By: Leslie Moldenauer, CHNC, HHP, Certified Aromatherapist
Raise your hand, who loves to take a bath? Aromatic baths at the end of the day to de-stress and unwind, there’s nothing quite like it in my book. There is one very specific thing you need to think about before you step into your bath when using essential oils, and that is, are you using a proper dispersing agent? There is a plethora of misinformation floating around the internet and on social media on this topic. I decided to help to clear up any possible confusion. Let’s get started!
Touching On Chemistry
Very briefly, most essential oil molecules consist of carbon and hydrogen. Several contain oxygen, and few contain sulphur and nitrogen. Essential oil molecules have various structures and contain different numbers of bonds, for example monoterpenes have 10 carbon atoms, sesquiterpenes have 15. The types of bonds within a molecule change its structure, odor, therapeutic property, toxicity, and solubility.
Let’s Hone In On Solubility Of Essential Oils
It is important for any essential oil enthusiast to understand what solubility means. Joy E. Bowles stated in her book, The Chemistry of Aromatherapeutic Oils, “For a substance to be dissolved in another substance, the molecules of each substance must freely co-mingle. As a general rule of thumb, polar substances will dissolve in polar solvents, and non-polar substances in non-polar solvents” (1).
From a formulator’s standpoint, solubility is the ability of a solid, liquid, or gas to dissolve in a liquid solvent to create a homogeneous solution (2).
Homogeneous=a solution that is of uniform structure or composition throughout (3).
Essential Oils Are Not Soluble In Water. Why is this?
Essential oils are lipophilic (combine with or dissolve in lipids or fats), also called non-polar substances. In contrast, Epsom salt, sea salt, and baking soda is hydrophilic (mix with, or dissolve in water), also called a polar substance.
Before those well versed in chemistry yells from the rooftops “But salt is ionic”! I am over simplifying here. Ionic substances are VERY polar in nature (more complex, they are metal and non-metal) (4). They are not technically polar molecules, but they are polar in their behavior.
In looking at what Joy stated above, we see that essential oils and water will not dissolve or disperse, they will not freely co-mingle as essential oils are non-polar, and water is polar. The essential oil will float on top of the water. The same would apply for Epsom salt, sea salt, or baking soda; they would dissolve in water but the oil would still stay separate.
Spotlight on Solubizers
Solubizers are a great option for the bath. In this case, solubizers are a substance (a solvent) used to incorporate an oil-based ingredient (a solute) into a water-based product, making them a homogenous solution, or helping them to freely co-mingle (5). A solubizer essentially forces a substance that was not previously able to be soluble in water (essential oil) to properly disperse.
Polysorbate 20, polysorbate 80, and a product called Solubol fall into the category of solubizers, and can be used to disperse essential oils into water and forge that homogenous solution. Of these three, Solubol would be my recommended solubizer. The recommended ratio (before adding to the tub) is 1:4, 1 drop essential oil to 4 drops Solubol.
Spotlight On Surfactants
For ease of explanation, the molecule of a surfactant has one end (head) that loves water and the other end (tail) that loves fat. A surfactant “holds hands” with these two, helping them properly disperse in the bath. In other words, a surfactant helps two substances that do not easily mix together (oil and water), to chemically bond and remain mixed. Therefore, surfactants such as shampoo, soap, or bubble bath, are useful in an aromatic bath. My recommendation is fragrance free shampoo to avoid possible irritation of the urogenital tract. Mix 1tbsp fragrance free shampoo with your essential oil before adding to the bathwater for best results.
Spotlight On Diluents
Following me so far? The last substance that I want to talk about is diluents. For me, these are an added luxury to a bathing experience. Diluents are fat based, and include full fat crème, full fat milk, or carrier oil.
The crème/milk will have a mild dispersing action, whereas the oil will not. We know that carrier oil and essential oil blended and applied topically to the skin works brilliantly, but when we add these two to water, they will float/remain on the top. Carrier oil is acceptable in the bath, but use caution as the tub can get slippery fast (and will need a good scrub when you are done). I prefer full fat crème; one cup is plenty.
I hope that this helps to clear up any confusion in regards to taking an aromatic bath. There are a number of ways that it can be done safely, but salts alone are not enough. If you have any further questions regarding this topic, please reach out to one of Plant Therapy’s on staff aromatherapists at email@example.com.
(1) Bowles, E.J. (2003) The Chemistry of Aromatherapeutic Oils. (3rd Ed) Crows Nest, N.S.W.: Allen & Unwin. (p 45)
(2) Solubilizers: How are they different from emulsifiers? Retrieved from http://swiftcraftymonkey.blogspot.com/2012/06/solubilizers-how-are-they-different.html
(3) Definition of homogenous. Retrieved from https://www.merriam-webster.com/dictionary/homogeneous
(4) Introduction to ionic compounds. Retrieved from http://chemistry.elmhurst.edu/vchembook/143Aioniccpds.html
(5) Fun with chemistry: solubility. Retrieved from http://swiftcraftymonkey.blogspot.ca/2010/03/fun-with-chemistry-so
Leslie Moldenauer, CHNC, HHP, Certified Aromatherapist, has been studying natural living and holistic wellness for over 10 years. Leslie is a trusted resource that covers essential oil safety and encompasses all that natural living has to offer. She is passionate about providing education and tools to help others make decisions regarding safety above all things when utilizing aromatherapy in the home.