A bottle of massage oil is mostly carrier oil; according to the dilution table in the library, essential oils for the body usually sit at only 2 to 5 percent. So the slip under the hand, the speed of absorption and the layer left on the skin are decided almost entirely by the carrier. Sweet almond, jojoba and fractionated coconut look alike in the bottle, but they are three different kinds of molecule. This piece follows the structure of each oil to see why they touch the skin differently.
Triglycerides and wax esters
Almost every plant oil is a triglyceride. The library's vegetable oils page describes this structure as one glycerol molecule bound to three fatty acids. The character of an oil comes mainly from the ratio of those fatty acids: saturated ones such as palmitic and stearic give a solid or thick texture at room temperature, unsaturated ones such as oleic, linoleic and linolenic give a liquid.
A wax ester is another kind. There is no glycerol in the middle; instead, one long chain fatty acid is joined directly to one long chain fatty alcohol through a single ester bond. The result is a straight, long molecule with two arms instead of three. Beeswax and the wax coating many leaves also contain plenty of wax esters, alongside other components such as hydrocarbons and free fatty acids.
The three carriers in this piece therefore fall into two groups. Sweet almond and fractionated coconut are both triglycerides, but with fatty acids of very different lengths. Jojoba stands apart, as a wax ester. Almost every difference in feel and stability between the three begins here.
Jojoba: a wax in liquid form
Jojoba, Simmondsia chinensis, is a shrub of the North American desert. The library records that jojoba oil is actually a liquid wax ester, not a triglyceride, and that its structure is close to the natural sebum of human skin. A 2021 review gives jojoba as almost 98 percent wax, mainly wax esters of long chain fatty acids and alcohols, with a little free fatty acid, fatty alcohol and hydrocarbon.
The main fatty acid in jojoba is 11-eicosenoic acid, a 20 carbon chain with one double bond, at about 70 to 77 percent depending on the analysis; then erucic acid, 22 carbons, at about 12 to 14 percent, and oleic at about 9 to 10 percent. The figures shift with soil and climate, but the overall picture holds: long chains, each with only one double bond.
It is called a wax because of its structure, not its hardness. Jojoba only solidifies at about 7 to 10°C, so in the Vietnamese climate it is always liquid. Few triglycerides, few double bonds and the natural tocopherol the library mentions make jojoba very resistant to rancidity: the library records a shelf life of 5 years or more, the longest in its table.
The piece on an oil for neck and shoulders chose jojoba as its main carrier because it dries quickly and leaves no greasy feel. The library's carrier oil map also places jojoba at the fastest absorbency level, even though its structure is a wax.
Sweet almond: oleic and linoleic
Sweet almond, Prunus dulcis, is a typical triglyceride built from 18 carbon fatty acids. The library table records oleic at 60 to 78 percent, linoleic at 17 to 25, linolenic below 0.5 and saturated at 6 to 10. In other words, almost the whole oil is unsaturated fatty acid, most of it with a single double bond.
Each cis double bond bends the carbon chain at an angle. Bent chains cannot pack tightly together, so the oil is liquid at room temperature. The library notes that oleic gives an oil a balanced feel, moderate absorption and good oxidative stability; linoleic, with two double bonds, gives a drier feel and faster absorption, but oxidises faster.
Sweet almond carries both, with oleic in the lead. The library places it among the balanced oils, which absorb moderately and leave a light emollient layer, the group used for body oils and massage oils. The library also notes that it suits most skin types except for people with nut allergies, and that its shelf life is about 1 year.
All three formulas in the piece on three body oils for the dry season include sweet almond, each at a different proportion. That is the familiar role of this oil: a soft, liquid, easy to combine oil standing between two extremes.
Fractionated coconut: the liquid part of a solid fat
Coconut oil, Cocos nucifera, has 85 to 92 percent saturated fatty acids according to the library. In its virgin form the oil is solid below 24°C, rich in lauric acid and smells of coconut. The fractionated form is quite different: the library records it as a permanently liquid oil, MCT separated and odourless.
