Chemist reviews Dr Bronner’s Castile soap

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As a practising organic chemist this post will explore the effectiveness of Dr. Bronner’s Castile soap as well as the ingredients list.

I started using Dr. Bronner’s Castile soap to wash my body roughly one year ago; I was looking for something that would be a bit more ‘kinder’ to the skin than typical shop-bought shower gels. Something with fewer unnecessary ingredients. Also, something more effective, I find a lot of shower gels to be a bit ineffective. One year on and I don’t use anything else.

Oh, and in case you were wondering what Castile soap is…..

Castile soap originates from the Castile region of Spain and was traditionally made from olive oil. Today, Castile soap may contain a variety of vegetable oils such as coconut, castor, or hemp oils.

About Dr. Bronner’s Castile soap

Dr. Bronner’s Castile soap comes in various different scents: Almond, Cherry Blossom, Citrus, Eucalyptus, Fragrance Free, Green Tea, Lavender, Peppermint, Rose and Tea Tree.

I personally have only used lavender and peppermint. Eventually I will get around to trying more, but you really don’t need very much of this stuff, so it lasts a really long time. This is because their liquid soaps are three times more concentrated than most liquid soaps on the market. Thus, more soap per bottle and less waste in packaging materials.

Dr. Bronner’s Castile soap is a popular choice for many reasons, but below are some really good ones:


Dr. Bronner’s Pure-Castile Liquid Soaps are made with over 90% organic ingredients. They are in compliance with the USDA National Organic Program (NOP), the same program that certifies organic foods. They state that “Real organic personal care does not use synthetic preservatives that can irritate skin. Natural, unrefined oils and waxes are used as emollients and moisturizers, instead of hydrogenated oils and synthetic silicones. Traditional natural soaps are used in hand and body washes, instead of modern synthetic surfactants made in part from petrochemicals”. In addition, over 70% of their ingredients are certified fair trade, meaning ethical working conditions & fair prices.


“Dr. Bronner’s liquid soaps are fully biodegradable & use all-natural, vegan ingredients that pose no threat to the environment. Our products & ingredients are never tested on animals & are cruelty-free.” As I’ve spoke about in a previous blog post, always be wary of brands claiming to be ‘all-natural’ – do your own research. Although, in this case the overall picture looks pretty good. Later in this post, we will explore the soap’s ingredients in more detail.


“Our liquid soaps are made with plant-based ingredients you can pronounce—no synthetic preservatives, thickeners, or foaming agents—which is good for the environment & great for your skin!”. I link again my previous blog post: “Are ‘natural’ beauty products better?”. This post discusses whether synthetic or ‘natural’ ingredients are better (if at all). Long story short, you can’t say synthetic is always worse than ‘natural’. It’s typically a case by case basis on which we should judge which is better.


Dr. Bronner’s is diverting discarded plastic from landfills by using & increasing demand for recycled plastic bottles. This eliminates waste & has a positive environmental impact!

Ingredients list

Now time to look at the ingredients list a little closer. I am going to base this section on the lavender scent. Most of these scents have the same base but differ slightly in their essential oil content and other supplementary oils.

Lavender pure-Castile liquid soap Ingredient list

Aqua, Potassium Cocoate (Saponified Coconut Oil*‡), Potassium Palm Kernelate (Saponified Palm Kernel Oil*‡), Potassium Olivate (Saponified Olive Oil*‡), Glycerin*, Lavandula Hybrida (Lavandin) Oil*, Potassium Hempseedate (Saponified Hemp Oil*), Potassium Jojobate (Saponified Jojoba Oil*), Lavandula Angustifolia (Lavender) oil*, Citric Acid, Tocopherol (Vitamin E), Helianthus Annuus Seed Oil (Sunflower Oil), Geraniol♢, Limonene♢, Linalool♢

*Certified Organic Ingredients/ ‡Certified Fair Trade Ingredients ♢From Pure Essential Oils

We can break down these ingredients into several categories: surfactants, fragrances and other.

Surfactants: Potassium Cocoate (Saponified Coconut Oil*‡), Potassium Palm Kernelate (Saponified Palm Kernel Oil*‡), Potassium Olivate (Saponified Olive Oil*‡), Potassium Hempseedate (Saponified Hemp Oil*) and Potassium Jojobate (Saponified Jojoba Oil*)

Fragrances: Lavandula Hybrida (Lavandin) Oil*, Lavandula Angustifolia (Lavender) oil*, Geraniol♢, Limonene♢ and Linalool♢

Other: Citric acid, Vitamin E, glycerin and Helianthus Annuus Seed Oil (Sunflower Oil)


Surfactants are the compounds present in this Castile soap (or in shower gels, shampoos etc) that actually clean us! A surfactant is a compound which lowers the surface tension between substances. This helps in the emulsification and the washing away of oil and dirt.

