GB2187197A - Antidandruff shampoo compositions - Google Patents

Abstract

Antidandruff shampoo compositions comprise 5% to 50% surfactant, 0.1% to 5% of water-insoluble antidandruff agent (a 1-hydroxy-2-pyridinethione salt), and from 0:1% to 15% by weight of a diffusion promoter which is a water-soluble salt of cumene sulfonic acid. The compositions provide improved antidandruff efficacy together with excellent storage stability and special viscosity characteristics.

Description

SPECIFICATION Shampoo compositions Technical field The present invention relates to antidandruff shampoo compositions. In particular it relates to shampoo compositions having improved antidandruff efficacy aswell as excellent storage stability and viscosity control.

Background Dandruff is a widespread probiem, some 50%-60% ofthe overall population suffering with dandruff at varying periods oftheir lives and to varying degrees. Although the cause or cause of dandruff are still not precisely settled, the microorganism Pityrosporum Ovale is strongly implicated in the etiology ofthe scruf-formation process.

The use of pyridinethione salts as antidandruffagents in shampoos and hair rinse is well known.

US-A-3,236,733 discloses detergent compositions containing such salts. Other references include US-A-2,809,971 and US-A-3,723,325.

The pyridinethione salts have been clinically proven to reduce the level of dandruffwhen used regularly over, for example, a fourweek period. Typically, there is a reduction in mean dandruff grades of about 50%-70% afterfourweeks twice weekly usage. Continued treatment can provide some further marginal improvements but on average, these materials reach a plateau in anti-dandruff effectiveness. Improvements in the level of dandruff reduction or in the rate of which dandruff reduction is achieved or in the weigh effectiveness of the antidandruff agent, would therefore be highly desirable.

Some improvement in antidandruff activity can be achieved through the addition of strong electrolytes such as sodium chloride and these adjuncts are also known to be effective in modifying product viscosity.

Unfortunately, strong electrolytes tend to have an adverse effect on the long term product stability of liquid shampoo compositions, especially in the case of compositions based on ammonium alkyl sulfates and ethoxylated alkyl sulfates as the principal detergent component. Where, on the other hand, conventional hydrotopes such as ammonium xylene sulfonate are used for viscosity control, these are found to interfere with antidandruff performance, particularly in the case of those users having relatively severe dandruff problems or who shampoo their hair infrequently.

Accordingly, the present invention provides antidandruff shampoo compositions having improved antidandruff efficacytogetherwith excellent formulation stability and viscosity characteristics as well as desirable dispensing, lathering and in-use shampooing properties and product appearance.

Summaryof the invention According to a first aspect of the invention, there is provided an antidandruff shampoo composition comprising: (a) from about 5% to about 50% by weight of surfactant selected from anionic, nonionic, amphoteric, zwitterionic and cationic surfactants and mixturesthereof, (b) from about 0.1% to about 5% by weight of a water-insoluble salt of 1-hydroxy-2-pyridinethione (I), and (c) from about 0.1% to about 15% by weight of a diffusion promoter selected from the water-soluble salts of cumene sulfonic acid.

The antidandruff component preferred for use herein is a water-insoluble pyridinethione. The pyrinethione can generally be defined as water-insoluble salts of 1 -hydroxy-2-pyridinethione which has thefollowing structural formula in tautomeric form, the sulfur being attached to the No. 2 position in the pyridine ring.

The salts resultfrom substitution ofthe hydrogen of one ofthetautomericforms by the appropriate salt cation. Depending, of course, on the valence of the salt cation involved there may be more than one ofthe pyridinethione rings in the compound.

Preferred salts are formed from heavy metals such as zinc, tin, cadmium, magnesium, aluminium and zirconium. The preferred heavy metal is zinc. Other cations such as sodium are also suitable, however.

