An aqueous composition, especially in the form of an aqueous solution or a hydrogel, comprising - a dihydrotriazine compound of the general formula I below: wherein - R 1 means (i) a phenyl group or a phenylalkyl group, each of which is optionally substituted with 1 to 3 substituents selected from the group consisting of C 1-6 -alkoxy group, hydroxy group, a halogen atom, C 1-6 -haloalkyl group, C 1-6 -alkyl group, a sulfonamido group and C 1-6 -haloalkoxy group, (ii) a naphthyl group or a naphthylalkyl group, (iii) a heterocyclic group, a heterocyclic alkyl group or a heterocyclic aminoalkyl group, (iv) an alkyl group having 1 to 16 carbon atoms or (v) a cycloalkyl group or a cycloalkylalkyl group, - R 1 ' means a hydrogen atom which is bonded to the nitrogen atom at position 1 or 3 of the dihydrotriazine ring, - R 2 and R 3 independently of one another mean a hydrogen atom or a methyl group, - R 4 means an alkyl group having 7 to 16 carbon atoms and - the dashed line indicates that the position of a double bond is either between positions 1 and 2 or between positions 2 and 3 of the dihydrotriazine ring, or a tautomer thereof or a salt thereof and - a defoamer for use in the prevention or treatment of infections and/or infectious diseases caused or partly caused by fungi. - a dihydrotriazine compound of the general formula I below: wherein - R 1 means (i) a phenyl group or a phenylalkyl group, each of which is optionally substituted with 1 to 3 substituents selected from the group consisting of C 1-6 -alkoxy group, hydroxy group, a halogen atom, C 1-6 -haloalkyl group, C 1-6 -alkyl group, a sulfonamido group and C 1-6 -haloalkoxy group, (ii) a naphthyl group or a naphthylalkyl group, (iii) a heterocyclic group, a heterocyclic alkyl group or a heterocyclic aminoalkyl group, (iv) an alkyl group having 1 to 16 carbon atoms or (v) a cycloalkyl group or a cycloalkylalkyl group, - R 1 ' means a hydrogen atom which is bonded to the nitrogen atom at position 1 or 3 of the dihydrotriazine ring, - R 2 and R 3 independently of one another mean a hydrogen atom or a methyl group, - R 4 means an alkyl group having 7 to 16 carbon atoms and - the dashed line indicates that the position of a double bond is either between positions 1 and 2 or between positions 2 and 3 of the dihydrotriazine ring, or a tautomer thereof or a salt thereof and - R 1 means (i) a phenyl group or a phenylalkyl group, each of which is optionally substituted with 1 to 3 substituents selected from the group consisting of C 1-6 -alkoxy group, hydroxy group, a halogen atom, C 1-6 -haloalkyl group, C 1-6 -alkyl group, a sulfonamido group and C 1-6 -haloalkoxy group, (ii) a naphthyl group or a naphthylalkyl group, (iii) a heterocyclic group, a heterocyclic alkyl group or a heterocyclic aminoalkyl group, (iv) an alkyl group having 1 to 16 carbon atoms or (v) a cycloalkyl group or a cycloalkylalkyl group, - R 1 ' means a hydrogen atom which is bonded to the nitrogen atom at position 1 or 3 of the dihydrotriazine ring, - R 2 and R 3 independently of one another mean a hydrogen atom or a methyl group, - R 4 means an alkyl group having 7 to 16 carbon atoms and - the dashed line indicates that the position of a double bond is either between positions 1 and 2 or between positions 2 and 3 of the dihydrotriazine ring, - a defoamer