4-Aminobenzoic acid (also known as para-aminobenzoic acid or PABA) is an organic compound with the molecular formula C7H7NO2. PABA is a white crystalline substance that is only slightly soluble in water. PABA is an essential nutrient for some microorganisms and is sometimes called Vitamin Bx. The most well-known property of PABA is as an effective sunscreen, when used topically. CAS No. 150-13-0 Sold per pound. Packaged in plastic bags or plastic containers depending on the quantity. Free shipping option available on orders of 5-lb and more.