The pyridinethiones generally take the form ofwater-insoluble particles. These can have an individual particle size of at least 1 micrometer. Preferred materials, however, are pyridinethione crystals in the form of predominantly flat platelets which have a mean sphericity of lessthan about 0.65, preferably from about 0.20 to about 0.54 and a median particle size of at least about 2 micrometers, the particle size being expressed as the median equivalent diameter of a sphere of equal volume. The upper limit on mean particle size is not critical but generally can range up to about 25 micrometers, measured on the same basis. The median diameters are on a mass basis with 50% ofthe mass of particles faliing on either side of the value given.

The diameter of a sphere of equivalentvolumefora particle can be determined by a varietyof sedimentation techniques which are based on Stokes' Law for the settling velocity of a particle in a fluid. Such techniques are described in Stockham, J.D. and Fochtman, E.G., Particle SizeAnalysis, Ann Arbor Science, 1978. An approach for determining the median equivalentAnalysis,Ann Arbor Science, 1978. An approach for determining the median equivalent spherical diameter based on volume, is shown in EP-A-34,385, Example II.

The sphericity of a particle is also described by Stockham and Fochtman at page 113 as (dud,)2, where dv is the diameter of a sphere of equivalentvolume, supra, and d3 is the diameter of a sphere of equivalent area. As used herein, however, the mean sphericity is (Wv/ds)2, orthe surface area of spheres having equivalent volume distribution divided by the actual surface area of particles as measured. Atechniquefor determining actual surface area is shown in the examples using the BETtechnique described by Stockham and Fochtman at page 122.

From the viewpoint ofanti-dandruff efficacy, the BET surface area herein preferably falls in the range from about 0.5 to about 3.5, more preferably from about 1.0 to about 3.0 m2/g.

In preferred embodiments, pyridonethione anti-dandruff agents herein are at least partly in agglomerated form, the agglomerate size preferably being such that at least about 20% by weight, more preferably at least about 50% by weight ofthe pyridonethione is in the form of agglomerates having an equivalentspherical diameter of at least about 5 microns, preferably from about 7 to about 30 microns, more preferablyfrom about 1 to about 20 microns. Agglomerate size is conveniently measured by sedimentation techniques using a Sedigraph 5000, Micrometrics Corp., the agglomerates being predispersed in water under low shear conditions. Agglomeration is preferred from the viewpoint of optimizing overall formulation anti-dandruff efficacy.

The water-insoluble antidandruff agent is present generally at a level offrom about 0.1% to about5%, preferably from about 0.1% to about 3%, more preferably from about 0.2% to about 2% by weight of composition.

Afurther essential component ofthe antidandruff shampoo compositions is a surfactant. The term surfactant" as used herein is intended to denote soap and nonsoap surfactants. The surfactant component usually comprises from about 5%to about 50% by weight of the composition, preferably from about 1 0%to about 20%.

Any nonsoap surfactant is suitable for use including anionic, nonionic, amphoteric, zwitterionic and cationic types.

Examples of suitable soaps arethe sodium, potassium, ammonium and alkanol ammonium salts of higher fatty acids (those having 10-20 carbon atoms). Anionic nonsoap surfactants can be exemplified by the alkali metal salts of organic sulfuric reaction products having in their molecular structure an alkyl radical containing from 8 - 22 carbon atoms and a sulfonic acid or sulfuric acid ester radical (included in the term alkyl is the alkyl portion of higheracyl radicals).Preferred are the sodium, ammonium, potassium or triethanolamine alkyl sulfates, especiallythose obtained by sulfating the higher alcohols (C8 - Cite carbon atoms), sodium coconut oil fatty acid monoglyceridesulfates and sulfonates; sodium or potassium salts of sulfuric acid esters of the reaction product of 1 mole of a higher fatty alcohol (e.g., tallow or coconutoil alcohols) and 1 to 12 moles of ethylene oxide; sodium or potassium salts of alkyl phenol ethylene oxide ether sulfate with 1 to 10 units of ethylene oxide per molecule and in which the alkyl radicals contain from 8 to 12 carbon atoms, sodium alkyl glyceryl ether sulfonates; the reaction product of fatty acids having from 10 to 22 carbon atoms esterified with isethionic acid and neutralized with sodium hydroxide; water soluble salts of condensation products of fatty acids with sarcosine; and other known in the art.

