What are essential oils?
An essential oil is a concentrated hydrophobic liquid containing volatile aroma compounds from plants. They are often referred to as essence or oil of a specific plant, such as essence of lavender, or clove oil. Essential oils, like all organic compounds, are made up of hydrocarbon molecules and can further be classified as terpenes, alcohols, esters, aldehydes, ketones and phenols etc. (As henna artists we are most interested in specific terpenes called monoterpene alcohols, but we’ll get back to that a little later.) In plants these chemicals are naturally created as means of communication with other plants, to attract species that are helpful, and to repel those that are harmful. The also play varied rolls in plant metabolism. Its just by chance that humans are able to take advantage of them for medicinal purposes, as scents and flavorings, and to give a boost to henna paste.
Essential oils are made from the plant parts in three basic ways. (There are variations on each of these three methods. For more in depth information please see the resource list below.) Steam distillation is the most common method as its simple and cost effective. Heat is applied to the plant matter until the volatile liquid in the plant are vaporized, then condensed back into a liquid. Expression is a method reserved for citrus oils. With citrus fruits the essential oils are concentrated in little pockets between the skin and the fruit. The skins are pressed to release this oil, it and any juice are caught, and the juice is separated from the oil with a centrifuge. The last method, solvent extraction, is costly but necessary where some plants with very delicate oils would be damaged by steam distillation, such as with jasmine, rose, and some others. CO2 extraction produces the highest quality of oils produced this way, and will not have traces of solvents as some of the other solvent extraction methods may. Realistically though, for most people any oils produced by extraction will be far to expensive to use in henna paste.
Its also important to note here what essential oils are NOT. Using a fragrance oil, or an essential oil diluted for aromatherapy or massage purposes will not improve henna stains one bit! Fragrance oils are man made, synthesized chemicals made just to smell like something. They do not have all the fine complexities of real essential oils. Often the part of an essential oil useful in improving henna stain doesn’t play much of a roll in the overall scent and wouldn’t be a part of the man-made counterpart. Also many fragrance oils contain phthalates or other chemicals that health conscious people may want to avoid. Another category of oils that are not helpful to henna artists are oils diluted for aromatherapy use. Most oils (with some exceptions like tea tree or lavender) are not recommend for “neat,” or direct undiluted use on the skin because they are too strong when used that way. Often oils intended for aromatherapy will be sold already diluted by a fixed oil such as grape seed oil or sweet almond oil. These oils will not be concentrated enough to work on paste. Pure oils added to paste are effectively diluted by the other ingredients in the mix so that they are still mild enough for use on skin.
How do essential oils help improve stain?
Essential oils dissolve lawsone molecules into a an evenly dispersed solution. Think of adding salt to water, and how once dissolved, each sip or drop of water will have the same amount of salt. Not only that, but in solutions materials have a more loose chemical structure that will make the lawsone more available to attach to skin. Lawsone, however is not water soluble so juice, tea, or water will not get the job done. It can be dissolved in things like kerosene or turpentine, but those ingredients would be horrible for our uses! These are dangerous chemicals! Henna artists need something that is skin safe and healthy for humans that will also dissolve the lawsone. Of all the hundreds, and hundreds of possible chemical constituents naturally present in essential oils, monoterpene alcohols are some of the most useful. They tend to be mild, nontoxic, effective against microorganisms, and have a tonifying effect. This means that they are often used in skin care and hygiene. As luck would have it they are also effective solvents for our purposes! Adding one to two tablespoons (15-30 ml) of essential oils high in monoterpene alcohols per 100 g of henna powder will dissolve lawsone in paste and greatly increase its ability to absorb into skin and bind to proteins there.
There are some traditional uses of oils that are non-helpful wive’s tales. Applying oils to the skin before applying henna designs is not effective at all. In fact using essential oils “neat” or un-diluted directly on skin can be very irritating and using oils cut with fixed oils can seal skin away from the paste, blocking absorption of the lawesone dye. Applying essential oils after the paste is removed is also not helpful. It may be useful, however, to use olive oil or other cooking oil to help loosen paste and remove residue rather than washing with water, and it may be helpful to apply oily products like lotion, lip or body balms, or even olive oil to skin before showing or bathing to seal the skin away from water and to help discourage exfoliation.
Which essential oils are safe and effective?
Common monoterpene alcohols include carvacrol, linalool, citronellol, geraniol, alpha-terpinol and terpinol-4, thymol, menthol, cineol, eugenol. Some of these can be irritating to skin when the are heavily present in an essential oil though! Of these those that are non irritating and and effective are lilalool, both terpinols, geraniol, ceneol, and cedrol. Tea tree has cineol. Cajeput and Niaouli both have high levels of cineol and terpineol. Geranium has geraniol and linalol. Clove has high levels of eugenol.
There’s more to it than just identifying these chemical constituents. Just because an oil contains the good monoterpene alcohols, doesn’t make it a good oil for paste! Camphor, for example, is full of cineol and terpineol, BUT its also toxic because of other chemicals naturally present in the oil. Also, plants with similar names are NOT equal. Clove bud makes a perfectly fine paste enhancing essential oil (although can be irritating to some, so use it in small amounts) but clove leaf is a strong irritant! You should also know that sometimes essential oils are improperly labeled. Eucalyptus Globulus is a great “terp” (slang term for essential oils high in monoterpenes and and skin safe for use in henna paste) but other varieties are not. Its common to find eucalyptus essential oil labeled “globulus” that turn out to be a different variety all together! Quality can be a serious issue too. Depending on how the oils are distilled, toxins involved in the extraction can be left behind. To complicate the issue even further many companies will use the term like “aromatherapy grade,” which are essentially meaningless. Some multi level marketing companies will supply their representatives with credentials that are without any value or authority to help them sell over priced, poor quality product. Be wary of this practice! One last thought on oil choices: Even the same species of plant can be different from one source to the next. Lavender is a perfect example. Even though they are all True Lavender, lavender from France (or fine lavender) has much lower levels of monoterpene alcohols that that grown in Hungary or Bulgaria. When shopping for essential oils for your henna paste it is really best to shop with a dedicated henna supplier. They know all these details including the ones that don’t effect other consumers.
Please be careful and responsible in your use of essential oils. Some oils can be dangerous for people with specific medical conditions. Lavender is very mild and a good choice for people who are pregnant, ill, or have very sensitive skin. Choosing good, safe, and effective essential oils for use in henna paste requires a lot of trust in a supplier, or a lot of independent research. Always be very careful in your choice and make sure that you clients are well aware of the ingredients in your paste.
Sources and further study:
The Illustrated Encyclopedia of Essential Oils, Julia Lawless
Advanced Aromatherapy: The Science of Essential Oils, Kurt Schnaubelt
The Usborne Illustrated Dictionary of Chemistry, Jane Withereim, et al
Fixed oils– Vegetable oils that do not evaporate easily such as olive oil, sunflower oil, coconut oil. These oils are often plant derived but are not essences.
Lawsone– The dye in henna. Also called hennatonic acid, or natural orange 6
Volatile– Evaporates easily
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