Polyhydroxystearic Acid is a natural ingredient commonly used in sunscreens. It is a soft wax that is pliable and used most commonly as a coating on oxide particles that give sun protection. In our case it is a coating on the zinc oxide in our sunscreen. This is known as a dispersant.
Made from castor oil, Polyhydroxystearic Acid is a natural wax. The reason that oxide particles need a coating/dispersant is to allow them to properly disperse throughout the tube as they have a tendency to stick together. If they stick together, this means that not all portions of the sunscreen will have the same effectiveness for sun protection.
When a natural product like ours uses fatty acids and butters, like shea butter, a dispersant is needed in order to make the oxide particles spread out (they'd rather not). Since they are spread out it helps the oxide particles to significantly increase in their SPF and in turn UV absorption.