Creative Developments (Cosmetics) Limited

Antiperspirants & Deodorants: SPC 2002

John Woodruff

As their name implies, antiperspirants inhibit perspiration and because they affect the structure and function of the body they are considered drugs in the USA and are sold as licensed products. Deodorants either mask body odour with perfume, or absorb perspiration or inhibit the activity of gram +ve bacteria, which cause body malodour; they are regulated as cosmetics. In Europe both antiperspirants and deodorants are considered cosmetics. The only truly effective antiperspirant actives are aluminium salts like aluminium chlorohydrate, aluminium zirconium chloride hydroxide complexes [Al_xZr(OH)Cl₂] and aluminium zirconium chloride hydroxide glycine complexes. The composition and use of aluminium zirconium complexes is regulated in the EU.

Despite the rather limited number of actives available to control perspiration it is a product area that attracts much patent activity and a review of those recently issued reveals trends in the antiperspirant market. There are three classes of antiperspirant sticks, namely suspension sticks, emulsion sticks and solution sticks. Suspension sticks contain a particulate antiperspirant active material suspended in a structured carrier. Emulsion sticks normally comprise an emulsion of an oil phase and a hydrophilic phase containing the antiperspirant active in solution, the continuous phase being structured. In some emulsion sticks, the continuous phase is an oil phase. In solution sticks, the antiperspirant is typically dissolved in the liquid carrier phase, which is structured. The liquid phase can comprise water and/or a water-miscible organic solvent. The three categories can be applied to sticks of both firm and soft solids compositions.

USP 6,383,476 (P&G, May 7th, 2002) describes anhydrous antiperspirant and deodorant compositions that allow water-soluble skin active solids to rapidly release into the sweat or other moisture on the skin, thus enhancing their efficacy. The actives are not part of the antiperspirant system but are added to confer other benefits; niacinamide and its derivatives and also calcium pantothenate are given as examples of desirable additives. Calcium pantothenate in antiperspirants is the subject of other P&G patents and is claimed to soothe irritated skin and to promote wound healing, which often occurs with underarm shaving. The preferred form is a solid stick comprising an aluminium salt and a water-soluble active ingredient in particulate form in a carrier of dimethicone and cyclopentasiloxane with C13-14 isoparaffin. Hydrogenated rapeseed oil with C18-36 acid triglyceride provide structure to the final product and the following formula illustrates the concept.

(USP 6,383,476) Ingredients	%^w/w
Dimethicone (50cs)	5.00
Cyclopentasiloxane	60.80
AlZr Trichlorohydrex Glycinate (solid)	20.00
C13-14 Isoparaffin	10.00
Niacinamide (solid)	3.50
Calcium Pantothenate	0.50
Tocopherol Acetate	0.50
Perfume	0.75
C18-36 Acid Triglyceride	3.75
Hydrogenated Rapeseed Oil	15.00

Unilever Patent, USP 6,361, 766 (March 26th, 2002) describes anhydrous antiperspirant suspension sticks, which comprise an oxygen-containing emollient oil having a refractive index of at least 1.465, in conjunction with structuring wax or a non-polymeric fibre-forming gelling agent. Preferred emollient oils include alkyl benzoates and alkylphenylsiloxanes and the compositions are said to result in minimal white deposits on application. As an alternative to stick-type preparations, USP 6,387,358 (Unilever, May 14th, 2002) describes soft solid compositions that are extruded through multiple apertures in a dispensing applicator. The particulate antiperspirant active material is suspended in a continuous phase containing a water-immiscible liquid, which is structured by an organic polymeric thickener and a second fibre-forming structuring agent. One example uses 1% dextrin palmitate with 2.8% sucrose distearate and 5.7% behenyl alcohol. It is claimed it is possible to achieve a good combination of structural properties with a composition that gives only a low visible residue on skin and on clothing. The liquid portion is a combination of volatile and non-volatile silicones and liquid aliphatic hydrocarbons. Fatty acid esters may also be incorporated but fatty alcohols such as stearyl alcohol are preferably less than 5% of the composition since these lead to visible white deposits on application.

Not all anhydrous compositions are based on particulate antiperspirant actives; USP 6,399,049, (P & G, June 4th, 2002) describes a solubilised system based on glycerol butyl ether in combination with volatile and non-volatile silicones. It is said that the solubilised antiperspirant active provides good application and aesthetic characteristics and is less sticky during or after application and milder to the skin than typical non-solubilised systems. Also solutions of antiperspirant active with glycerol butyl ether are more compatible with non-polar solvents, which enables the formulation of clear or translucent antiperspirant compositions containing non-polar solvents such as volatile and non-volatile silicones. A simplified example formula follows

(USP 6,399,049) Ingredients	%^w/w
AlZr Trichlorohydrex glycinate (solid)	14.00
Glycerol butyl ether	36.00
Dimethiconol	35.00
Cyclopentasiloxane	15.00

This formula may be structured by the addition of suitable gelling agents such as esters of p-hydroxystearic acid, or stearamide or C18-36 acid triglyceride or mixtures of these.

Many other patents describe means of producing clear compositions, structured sticks and of introducing other actives and there is always an emphasis on smooth application, reducing stickiness and of minimising white deposits on skin and clothing. Regardless of the patent objective almost all incorporate every recognised aluminium salt as part of the antiperspirant system but few claim an improved activity. An exception is USP 6,375,937 (Colgate-Palmolive, April 23^rd, 2002) that claims aluminium zirconium salts which have a metal to chloride molar ratio in the range of 0.9-1.2:1 and a glycine:zirconium molar ratio greater than 1.3:1. Such ratios have to be within recognised limits as defined by 76/768/EEC. These are a maximum concentration of zirconium at 5.4% and the ratio of aluminium atoms to zirconium atoms must be between 2 and 10. Also the ratio of the number of (Al + Zr) atoms to chlorine atoms must be between 0.9 and 2.1.

