The naturally-occurring glycerin, a moisturizer, is also removed from commercial soaps (so the bars are harder and longer-lasting). This is why we can't wash our faces with commercial soap, and instead need to now buy an additional product (presumably offered by the same company) to wash our faces.
Another danger of store-bought soap is that animal testing is still being used. Commercial soaps that test on animals include: Camay, Ivory, Oil of Olay, and Zest. Possibly even more disturbing is that many namebrand soaps are made with animal by-products (tallow, lard). Not only are these by-products full of toxic growth hormones, but they clog pores. Commercial soaps made with animal by-products: Irish Spring, Dove, Camay, Dial, and Lever 2000.
According to KitchenDoctor.Com, commercial soaps are "laced with antibiotics and derivatives of the petrochemical industry that eventually end up in our sewage and septic systems." So, be sure to factory in the harms of factory pollution, corporate waste, multi-national conglomerate corporations, globalization, and over-all corporate control in your new passion for handmade soapmaking.
According to FDA/CFSAN.Gov, "Today, there are very few true soaps in the traditional sense on the market...Most body cleansers on the market today are actually synthetic detergent products..." This is why you'll see things in the soap aisle labeled "beauty bars," "deodorant bars," and "antibacterial bars." These chemical mutations masquerading as soap no longer meet the FDA's definition of soap, which is pretty hard to do.
And, speaking of the FDA, they do not require the ingredients of true soaps to be disclosed to consumers. To this day, nobody knows what's in Jergen's or Ivory.