PABA is an essential nutrient for some bacteria and is sometimes called Vitamin Bx[1]. In humans, PABA is normally made by E-coli[2] in the colon and therefore PABA from food is not normally essential to human health. PABA is therefore not officially classified as a vitamin. PABA is an intermediate in bacterial synthesis of folate. Although humans lack the ability to synthesize folate from PABA, that is also normally done by E-coli.[3] PABA is sometimes marketed as an essential nutrient for use whenever normal PABA synthesis by intestinal bacteria is insufficient. Symptoms of PABA deficiency may include scleroderma (hardening of skin), weeping eczema (moist eczema), skin infections, and patchy pigment loss in skin (vitiligo).[4] Food sources of PABA include liver, brewer's yeast (and unfiltered beer), kidney, molasses, and whole grains. Sulfonamides are chemically similar to PABA, and their antibacterial activity is due to their ability to interfere with conversion of PABA to folate by dihydropteroate synthetase, and subsequent utilization, by bacteria.