It is claimed that the salts described by the USP 6,375,937 have improved efficacy and may be used in all product forms but it is preferred that the glycol content of the formulations be kept to a minimum. Various formulation ideas are given including stick products whereby 22% of the active in powder form is dispersed in cyclopentasiloxane and gelled with 21% stearyl alcohol and about 10% talc is added to improve the structure and feel. Dissolving the complex in water and emulsifying this with cyclopentasiloxane and dimethicone copolyol provide compositions suitable for roll-on application.

It is not always appreciated how varied the available materials described by single INCI names may be. Aluminium chlorohydrate is available with different ratios of aluminium to chlorine and as a 50% aqueous solution or as a fine powder of differing particle size. The solution is used for roll-ons and sprays whereas the powders are used in dry sprays and suspension-type applications such as the anhydrous products already described. Aluminium chlorohydrate can be complexed with zirconium salts to form synergistic compounds of enhanced efficacy and they are used in all non-aerosol forms of antiperspirants including clear hydro-alcoholic lotions, sticks and gels. For suspension products the particle size is closely controlled, as this is an important factor in those products containing particulate actives. Aluminium chlorohydrate/aluminium chlorohydrex PG complexes and aluminium - zirconium / aluminium - zirconium PG complexes are recommended for low-residue products, which are usually provided as clear products to emphasise their minimum whitening characteristics.

Many people prefer a deodorant to an antiperspirant and, as stated in the opening paragraph, they either mask body odour with perfume, or absorb perspiration or inhibit the activity of gram +ve bacteria, which cause body malodour. Perfumes that combine antimicrobial properties with masking effects have an obvious advantage but most essential oils that perform such a dual function have too strong an odour themselves. Many have been suggested including Melaleuca alternifolia (tea tree) oil, Coriandrum sativum (coriander) oil and Eucalyptus globulus oil. A vegetable protein extract, Saccharomyces ferment, from Carrubba, USA, is a water-soluble liquid derived from the fermentation of vegetable matter that contains a number of enzymes, which provide bio-conversion of a wide range of malodorous substances. The material converts the molecules responsible for malodours by enzymatic oxidation, reduction, neutralisation or substitution into less odorous forms. Its use is not limited to human body odours; it also converts mercaptans into sulphonates and oxidises hydrogen sulphide to the sulphate. It also promotes hydrogen bonding and van de Waals forces in low molecular weight materials thus reducing their volatility. Further details are available through the UK distributors, Chemlink.

Various materials have been suggested that absorb underarm perspiration; Neusilin UFL2 is a fine powder of magnesium aluminometasilicate from Miyoshi Kasei Group and available through S Black. It has a particle size ≤1.0 micron and a high surface area that promotes absorption of sebum and perspiration. It works by entrapping the triglycerides that are normally broken down by enzymatic action into the unsaturated short-chain fatty acids responsible for body odour. Any fatty acids that are present are strongly adsorbed to the particles surface. The deodorising action of Neusilin UFL2 is further enhanced by its magnesium ion content that effectively neutralises carboxylic acid groups. The suppliers stress that the material has no antimicrobial properties and is not an antiperspirant.

Inhibition of gram +ve bacteria is the third means of controlling body odour and for this purpose triclosan appears to be the most popular and effective material. However products containing it are prone to discolouration unless some simple preventative measures are taken; primarily the pH should not exceed 7.5 and the presence of a UV absorber is beneficial. Soap-based clear sticks should have a minimum content of sodium stearate and use non-transparent packaging. N-Acyl sarcosinate surfactants are said to enhance deodorant and antiperspirant activity by improving the substantivity of the active to skin and as little as 2% is said to be effective in this regard.

Arguably, the most important advance in antiperspirant and deodorant formulation was the introduction of silicone compounds as a principal constituent of the formulation. If carefully incorporated, they improve product application, confer a non-greasy skin feel and reduce whitening. It is more than twenty years since volatile silicones were first used as a replacement for ethanol in sticks and roll-ons and as seen in the illustrative patents, they are still to be found in the majority of products. Dow Corning (S Black) has recently introduced two formulation aids to complement 5225C and to further improve antiperspirant compositions. 5225C is a mixture of cyclopentasiloxane with a dimethicone copolyol (PEG/PPG 18/18 dimethicone) suitable for the preparation of w/Si and w/Si/w multiple emulsions and of clear systems. 9011 is a mixture of cyclopentasiloxane with PEG-12 dimethicone crosspolymer that reduces the need for high shear in the processing stage and is suitable for anhydrous compositions as well as w/Si and w/Si/w multiple emulsions and clear systems. It also circumvents some restrictive patents on the use of 5225C. Both materials support high levels of internal phase in w/Si emulsions. For w/o and water-in wax systems 5200 is recommended; this is lauryl PEG/PPG-18/18 methicone and it also has moisturising properties.

Finally, there are many stories on the web attacking various cosmetic products and cosmetic ingredients; they are usually being used to promote an alternative composition. “Antiperspirants cause breast cancer” is the headline but for anyone that needs to reply to enquiries about this the American Cancer Society has issued a statement that it is not aware of any epidemiological studies reporting a statistical association between breast cancer risk and antiperspirant use. Likewise, it is not aware of any evidence that aluminium or any of the other chemicals in antiperspirants are mutagenic (cause DNA damage that can lead to cancer). It concludes that products such as antiperspirants are rigorously tested and evaluated by the FDA before they can be marketed.