The sunscreening efficacy of aminobenzoic acid and two of its best known esters was appraised on human subjects using solar-simulating radiation from the xenon lamp. Protection was measured in terms of the protective index, the ratio of the highest nonerythemogenic dose on the treated area to the minimal erythemal dose determined on a nearby untreated site.
Willis I, Kligman AM. Aminobenzoic Acid and Its EstersThe Quest for More Effective Sunscreens. Arch Dermatol. 1970;102(4):405-417. doi:10.1001/archderm.1970.04000100053012