Cosmetic composition containing an N-mercaptoalkylalkanediamide or one of its cosmetically acceptable salts as reducing agent

A cosmetic composition for the first step of an operation for permanent deformation of hair wherein disulphide bonds of keratin are reduced, the composition comprising at least one compound having the following formula (I):

• ##STR19## in which:
• A denotes the divalent radical --(CH.sub.2).sub.n --, n being an integer from 2 to 5, or the divalent radical --(CH.sub.2).sub.2 --O--(CH.sub.2).sub.2 --,
• B denotes a radical, said radical being:
• (a) the divalent radical --(CH.sub.2).sub.m --, m being an integer from 1 to 7,
• (b) the divalent radical ##STR20## in which one of the groups R.sub.1, R.sub.2 and R.sub.3 denotes a radical, said radical being a linear or branched alkyl radical containing from 1 to 4 carbon atoms, methoxymethyl, phenyl, benzyl, cyclohexyl or cyclopentyl, and the other two groups are a hydrogen atom, p, q and r being 0 or an integer from 1 to 4 and wherein 1.ltoreq.p+q+r.ltoreq.4, and further wherein the p, q, or r corresponding to that radical R.sub.1, R.sub.2 or R.sub.3 which is said radical and is not a hydrogen atom is an integer from 1 to 4,
• (c) the divalent radical ##STR21## in which R.sub.4 and R.sub.5 either, being identical or different, denote a linear or branched alkyl radical containing from 1 to 4 carbon atoms, or, together with the adjacent carbon atoms, form a cyclohexane or cyclohexene ring,
• (d) the divalent radical ##STR22## in which one of R.sub.6 and R.sub.7 denotes an --NH.sub.2 radical and the other denotes a hydrogen atom;
• t being equal to 0 or 1, or
• (e) the divalent radical ##STR23## in which R.sub.8 and R.sub.9 either, being identical or different, denote a hydrogen atom or a linear or branched alkyl radical containing from 1 to 4 carbon atoms or, together with the adjacent carbon atoms, form a benzene ring,
• R and R', which are identical or different, denote:
• either a hydrogen atom or a radical, said radical being a linear or branched alkyl radical containing from 1 to 4 carbon atoms or a linear or branched hydroxyalkyl radical containing from 1 to 5 carbon atoms,
• or R denotes a hydrogen atom and R' denotes an aminoalkyl radical --(CH.sub.2).sub.v --NR.sub.10 R.sub.11 in which v is an integer from 1 to 3 and R.sub.10 and R.sub.11, which are identical or different, denote a hydrogen atom or a linear or branched alkyl radical containing from 1 to 3 carbon atoms, R.sub.10 and R.sub.11 being incapable of simultaneously denoting a hydrogen atom,
• or an organic salt or an inorganic salt of said at least one compound of formula (I), and a cosmetically acceptable carrier, wherein said composition additionally contains at least one disulphide, the composition being self-neutralizing.