Of the above, anionic surfactants preferred herein are alkyl sulphates, ethoxylated alkyl sulphates and mixtures thereof. Highly preferred herein are ammonium alkyl sulphates, ammonium ethoxylated alkyl sulphates and mixtures thereof.

Nonionic surfactants can be broadly defined as compounds produced bythe condensation ofalkylene oxide groups (hydrophilic in nature) with an organic hydrophobic compound,which may be aliphatic or alkyl aromatic in nature. Examples of preferred classes of nonionic surfactants are: 1. The polyethylene oxide condensates of alkyl phenols, e.g., the condensation products of alkyl phenols having an alkyl group containing from about6 to 12 carbon atoms in either a straight chain or branched chain configuration, with ethylene oxide, the said ethylene oxide being present in amounts equal to 10 to 60 moles of ethylene oxide per mole of alkyl phenol.The alkyl substituent in such compounds may be derived from polymeri,:ed propyiene, diisobutyiene, octane, or nonane, for example.

2. Those derived from the condensation of ethylene oxide with the product resulting from the reaction of propylene oxide and ethylene diamine products which may be varied in composition depending upon the balance between the hydrophobic and hydrophilic elements which is desired. For example, compounds containing from about 40% to about 80% polyoxyethylene by weight and having a molecularweight offrom about 5,000 to about 11,000 resulting from the reaction ofethylene oxide g rou ps with a hydrophobic base constituted of the reaction product of ethylene diamine and excess propylene oxide, said base having a molecularweight of the order of 2,500 to 3,000, are satisfactory.

3. The condensation product of aliphatic alcohols having from 8to 18 carbon atoms, in either straight chain or branched chain configuration,with ethylene oxide, e.g., a coconutalcohol ethylene oxide condensate having from 10 to 30 moles of ethylene oxide per mole of coconut alcohol, the coconut alcohol fraction having from 10 to 14 carbon atoms.

4. Long chain tertiary amine oxides corresponding tothefollowing general formula: R1R2R3N + O wherein R1 contains an alkyl, alkenyl ormonohydroxy alkyl radical offrom about8to about 18 carbon atoms, from O to about 10 ethylene oxide moieties, and from O to 1 glyceryl moiety, and R2 and R3 contain from 1 to about 3 carbon atoms and from 0 to about 1 hydroxy group, e.g., methyl, ethyl, propyl, hydroxy ethyl, or hydroxy propyl radicals. The arrow in the formula is a conventional representation of a semipolar bond.

Examples of amine oxides suitable for use in this invention include dimethyldodecylamine oxide, oleyldi(2-hydroxyethyl)amine oxide, dimethyloctylamine oxide, dimethyldecylamine oxide, dimethyltetradecylamine oxide, 3,6,9-trioxaheptadecyldiethylamine oxide, di(2-hydroxyethyl)-tetradecylamine oxide, 2-dodecoxyethyldimethylami ne oxide, 3-dodeoxycy-2-hydroxypropyldi(3-hydroxypropyl)amine oxide, dimethylhexadecylamine oxide.

Zwitterionic surfactants can be exemplified by those which can be broadly described as derivatives of aliphatic quaternary ammonium, phosphonium, and sulfonium compounds, in which the aliphatic radicals can be straight chain or branched, and wherein one of the aliphatic substituents contains from about 8 to 18 carbon atoms and one contains an anionicwater-solubilizing group, e.g., carboxy, sulfonate, sulfate, phosphate, or phosphonate.A general formula for these compounds is:

wherein R2 contains an alkyl, alkenyl, or hydroxy alkyl radical of from about 8to about 18 carbon atoms, from Oto aboutl0 ethylene oxide moieties and from Oto 1 glyceryl moiety; Y is selected from nitrogen, phosphorus, and sulfur atoms, R3 is an alkyl or monohydroxyalkyl group containing 1 to about3 carbon atoms; xis 1 when Y is a sulfur atom and 2 when Y is a nitrogen or phosphorus atom; R4 is an alkylene or hydroxyalkylene offrom 1 to about 4 carbon atoms and Z is a radical selected from carboxylate,sulfonate, sulfate, phosphonate, and phosphate groups.

