An SPF booster is provided, comprising: a multistage polymeric particle having a core comprising polymerized units of a monoethylenically unsaturated carboxylic acid core monomer and a non-ionic ethylenically unsaturated core monomer; an inner shell comprising polymerized units of a non-ionic ethylenically unsaturated inner shell monomer; a monoethylenically unsaturated carboxylic acid inner shell monomer and an aliphatic inner shell monomer; an outer shell comprising polymerized units of a non-ionic ethylenically unsaturated outer shell monomer; an aliphatic outer shell monomer; a monoethylenically unsaturated non-carboxylic acid outer shell monomer and an ethylenically unsaturated surfactant outer shell monomer; wherein the core, when dry, contains a void; and wherein the multistage polymeric particle has an average particle size, when dry, of 50 to 1,000 nm.