I wish there was such a thing as a completely natural soap made only from coconut oil, olive oil, essential oils etc. But this is unfortunately impossible. There is absolutely no way to make a bar soap without using lye.
The basic reaction that is needed to make soap, called ‘saponification’, cannot occur without some form of lye reacting with some form of oil. Lye is actually a general term for a very strong alkali. There are two alkali’s that can be used to make soap: sodium hydroxide (caustic soda) and potassium hydroxide. Both are considered lye, but the potassium hydroxide is not strong enough to make a solid soap. It is only used for making liquid soaps.
Therefore sodium hydroxide cannot be substituted for potassium hydroxide and vice versa because soap making recipes will have different quantity requirements for these two chemicals depending on the kind of soap being manufactured. In addition, the quantities required for soap saponification differ when using caustic soda and hydrated potash.
Soap manufacturers do everything they can to hide the fact that they use lye in their soap. Dr. Bronners soap, which is considered “pure” natural, uses lye. It is hidden under the term “saponified oils”, which is actually the process of mixing lye with oil. Soap simply cannot be made without lye.
Lye is commercially manufactured using a membrane cell chlor-alkali process. It is one of the highest volume industrial chemicals with an annual production of 40 million tons. It is supplied in various forms such as flakes, pellets, microbeads, coarse powder or a solution. I use flakes to make soap – but would use any form available.
Interesting enough, Lye is also used for other things:
Food uses: Lye is used to cure types of food, such as: lutefisk; olives (making them less bitter); canned mandarin oranges; pretzels etc. It is also used as a tenderizer in the crust of baked Cantonese moon cakes, and in lye-water “zongzi” (glutenous rice dumplings wrapped in bamboo leaves); in chewy, southern Chinese noodles popular in Hong Kong and southern China; plus, in Japanese ramen noodles.
Household uses: Lye is also valued for its cleaning effects. It is commonly the major constituent in commercial and industrial oven cleaners and clogged drain openers, due to its grease-dissolving abilities. Lye decomposes greases via alkaline ester hydrolysis, yielding water soluble, easily removed (e.g., rinsed away) residual substances.
It does have hazardous reactions and has a potentially destructive effect on living tissues (e.g., skin, flesh, and the cornea). Solutions containing it can cause chemical burns, permanent injuries, scarring, and blindness—immediately upon contact. Lye may be harmful or even fatal if swallowed; ingestion can cause esophageal stricture. Moreover, solvation of dry solid lye is highly exothermic; the resulting heat may cause additional burns, or, ignite flammables. Therefore it is extremely important to use personal protective equipment including safety glasses, chemical-resistant gloves, and adequate ventilation when using lye to make soap (or clean your drain).
The reaction between sodium hydroxide and a few metals is also hazardous. Aluminium reacts with lye to produce hydrogen gases. Since hydrogen is flammable, mixing a large quantity of lye (e.g., sodium hydroxide) and aluminum in a closed container is dangerous – especially when the system is at a high temperature, which speeds up the reaction. In addition to aluminum, lye may also react with magnesium; galvanized zinc; tin; chromium; brass; and, bronze—producing hydrogen gas. Therefore I always use plastic containers and glass when I make soap.