Examples of amphoteric surfactants which can be used in the compositions of the present invention can be broadly described as derivatives of aliphatic secondary and tertiary amines in which the aliphatic radical can be straight chain or branched and wherein one of the aliphatic substituents contains from about 8 to about 18 carbon atoms and one contains an anionic water solubilizing group, e.g., carboxy, sulfonate, sulfate, phosphate, or phosponate.Examples of compounds falling within this definition are sodium 3-dodecylaminopropionate, sodium 3-dodecylaminopropane sulfonate, N-alkyltaurines such as the one prepared by reacting dodecylaminewith sodium isethionate according to the teaching of US-A-2,658,072, N-higher alkyl aspartic acids such as those produced according to the teaching of US-A-2,438,091,and the products sold underthe trade name "Miranol" and described in US-A-2,528,378.

Many cationic surfactants are known to the art. Byway of example, the following may be mentioned: dodecyltrimethylammonium chloride; nonylbenzylethyldimethylammonium nitrate; tetradecylpyridinium bromide; laurylpyridinium chloride; cetylpyridinium chloride; laurylpyridinium chloride; laurylisoquinolium bromide; ditallow(hydrogenated)dimethyl ammonium chloride dilauryldimethylammonium chloride; and stearalkonium chloride.

Many additional nonsoap surfactants are described in McCUTCHEON'S, DETERGENTS AND EMULSIFIERS, 1979ANNUAL, published by Allured Publishing Corporation.

The above-mentioned surfactants can be used alone or in combination in the shampoo compositions of the present invention.

Another essential component of the compositions of the invention is a diffusion promoter. The effect ofthe promoter is to enhance the antidandruff efficacy of the composition whilst maintaining good viscosity and stability characteristics. Preferred promoters for use herein are the water-soluble salts of cumene sulfonic acid, highly preferred being sodium cumene sulfonate. Whilst not wishing to be bound by theory, it is believed that the promoter acts by modifying the phase/micelle structure of the shampoo composition which in turn effects both composition rheology and the rate of diffusion ofthe antidandruff agent from the shampoo base onto the scalp.In rheological terms, the compositions herein preferably take theform of a shear thinning liquid, the viscosity of which is at least 1500 cP, preferably at least 2000 cP, more preferably at least 2500 cP at4sec-' and which is at least 500 cP, preferably at least 1000 cP lowerat40sec-1,viscosity being measured herein at 20"C (68 F) using a Haake RV12 with MVII torque sensor.Suitable diffusion promoters herein can also be selected on the basis of their effect in enhancing the "diffusion concentration" of antidandruffagent, i.e., the concentration ofantidandruffagentwhich diffuses through a Spectropore semipermeable cellulose membrane supplied by Pearce and Warriner, Cheshire, UK, Catalog No.132634 (1000 m.wt cut-off) from 6g of a shampoo base having a 1% by weight antidandruff active concentration into 50ml of water at 100 F (37.8"C) without agitation over a period of 60 minutes, preferred materials herein providing at least a 50% increase in diffusion concentration and highly preferred materials providing at least a 100% increase in diffusion concentration.In absolute terms, the diffusion concentration of the composition underthe above test conditions is preferably at least about 4ppm, more preferably at least about 7ppm, and most preferablyfrom about 8ppm to 20ppm. A suitable method for measuring diffusion concentration is by atomic absorption analysis.

The diffusion promoter is generally added at a level in the range from about 0.1 %to about 15%, preferably from about 0.2% to 10%, and especialiyfrom about0.5%to about 5% byweight of composition.

