The invention thus relates to the cosmetic use of a siliceous material that may be obtained by hydrolysis and condensation, in the presence of water, of at least one tetraalkoxysilane of formula (I) below: Si(OR2)4 (I) and of an alkyltrialkoxysilane of formula (II) below: R1Si(OR2)3 (H) in which: R1 denotes a C7 to C20 alkyl group, optionally interrupted in its chain with an O or S atom or with an NH group or a carbonyl group (CO), R2 denotes a C1-C4 alkyl group. Preferentially, the siliceous material is present in a composition comprising a cosmetically acceptable medium. The invention also relates to a cosmetic process for treating human body odour, in particular underarm odour and optionally human perspiration, which consists in applying to human keratin materials the said siliceous material or a composition containing the same in a cosmetically acceptable medium. The invention also relates to a composition characterized in that it comprises, in a cosmetically acceptable medium, at least the said siliceous material and at least one deodorant agent other than the said siliceous material and/or at least one antiperspirant active agent.