Seventeen commercially available sunscreens were tested to determine their relative protection at 305 nm of monochromatic radiation. Tests, using 23 volunteers, were also made with four representative sunscreens: P-aminobenzoic acid (PABA) in alcoholic solution (Presun), cinoxate and menthyl anthranilate (Maxafil), the benzophenone mixture of oxybenzone and dioxybenzone (Solbar), and an ester of PABA (Pabafilm) were tested in the sunburn range at 295, 300, 305, and 313 nm. Alcoholic solutions of PABA were the most effective, with a mean protection factor (PF) of 17.6; esters of PABA were less effective, with a mean PF that ranged from 5.5 to 8.3, and were comparable to the benzophenones. A combination of cinoxate and menthyl anthranilate (Maxafil) gave a mean PF of 9.6. There was no significant difference in the PF with the different wavelengths 295 to 313 nm.
Cripps DJ, Hegedus S. Protection Factor of Sunscreens to Monochromatic Radiation. Arch Dermatol. 1974;109(2):202-204. doi:10.1001/archderm.1974.01630020018003