In a second aspect of the invention, there is provided an antidandruff shampoo composition comprising: (a) from 5% to 50% by weight ofsurfactant selected from anionic, nonionic, amphoteric and zwitterionic surfactants and mixtures thereof, (b) from 0.1% to 5% by weight of a water-insoluble anti-dandruff agent, and (c) from 0.1% to 15% of a diffusion promoter therefor, the composition having a Haake viscosity at20"C and 4sec- of at least 1500 cP, preferably at least 2000 cP and more preferably at least 2500 cP and a Haake viscosity at 20"C and 40 sec-l which is at least 500 cP, preferably at least 1000 cP less than the 4sec-1 value.

The shampoo compositions can be complemented by a variety of non-essential ingredients in their well-known art-established functionality.

Thus, the shampoo compositions herein can additionally contain a water-soluble orsolubilization antidandruff agent such as a hydroxypyridone having the general formula II, or a saltthereof

wherein R is an aliphatic or aromatic moiety having a factor of at least about 1.3, The hydroxypyridone component (II) can generally be described as 1-hydroxy-4-methyl-(1 H)-pyridones having an aliphatic or aromatic moiety (R) at the 6 position thereof, wherein R has a factor of at least 1.3, preferably from 2 to 6, more preferably from 3to 5.5. The factor is a measure of the lipophilicity/hydrophilicity ofthe substituent and is defined in detain in the paper byW. Dittmar, E. Druckrey and H. Urbach,J. Med.

Chem. 17(7), 753-6(1974) and reference cited therein.

In structural terms, preferred R substituents are selected from linear and branched C3.Cllr preferably C6-C11 alkyl and alkenyl groups, C5-C8 cycloaikyl groups, and aryl groups. In the above, cyclic moieties can also be substituted with one or more alkyl or alkenyl groups upto C4. The R groups can further be substituted with halogen atoms. Of the above, preferred R moieties are cyclohexyl and 2,4,4-trimethyl pentyl,the latter being highly preferred.

The above mentioned compounds can be used both in the free form and as salts, for example, salts with organic bases or inorganic cations. Low molecular weight alkanolamines are especially preferred organic bases, for example triethanoiam ine.

The shampoo composition will generally contain a suspending agent. The suspending agent is preferably substantially crystalline in form. Also, preferred suspending agents are non-polymeric and non-clay in nature, such materials being found to have a deleterious effect on overall anti-dandruff efficacy. Accordingly, the shampoo compositions are preferably substantiallyfree of nonionic and anionic polymeric and clay-type suspending agents. By "substantially free" it is meant not more than about 20 ppm ofthese materials.

Preferred suspending agents include ethylene glycol and glycerol esters of fatty acids having from about 16 to about 22 carbon atoms. Both ethylene glycol mono and distearate are examples ofthese esters.

Other useful suspending agents are alkanolamides offatty acids having from about 16 to about 22 carbon atoms, preferably about 16 to 18 carbon atoms. Suitable examples ofthese agents include stearic monoethanolamide, stearic diethanolamide, stearic monoisopropanolamide, stearic diethanolamide distearate and mixtures thereof.

Still other suitable suspending agents are C16-C22 alkyl dimethylamine oxides such as stearyl dimethyl amine oxide and C16-C22 fatty acid amidoalkylamines such as stearamidoethyldiethylamine. Mixtures of suspending agents are also acceptable, for example, a mixture of g lyceryl stearate and stearamidoethyldiethylamine. When present, these suspending agents are at levels of from about 1% to about7%, preferably from about 2% to about 6%. These agents may also serve to give pearlescence to the product.

The shampoo composition can contain a variety of non-essential optional ingredients suitable for rendering such compositions more desirable. Such conventional optional ingredients are well knownto those skilled in the art, e.g., pearlescent materials such as bismuth oxychloride, guanine and titanium dioxide coated mica, preservatives such as benzyl alcohol, methyl paraben, propyl paraben and imidazolidinyl urea; and sequestering agents such as disodium ethylenediamine tetraacetate.

