferula extract in rats, guaiol reached a peak plasma concentration of 28.6 nanograms per milliliter at 30 minutes with a half-life of 9.2 hours, so it is absorbed and persists [9]. None of this has been tested in people.

Natural sources

Guaiol is a wood terpene. Its commercial source is guaiacwood oil, steam-distilled from the heartwood of Bulnesia sarmientoi, a tree of the Gran Chaco of Paraguay and Argentina [2]; a gas chromatography study of that oil found guaiol at 48.3 percent alongside 2-undecanone [4], and fragrance databases log it at 26.8 percent in a commercial sample [1]. The Australian cypress pines are the other rich source, with Callitris columellaris wood oil at 14.6 percent, Callitris intratropica at 13.7 percent, and Callitris glaucophylla at 6.2 percent, followed by ayou wood at 3.4 percent, Cassinia flower oil at 2.2 percent, Helichrysum at 1.7 percent, and cajuput at 1.2 percent [1]. Ferula ferulaeoides and Aloysia gratissima carry it as a major sesquiterpene in their oils [5][6]. In cannabis guaiol is a minor sesquiterpene that a few chemotypes carry at noticeable levels.

Boiling point and vaporization

No atmospheric-pressure boiling point for guaiol appears in PubChem or in a primary paper found for this profile, so none is listed. The 92 °C figure this site previously showed was guaiol's melting point, 91 to 93 °C, mislabelled as a boiling point [1]. Fragrance references quote 309 to 310 °C at 760 mmHg [1], an industry value not adopted here. What can be said is that guaiol is a fifteen-carbon alcohol and a crystalline solid, less volatile than any monoterpene or hydrocarbon sesquiterpene on this site; it does not vaporize from a warm sample so much as melt into the oil around it and stay there. PubChem records no experimental boiling point for it at all [3]. No thermal degradation study of guaiol was found.

Safety and regulation

Guaiol is not listed by name in the FDA synthetic flavoring table, but its acetate ester is, at 21 CFR 172.515 as "Guaiol acetate" [11], and guaiac, from Guaiacum officinale, Guaiacum sanctum, and Bulnesia sarmientoi, is a permitted natural flavoring at 21 CFR 172.510 [10]. The Research Institute for Fragrance Materials assessed guaiacwood acetate, the acetylated oil, in 2022 [12]. No cancer classification applies.

Its hazard record is empty in the best sense. Under Europe's classification inventory, all 234 company reports state that guaiol does not meet GHS hazard criteria, so it carries no signal word and no hazard statement [3]. No sensitization series naming guaiol was found. The only practical note is the one that applies to any solid sesquiterpene alcohol: it is not the fraction of an essential oil that irritates, and a guaiacwood-rich base is among the gentler things a perfumer can put on skin.

Industries and uses

Fragrance: guaiol and guaiacwood oil supply a soft, tea-rose woody base and fixative in floral, oriental, and woody accords [1][2]. Culinary: guaiac is a permitted natural flavoring and guaiol acetate a permitted synthetic one, both used at trace levels for woody, balsamic depth [10][11]. Aromatherapy: guaiacwood oil is its carrier, valued for its hazard-free classification and its persistence on skin [2][3].