Lye (sodium hydroxide) has a bad reputation in the UK 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. Reputable UK soap makers will list "sodium hydroxide" in the ingredients precisely because they have gone through this process correctly. What you actually want to check for on a UK label is the finished pH (a well-cured bar sits around 9-10) and whether harsh synthetic fragrances or sulfates have been added on top of the base recipe.