Rosemary Leaf Extract, also known as rosemary oleoresin or ROE, is not a preservative. It is a very effective antioxidant. Preservatives inhibit the growth of mold, bacteria, yeast, fungus etc. in water-based products like lotions. Antioxidants slow down the oxidation of the oils. It's the oxidation of the oils that causes rancidity. When added to fresh oils, ROE can greatly extend the shelf life of the oils, especially of more fragile oils like hemp, avocado and grape seed.