An amide is a preferred optional component present in the shampoo composition. Any ofthe alkanolamides of fatty acids useful in shampoo compositions can be used. Generally, these include mono and diethanolamides of fatty acids having from about 8to about 14 carbon atoms. Preferred compounds include coconut monoethanolamide, lauric or coconut diethanolamide, and mixtures thereof. The amide is present at a level of from about 1.0% to about 40%. It is believed that a more richer lathering, more stable product results when amides of these types are combined with the other components of the invention at hand.

Minor ingredients such as perfumes, dyes and coloring agents can also be added to the instant compositions to improve their consumer acceptability. If present, such agents generally comprise from about 0.1 % to 2.0% by weight of the composition.

The shampoos herein are preferably in the form of liquids orcreams in which water is the principal diluent.

The level of water in the compositions is typically from about 35% to about 90% byweight.

The shampoo compositions have a pH generally in the range from about 3to about 8. Preferred compositions are acidic however, highly preferred compositions having a pH in the range from about 3.5to about 6.5, especially from about4to about 6. The pH is measured on a 1% solution basis. A preferred pH regulating agent is a citric acid/sodium citrate buffer. Otheracidulating agents such as phosphoric acid, succinic acid etc. can also be used, however.

In use, the shampoo composition is normallyappliedto prewetted hair in an amountoffrom about 1 to about 60, preferably from about 5to about 30g per application, the hair is rinsed, a rinse conditioner maythen be applied in an amount of from about 1 to about 60, preferably from about 5 to about 30g per application, and finally the hair is rinsed again.

The following Examples further describe and demonstrate the preferred embodiments within the scope of the present invention. Unless otherwise indicated, all percentages herein are by weight of the shampoo or conditioner composition respectively.

In the Examples which follow, the abbreviations have the following designations.

ZPT1 ZincPyridinethione Median Equivalent Spherical Diameter = 5.4 microns Mean Sphericity = 0.25 ZPT2 ZincPyridinethione Median Equivalent Spherical Diameter = 1.25 microns Mean Sphericity = 0.75 ZPT3 Agglomerated Zinc Pyridinethione - 20% having an equivalent spherical diameter of at least 5 microns ZPT4 Zinc Pyridinethione platelets - medium equivalent spherical diameter of about 13 microns TMPP 1 -hydroxy-4-methyl-6-(2,4,4-trimethyl pentyl)-2-(1 H)-pyridone, triethanolamine salt NH4AS Ammonium C12 alkyl su If ate (29% aq. sol n.) TEA AS TriethanolamineC12alkyl sulfate (35% aq. soln.) NH4 AE2S Ammonium C12 alkyl (EO)2 sulfate (24% active) AGS Sodium alkyl glyceryl ether sulfonate (60%) MEA Coconut Monoethanoamide DEA Lauric Diethanolamide LS Sodium N-lauroyl sarcosinate CSA N-Cocoyl SarcosineAcid EGDS Ethyleneglycol distearate SCS Sodiumcumenesulfonate Exampleslto VII The following shampoo compositions are prepared:: Shampoo I 11 111 IV V VI VII Composition ZPT1 - - - - 1 1 ZPT2 - 1 - - - - - ZPT3 - - 1 - - - - ZPT4 1 - - 1 - - 1 TMPP 1 1 NH4AS 55 - - - 28 45 25 TEA AS - 50 - 55 - - NH4AE2S - 3 - - 40 2 35 AGS - - 60 - - - - MEA 3 2 - 3 4 3 2 DEA - - 2 - - - - LS - - 12 - - - - CSA - - 1 - - - EGDS 5 4 3 5 3 5 5 SCS 2 1.5 3 1 1.5 2 1 Sodium Citrate 0.5 0.5 0.6 0.8 0.7 0.8 0.5 Citric Acid 0.2 0.2 0.3 0.6 0.4 0.5 0.2 Coloursolution 0.1 0.1 0.12 0.2 0.1 0.1 0.1 Perfume 0.5 0.3 0.5 0.6 0.5 0.5 0.5 Water To 100% The shampoo compositions are prepared as follows. AIl materials except the preservative, perfume and antidandruff agent are added to the water maintained at a temperature offrom 65 Cto 74 C. The mix is then cooled to 380C in a heat-exchanger atwhich pointthe antidandruff agent is added. The mix is then further cooled to 27"C atwhich pointthe preservative and fragrance are added.

