a nutrient in the vitamin b complex that the body needs in small amounts to function and stay healthy. bacteria that live in the intestines need para-aminobenzoic acid to survive. para-aminobenzoic acid is found in grains and foods from animals. it is being studied as a radiosensitizer (a substance that makes tumor cells more sensitive to radiation therapy) and in the treatment of certain skin disorders. also called aminobenzoic acid and paba.