Fluorescent whitening agent formulation

The present invention provides a liquid fluorescent whitening agent formulation which is a solution having a viscosity of 50 to 5000 mPas, preferably 100 to 3500 mPas, especially 100 to 1000 mPas and which comprises: a) 10-25%, preferably 15-20% by weight of an anionic fluorescent whitening agent, based on the total weight of the formulation; b) 15-35%, preferably 20-30% by weight of a polar solvent, based on the total weight of the formulation; and c) 45-75%, preferably 50-70% by weight, based on the total weight of the formulation, of a nonionic surfactant having the formula: in which m is 1, 2, 3 or 4 and, when m is 1, R is a C8-C18-alkyl residue or a C8-C18-alkylcarboxy residue; when m is 2, R is a C2-C4alkylene glycol residue from which the two hydroxy groups have been removed; when m is 3, R is the residue of trimethylolpropane from which the three hydroxy groups have been removed; and when m is 4, R is the residue of pentaerythritol residue from which the four hydroxy groups have been removed; R1 is hydrogen, methyl or ethyl; and n is a number ranging from 1 to 40.