Compounds of the formula I ##STR1## where the individual radicals R are identical or different and are each hydrogen, an alkali metal, or ammonium which is unsubstituted or substituted by organic radicals, or are each C.sub.1 -C.sub.20 -alkyl or a polyoxyethylene radical which contains from 1 to 10 ethylene oxide units and whose terminal OH group may be etherified by an alcohol of 1 to 3 carbon atoms, are used as sun screen agents.