The shampoo compositions provide improved antidandruffefficacytogetherwith excellent storage stability and viscosity control.

Claims (18)

1. An antidandruff shampoo composition comprising: (a) from 5%to 50% byweightof surfactantselectedfrom anionic, nonionic, amphoteric, zwitterionic and cationic su rfactants and mixtures thereof, (b) from 0.1%to 5% by weight of a water-insoluble salt of 1-hydroxy-2-pyridinethione (I), and (c) from 0.1%to 15% by weight of a diffusion promoter selected from the water-soluble salts ofcumene sulfonic acid.

2. A composition according to Claim 1 having a Haake viscosity at 20"C (68"F) and 4 sec-' of at least 1500 cP, preferably at least 2000 cP, more preferably at least 2500 cP, and a Haake viscosity at 20"C (68"F) and 40 sec- which is at least 500 cP, preferably at least 1000 cP less than the 4 sec-l Haakeviscosity.

3. A composition according to Claim 1 or 2wherein the concentration of antidandruffagentdiffusing through a Spectropore semipermeable cellulose membrane in 60 min at 1% antidandruff agent concentration and 1 OO"F (37.8"C), is at least4 ppm, preferably at least 7 ppm.

4. A composition according to Claim 3 wherein the concentration of antidandruff agent diffusing through the membrane is at least 50% greaterthan in the absence of the diffusion promoter.

5. Acomposition according to any of Claims 1 to 4wherein the diffusion promoter is sodium cumene sulfonate.

6. A composition according to any of Claims 1 to Swherein the surfactant is an anionic surfactantselected form alkyl sulfates, ethoxylated alkyl sulfates and mixtures thereof.

7. A composition according to Claim 6 wherein the anionic surfactant is selected from ammonium alkyl sulfates, ammonium ethoxylated alkyl sulfates, and mixtures thereof.

8. Acomposition according to any of claims 1 to 7 wherein the pyridinethione (I) is selected from zinc,tin, magnesium, aluminium, cadmium, zirconium and sodium salts of 1-hydroxy-2-pyridinethione.

9. A composition according to claim 8 wherein the pyridinethione (I) is the zinc salt of 1-hydroxy-2-pyridinethione.

10. A composition according to any of claims 1 to 9 wherein the pyridinethione (I) has a particle size, defined as the mass median equivalent spherical diameter, of at least 1 micrometre.

11. A composition according to claim 10 wherein the pyridinethione (I) has a particle size in the range from 2 to 15 micrometers.

12. A composition according to any of claims 1 to 11 wherein the pyridinethione (I) is in the form of predominantly flat platelets having a mean sphericity of less than 0.65.

13. A composition according to any of claims 1 to 12 wherein the pyridinethione (I) is at least partly in agglomerated form.

14. A composition according to claim 13 wherein at least 20% ofthe pyridinethione (I) is in the form of agglomerates having an equivalent spherical diameter of at least 5 microns.

15. Acomposition according to any of claims 1 to 12 having a pH (1% aqueous solution) in the rangefrom 3.5 to 6.5, preferably from 4to 6.

16. A composition according to any of claims 1 to 15 additionally incorporating a non-polymeric, non-clay suspending agent.

17. A composition according to claim 16 wherein the suspending agent is selected from C16-C22fatty acid esters of glycerol or ethylene glycol, C16-C22fatty acid alkanolamides, C16-C22fatty acid amido alkylamines and C16-C22 alkyl amineoxides.

18. An antidandruff shampoo composition comprising (a) from 5%to 50% byweight of surfactant selected from anionic, nonionic, amphoteric, zwitterionic and cationic surfactants and mixtures thereof, (b) from 0.1% to 5% of a water-insoluble salt of 1-hydroxy-2-pyridonethione (I) (c) from 0.1% to 15% of one or morewater-soluble salts of cumene sulfonic acid.