I've often been asked the difference between the stuff I make and the stuff they sell in the stores. So, here's the difference.
Soap is a hydrolyzed salt - the result of the chemical union between a fatty acid (oil) and lye (sodium hydroxide). When it is done correctly, the lye is all gone, used up in the process of saponification, or the transition of the two ingredients into soap. That is what I do - it's called cold process. This is different from hot process, but we won't get into that yet. When your grandma or great-grandma made soap a hundred years ago, they used the cold process of making soap. Grandma didn't know about saponification values, and the careful measuring I do was not done back then. Old fashioned lye soaps were often too harsh, a result of too much lye and not enough fat.
Grocery store soaps (unless you can find the brand called Grandma's or Octagon Castile) are detergents. They use chemicals to make their soaps, and they also take the good stuff out of the soap. Handmade cold process soaps retain their glycerin, which is a humectant (draws water out of the air), which is much better for your skin. Detergent bars often use harsh chemicals, and to my nose, even harsher scents. I haven't used a commercial bar of soap in many moons, and a lot of the reason I started making my own soap is because I'm allergic to the chemicals in the grocery store detergent bars.
Now, that doesn't mean you can't be allergic to a bar of cold process soap. However, you are less likely to be, and any soaper worth her salt (ha ha ha) will be happy to work with you. I do offer an unscented soap bar in my shop - the only thing I added to it was some jojoba oil as a "superfat" (extra oil added after saponification has occurred) to make it more nourishing. Jojoba oil is the closest thing in nature to our skin's own sebum.