The main difference between Castile soap such as this, and shower gel, is in their surfactants (plus all the extras shower gels often contain). The surfactants found in this Castile soap are different to those found in shower gel. Dr. Bronner’s Castile soap uses surfactants generated by one of the oldest, most simple chemical reactions known: Saponification.

Here, the hydrolysis of a triglyceride (of which coconut, palm kernel, hemp and olive oils are sources. Triglyceride content in Jojoba oil is low but it can still undergo saponification) occurs using an aqueous alkali. The alkali used is potassium hydroxide when making Dr. Bronner’s Castile soap. This yields glycerol and 3 fatty acid salts (the surfactant/soap). A great thing about their coconut, palm kernel, hemp, olive and jojoba oils is that they are certified organic ingredients.

You may have noticed in their ingredients that they have listed glycerin*. You may also have noticed in my schematic above, that saponification generates a compound known as glycerol. Did I spell that wrong? Well no.

The true name for the compound generated from saponification is glycerol. Whereas, glycerine is actually the commercial name of glycerol, when it is not pure. Glycerin contains approximately 95% of glycerol.

Typically, commercial soap-makers distill the glycerin out of their soaps to sell separately. Whereas Dr. Bronner’s keep it in their soaps for its moisturising qualities.


The fragrances used in Dr. Bronner’s Castile soaps vary from scent to scent, but in the lavender scent we have: Lavandula Hybrida (Lavandin) Oil*, Lavandula Angustifolia (Lavender) oil*, Geraniol♢, Limonene♢ and Linalool♢.

The two Certified Organic oils Lavandula Hybrida (Lavandin) Oil* and Lavandula Angustifolia (Lavender) oil* are essentially different varieties of lavender that produce essential oil and are used to fragrance this soap.

The final compounds used for fragrance are: Geraniol♢, Limonene♢ and Linalool♢. So how do they differ to the lavender oils above? Lavandula Hybrida (Lavandin) Oil* and Lavandula Angustifolia (Lavender) oil* are 100% pure essential oils that were extracted from lavender. However, the diamond next to geraniol, limonene and linalool indicates that these compounds are from pure essential oils. Essential oils often contain multiple components. Geraniol, limonene and linalool were once one of these components.


Firstly, Dr. Bronner’s Castile soap contains citric acid. Citric acid occurs naturally in citrus fruits and it is one of the most common food additives in the world. Adding citric acid to the soap generates potassium citrate, which helps the soaps lathering ability and helps prevent soap scum.

Secondly, we have Vitamin E, a vitamin known for its moisturising effects. However, Dr. Bronner uses Vitamin E for ‘freshness’. Vitamin E is a known antioxidant and in theory it should stop the oxidation of oils. Many lotions, soaps and skincare products use Vitamin E to lengthen their shelf-life. Although, some studies have shown Vitamin E in soap does not work any better to prevent oxidation than no additive at all. At the very least, we have a decent moisturiser thrown in.

Lastly, I have already mentioned the hydrating effects of glycerol/glycerin, but we also have the added benefit of Helianthus Annuus Seed Oil (Sunflower Oil) in this formulation, which is considered an emollient (emollients cover the skin with a protective film to trap in moisture).

How to use Dr. Bronner’s Castile soap

Since it is a very concentrated soap it can be very drying (I personally don’t find it to be an issue, but others might). I find it to be much more effective than typical shower gels since these use synthetic surfactants, which in my personal experience don’t live up to traditional soap (which use surfactants derived from saponification), in terms of performance. But, if you find the Castile soap to be too drying then make sure to dilute it (or perhaps shower gel is more your thing, they tend to be less drying). I usually use a couple of drops per body part in the shower – the water in the shower dilutes the soap mixture – to dilute further perhaps just use a singular drop. For some people, however, it just won’t be suitable. Hopefully that won’t be the case because I find this product to be a lifesaver.

Dr. Bronner’s Castile soap actually has many other uses:

  1. Face: Wet face or hands with water and use as many drops as desired to wash the face.
  2. Hair: Work the soap into wet hair until it lathers. Then, wash and rinse.
  3. Shave: Use as a lubricant for shaving.
  4. Bath: Add 2 tablespoons to your bath. I think this would be particularly enjoyable using the lavender scent (I haven’t tried it yet).
  5. Toothpaste: The company suggest to use 1 drop on a toothbrush. Not sure I fancy that, but be my guest.
  6. Cleaning: This soap also works well as a household cleanser!

Key takeaways

  • Much more effective than typical shower gels bought in the supermarket
  • Practicality of being in a bottle just like shower gel
  • Fewer ingredients/kinder ingredients
  • Lasts a really long time
  • Has many other uses than just body wash