A hair shampoo comprises 0,05 to 20% of a water-soluble skin-compatible reducing agent and 0,05 to 10% of a diamide having the formula:-  <FORM:0908888/III/1> or <FORM:0908888/III/2> wherein X1 and X2 may be the same or different and represent O or S, and R1, R2, R3, R4 and R5 may be the same or different and represent hydrogen, alkyl, alkylol or acyl groups.  The ratio of reducing agent to diamide is from 1:5 to 5:1.  Specified reducing agents are water-soluble salts of sulphur oxygen acids having two or three sulphur atoms, e.g. salts of dithionous acid, thiosulphuric acid and trithionic acid particularly the sodium and potassium salts, and reducing sugars such as glucose, fructose, invert sugar, maltose, lactose and galactose.  The diamides include urea, thiourea, buiret, thiobuiret, dithiobuiret and their water-soluble or alcohol soluble mono- and poly-alkyl alkylol and acyl derivatives.  The alkyl, alkylol and acyl groups may be saturated or unsaturated, straight or branched chain and should not contain more than four carbon atoms. In the case of buiret derivatives it is preferred that the chain length of the groups should not exceed two carbon atoms.  The shampoo may be liquid, e.g. an aqueous or alcoholic solution, paste or solid and contains conventional soaps or synthetic detergents, for example, alkyd sulphates and phosphates, fatty acyl mono-glyceride sulphates, fatty esters of hydroxyalkane sulphonates, alkanolamide sulphates, N-fatty acyl taurides, alkylaryl sulphonates, sulphated ethylene oxide condensates with fatty acids and alcohols and with alkylaryl radicals, and sulphonated oils, all of which may be present as the alkali metal, ammonium, or lower alkanolamine salts; ethylene oxide condensates with fatty acids and alcohols, alkylaryl radicals, polypropylene glycols or alkanolamides, or fatty acyl lysalbinates; N-acyl pyridinium halides or tetraalkylammonium halides, or the acetates or sulphates thereof; N-alkyl-b -aminopropionic acid.  The detergent preferably comprises 5-40% of a liquid or paste composition and 15 to 98% of a solid or powder composition.  The shampoo may also include castor or mineral oil, polyhydric alcohol, polyalkylene glycol ethers, fatty acid esters of alcohols or polyglycol ethers, gum tragacanth and shellac.  The pH is preferably 4 to 10 but in soap containing hair preparations it is above 8.  Optional additions are vitamins, hormones, lanolin, bactericides, plant extracts and buffers.  Specification 907,188 is referred to.ALSO:A hair preparation comprises 0.05 to 20% of a water-soluble skin-compatible reducing agent and 0.05 to 10% of a diamide having the formula <FORM:0908888/VI/1> wherein X1 and X2 may be the same or different and represent O or S, and R1, R2, R3, R4 and R5 may be the same or different and represent hydrogen, alkyl, alkylol or acyl groups.  The ratio of reducing agent to diamide is from 1 : 5 to 5 : 1.  Specified reducing agents are water-soluble salts of sulphur oxygen acids having two or three sulphur atoms, e.g. salts of dithionous acid, thiosulphuric acid and trithionic acid particularly the sodium and potassium salts, and reducing sugars such as glucose, fructose, invert sugar, maltose, lactose and galactose.  The diamides include urea, thiourea, biuret, thiobiuret, dithiobiuret and their water-soluble or alcohol soluble mono- and polyalkyl alkylol and acyl derivatives.  The alkyl, alkylol and acyl groups may be saturated or unsaturated, straight or branched chain and should not contain more than four carbon atoms.  In the case of biuret derivatives it is preferred that the chain length of the groups should not exceed two carbon atoms.  The hair tonic or dressing may take the form of an aqueous, alcoholic or aqueous alcoholic solution.  An optional ingredient is a non-volatile organic compound which facilitates hair grooming, e.g. castor oil, mineral oil, glycerol, gums and lacquers such as shellac.  The pH is preferably 4 to 10 but in soap containing hair preparations it is above 8.  Optional additions are vitamins, hormones, lanolin, bactericides, plant extracts and buffers. Specification 907,188 is referred to.