Lye (sodium hydroxide) has a bad reputation in the Australian natural-beauty market, but here is the truth: without it, you do not have soap, you have a detergent blend. Lye reacts with oils and fats in a process called saponification, and once that reaction completes, no lye remains in the finished bar.
Saponification is a genuine chemical transformation, not a marketing term. Fats and oils are made of triglycerides; when sodium hydroxide is dissolved in water and mixed with those oils, it breaks each triglyceride apart into glycerine and fatty acid salts - which is what soap actually is. A well-formulated cold process recipe is calculated so that slightly more oil goes in than the lye can react with, leaving a small amount of unreacted, skin-conditioning oil (often called "superfat") in the cured bar, rather than any leftover lye.
Reputable Australian soap makers will list "sodium hydroxide" in the ingredients precisely because they have gone through this process correctly - the ACCC's guidance on cosmetic labelling expects accurate ingredient disclosure. Be more sceptical of a bar that markets itself as "lye-free," since true bar soap cannot exist without lye at some stage; what that claim usually means is the maker bought a pre-made "melt and pour" base where someone else already did the saponification.
What you actually want to check for on an Australian label is the finished pH (a well-cured bar sits around 9-10, which is normal for soap and not a sign of harshness on its own) and whether harsh synthetic fragrances or sulfates have been added on top of the base recipe. A four-to-six week cure time is also a good sign, since it gives the bar time to fully saponify and harden into a milder, longer-lasting product.
If you are buying from a small Australian soap maker at a farmers' market or online, it is reasonable to ask how long they cure their bars and what their superfat percentage is - a maker who can answer confidently is usually one who understands the chemistry rather than just following a kit recipe.
