Stearic Acid is a commonly used, safe fatty acid found in things like shea butter and coconut oil. It is used for creating more moisture in products, and create a softer texture. We have tested it out, but never pulled through to production on formulas that use stearic acid.
Do not use stearic acid on its own, as it can cause irritation. Use only 2-5% of it in your formula. Click HERE for a great introduction to using Stearic Acid in DIY homemade products: