While it is common in the “world of aromatherapy” to be encouraged to simply add essential oils to a bath, to a foot bath, or to a compress with only water, you may want to think twice. Let’s discuss why…
Oil & Water… DO. NOT. MIX!
Pure, unadulterated, and undiluted essential oils are ‘hydrophobic’.

Pure, unadulterated, and undiluted essential oils will not disperse in water. Why? Because they are ‘hydrophobic’. In other words, they do not blend with or disperse in water.
Most essential oils are lighter than water and will float on top. There are also certain essential oils that are more dense than water, a few examples being vetiver, cinnamon, and clove. These essential oils will sink to the bottom. Regardless of where the essential oils lie, they will not disperse into the water. By separating to the top or the bottom, they will then adhere to whatever passes through the water like skin, or a cloth that then gets applied to the face, arms, or sensitive parts.
When adding essential oils to water special consideration should be given to children, pregnant women, and the elderly as their skin is much more sensitive than the typical adult.

Essential oils can be especially damaging to mucosal areas of the body and if inadvertently splashed into the eyes. Citrus oils which are relatively mild topically, may become an irritant when used for bathing.
One should also take into consideration that the skin of children, pregnant women, and the elderly is much more sensitive than that of the typical adult.
How to fix this problem?
The answer is to “solubilize” the essential oil prior to putting it in the water. Solubilization is the process of evenly dispersing essential oils throughout the water so they will not either float or sink. The medium used to accomplish this is called an emulsifier.
An emulsifier works because it has two parts, one with an electric charge that dissolves in water but not in oil, and the other part that will dissolve in oil but not water. Emulsifiers that are more soluble in water than oil will form ‘oil-in-water’ emulsions. They blend smoothly with water molecules, something that carrier oils cannot do.

This is exactly what is needed for essential oils, so while you may choose to skip this step for yourself (don’t say I didn’t tell you so), please don’t add essential oils to bath water, foot baths, or compresses for others without first mixing them with an emulsifier.
A very nice option to use as an emulsifier is modified tapioca starch. Modified Tapioca Starch is derived from the starch of the cassava plant while the flour comes from the root of it. When used for food and pharmaceuticals, the starch is treated or “modified” which causes partial degradation. Modified starch is used as thickener, stabilizer, tablet disintegrant, and in the case of mixing oils and water, an emulsifier!
The word modified in this instance does not refer to genetic modification. It refers to the processing required to end up with a product suitable to endure a greater range of temperatures, both heat and freezing temperatures, acidity, increased shelf life, and in this case as an emulsifier. You will want to make sure the product you select is labeled non-GMO.
To prepare, put 2 tablespoons of modified tapioca starch into a small glass bowl. Next, add 5 to 20 drops of essential oil(s) and stir until completely mixed. The amount of essential oil you choose will depend upon the type of oil, the age of the person, and the condition being treated (or whether it is simply for enjoyment.) Then this can be added to the bath.
Castile soap is another option. While some varieties come already scented, Dr. Bronner’s hemp baby soap is unscented and useful for creating your own blends. Mix 5 to 20 drops of essential oil(s) into one tablespoon of Castile soap. Shampoo or body wash may also be used in place of Castile soap.
A third, less-desirable option would be to use a carrier oil or vegetable oil in the same proportions as the Castile soap. The essential oils will be diluted in the carrier, but still float around the top of the water because the carrier will float as well. Regular coconut oil is not recommended as it tends to build up in the pipes after use. Less greasy oils that would make better selections would be fractionated coconut oil and MCT oil.
Substances that are not emulsifiers…
Robert Tisserand, essential oil safety expert recommends that the following items not be used in place of an emulsifier: milk, salt (including Epsom salt), soda, cornstarch, witch hazel, glycerin, or any form of aloe vera. Any clays, including Bentonite clay are also not recommended.
These substances are not emulsifiers. They are all water-soluble and will dissolve once in water releasing the essential oils into the bath. The result will be just as though nothing had ever been used.

…just as though nothing had ever been used.
Although commonly used in cosmetics, pharmaceutical drugs, vaccines, and even food, the following emulsifiers are not recommended.
Polysorbate 20 –
Although polysorbates in their original form are sorbitol, which is a harmless sugar alcohol, when it is used in cosmetics and personal skin care products it is treated with 20 parts of ethylene oxide. At that point it becomes contaminated with 1,4-dioxane which is a known animal carcinogen and likely human carcinogen that readily penetrates the skin and has been connected with skin allergies.
“The Organic Consumers Organization, adopting information from the Campaign for Safe Cosmetics, released a fact sheet on 1,4-dioxane. They report that the levels of 1,4-dioxane found in many personal care products are 1,000 times higher than those found to cause cancer in animal studies. They add that according to the FDA, ‘Skin absorption studies demonstrated that dioxane readily penetrates animal and human skin from various types of vehicles.
This can be especially concerning if you’re taking a hot bath or shower. As your pores open up, your skin could be taking in even more of the 1,4-dioxane in the product.”1
Polysorbate 80 –
One characteristic of polysorbate-80 is that it has the ability to solubilize the blood brain barrier (BBB). We know that it is a skin irritant and eye irritant and hazardous when ingested or inhaled. In mice studies, polysorbate-80 has been found to cause adverse reproductive effects, is mutagenic, and cancer-causing on animals. Unfortunately, there does not appear to be human data available. It is considered safe while virtually untested on humans.
Dr. Randy Baker, Holistic Medicine, University of Michigan Medical School says “I consider polysorbate 80 moderately toxic; while occasionally eating it will not kill you, it may be a carcinogen, aggravate colitis, cause allergies, aggravate cardiovascular disease etc. It depends on how much you ingest but it’s best to minimize all processed foods and emphasize whole organic foods.2
While the Polysorbate 80 molecule is considered too large to penetrate the skin, external use as an emulsifier may be an option if one of the options listed above are not preferred.
When using essential oils remember to consider each person’s bio-individuality, age, health issues, and sensitivities. Less is always more with essential oils!

~ Less is always more with essential oils! ~
References:
1 Annmarie Skin Care, Ingredient watch list: Polysorbate 20-It may be contaminated with carcinogenic 1,4 dioxane, September 13, 2019
2 HealthTap
Resources:
Tisserand Institute, Bath Safety: how to use essential oils safely in the bath
Thank you, this is very good and very clear in your explanation.