Ingredients of Soap
The cheaper and commoner soaps, including laundry soaps, usually contain considerable quantities of alkali, which gives them good cleansing qualities but makes them irritating to the skin. Soaps containing glycerin (glycerine soaps), while pleasant to use, usually contain an excess of free alkali, added to maintain their brilliancy- They therefore have a drying effect upon the skin of many people and an irritating effect upon others.
A “super-fatted” soap—one made usually by the addition of about one per cent, of lanolin, a preparation of wool fat that overcomes the effect of excessive free alkali and does not become rancid—will prevent these effects upon the skin in most cases. But, of course, much depends upon whether or not the soap is removed from the skin before drying. Super-fatted soaps are the least irritating of all; but there is no soap made that is not irritating to some extent, though those persons with tough, leathery skins may detect no irritation even from the cheapest and poorest qualities.
The useful property of soaps is that of attacking dirt, grease, and animal debris, partly because of their free alkali, rendering these substances soluble in water and, therefore, readily removable. But the free alkali is not necessary, as soap itself has the same property and in the best soaps it is present in very minute quantities.