MCT stands for medium chain triglycerides. In production, the fatty acids with 8 and 10 carbons are separated from the longer chains, including most of the 12 carbon lauric, and then joined back onto glycerol. The result is mainly triglycerides of caprylic acid, 8 carbons, and capric acid, 10 carbons; supplier specifications usually give lauric below 3 percent. On a cosmetic ingredient list this part usually appears as Caprylic/Capric Triglyceride.
This is the interesting point in the chemistry: an oil that is almost entirely saturated, yet liquid. Saturated chains usually pack tightly and make a fat solidify, but chains of 8 and 10 carbons are too short to create strong enough attraction between molecules. With no double bonds, the oil also leaves almost nowhere for oxygen to attack; the library's shelf life table has only a general coconut row, 2 to 4 years, while supplier specifications for fractionated coconut usually give 24 months.
Absorption and feel on the skin
The library has a carrier oil map whose vertical axis is absorbency, from 1 for the slowest to 5 for the fastest. Jojoba sits at 5, fractionated coconut at 4, sweet almond at 3. For comparison, virgin coconut sits at 2, olive and shea butter at 1. It is a relative scale between oils, not an absolute measurement.
The library explains that skin feel relates directly to the ratio of linoleic to oleic and to molecular polarity. Dry oils absorb fast and leave no greasy film; balanced oils absorb moderately and leave a light soft layer; greasy oils absorb slowly and leave a heavy film. The library places sweet almond and jojoba in the balanced group.
Fractionated coconut is light for a different reason: its molecules are much smaller than those of the other two, its fatty acid chains only half as long, so the oil is thin: the technical sheet of one Caprylic/Capric Triglyceride gives a viscosity of about 30 mPa·s at 20°C. The three oils therefore do not line up in a row; they cover three different points: a long chain wax that absorbs fast, a short chain triglyceride that is thin, and a long chain triglyceride that absorbs moderately.
Lê Mai's Chilling Massage Oil No.082 uses exactly these three oils: a base of sweet almond, jojoba and fractionated coconut, with white tea essential oil, Camellia sinensis from the leaf, sourced from India. White tea leads, a light, clean tea note. Fractionated coconut is nearly odourless and jojoba has only a very faint scent, so that light tea note is not covered by the base.
Double bonds, oxygen and essential oils in the base
The library records that plant oils go rancid through oxidation at the double bonds of unsaturated fatty acids: linolenic with three double bonds goes fastest, linoleic with two sits in the middle, oleic with one is slow. Fractionated coconut has almost no double bonds. Jojoba has one double bond on each long chain. Sweet almond carries 17 to 25 percent linoleic, so it is the link oxygen reaches most easily among the three.
In a blend, the stability of the whole bottle is usually set by its least stable component. The library records a shelf life of about 1 year for sweet almond, 5 years or more for jojoba, 2 to 4 years for coconut in general. The library also notes that vitamin E, tocopherol, is a natural antioxidant present in many oils and is often added at 0.5 percent to extend shelf life.
The carrier is also the solvent of the essential oil. As the two percent piece explains, the diluent for essential oils has to be a fat; water only disperses them into temporary droplets. The aroma molecules dissolve into the spaces between the fatty acid chains, then evaporate gradually from the thin layer of oil on the skin.
Serenity Massage Oil No.026 places Rosa damascena rose oil on a base of cold pressed plant oils, with the rose sitting in the middle of the scent, light and close. Relaxation Massage Oil No.052 uses cold pressed plant oils with lavender essential oil, Lavandula angustifolia, from Bulgaria, a classic, cool floral. The names of the two bottles are names of scents; what touches the skin is the carrier.
Two of the oils are triglycerides, one is a wax.
Short chains make coconut light, double bonds make almond soft, a single ester makes jojoba durable.
The essential oil gives the bottle a scent; the carrier gives the hand a feel.