A computer-based method for determining a sunscreen composition comprising a plurality of UV filter substances, comprising the steps of: a) selecting at least one constraint for at least one characteristic of the composition to be determined, the at least one constraint comprising a sunscreen performance target, the sunscreen performance target being chosen from one of the following: - in vivo or in vitro Sun Protection Factor SPF; - in vivo or in vitro UVA Protection Factor UVAPF; - critical wavelength; - ratio of UVA to UVB protection; and - blue light protection; b) selecting an optimization objective from a plurality of optimization objectives; c) automatically determining the sunscreen composition as a composition of filter substances from a set of filter substances, the sunscreen composition meeting the at least one constraint and being optimized with respect to the selected optimization objective, the automatic determination comprising the steps of: - generating a plurality of candidate compositions, - determining a sunscreen performance of the candidate compositions using a performance simulation tool and - comparing the determined sunscreen performance of the candidate compositions with the sunscreen performance target; wherein the automatic determination of the sunscreen composition comprises a numerical optimization of an objective function related to the selected optimization objective, the variables of the objective function including proportions of the filter substances of the sunscreen composition to be determined, using a numerical optimization algorithm which evaluates a first and a second derivative of the objective function for its choice of a search direction and step size taken at each iteration. a) selecting at least one constraint for at least one characteristic of the composition to be determined, the at least one constraint comprising a sunscreen performance target, the sunscreen performance target being chosen from one of the following: - in vivo or in vitro Sun Protection Factor SPF; - in vivo or in vitro UVA Protection Factor UVAPF; - critical wavelength; - ratio of UVA to UVB protection; and - blue light protection; - in vivo or in vitro Sun Protection Factor SPF; - in vivo or in vitro UVA Protection Factor UVAPF; - critical wavelength; - ratio of UVA to UVB protection; and - blue light protection; b) selecting an optimization objective from a plurality of optimization objectives; c) automatically determining the sunscreen composition as a composition of filter substances from a set of filter substances, the sunscreen composition meeting the at least one constraint and being optimized with respect to the selected optimization objective, the automatic determination comprising the steps of: - generating a plurality of candidate compositions, - determining a sunscreen performance of the candidate compositions using a performance simulation tool and - comparing the determined sunscreen performance of the candidate compositions with the sunscreen performance target; - generating a plurality of candidate compositions, - determining a sunscreen performance of the candidate compositions using a performance simulation tool and - comparing the determined sunscreen performance of the candidate compositions with the sunscreen performance target;