Deciphering Temporary Hair Depilation Formulas

By: Eric S. Abrutyn, TPC2 Advisors Ltd., Inc.

Posted: December 29, 2010, from the January 2011 issue of Cosmetics & Toiletries.

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Although depilatory hair removal has remained relatively constant for the past few years, current trends are to develop more naturally based depilatory agents, less irritating formulas, or to affect the hair growth cycle. Following are a few of the more recent patents issued in the depilatory category. Structured depilatory compositions: The applicants of this patent sought to combine favorable rheology and the aesthetics of a structured system with a depilatory active, resulting in a depilatory composition that is aesthetically pleasing, is phase-stable, and that exhibits one or more additional properties such as easy wash-off and/or mildness.¹ Specifically, the patent inventors have addressed the belief that aggressive depilatory actives combined with high levels of electrolyte, which are required to augment the efficacy of the depilatory, make it difficult to form a stable structured depilatory composition. By combining at least one depilatory active with at least one surfactant, the new composition yields a desirable attribute known as heaping, i.e. the ability to recover shape rapidly and form peaks when subjected to shearing. Any variety of suitable surfactants including anionic surfactants may be used in the compositions of the present invention, preferably such that the final composition has either a yield stress from approximately 1—1500 Pa and/or and Hauesorff-Besicovitch dimension of less than approximately 1.7.

Endothelin active for depilation: This invention relates to depilatories and external preparations containing endothelin or its agonist, and also to a depilating method characterized by administering endothelin or its agonist.² Endothelin is a peptide composed of 21 amino acid residues that, to date, is known to include three iso-forms: endothelin-1, endothelin-2 and endothelin-3. Endothelin is a physiologically active substance that directly or indirectly causes persistent contraction of vascular and non-vascular smooth muscles. In recent years, the role of endothelin in ontogenesis has been tied to various cells such as gliacytes, renal mesangial cells and melanocytes. The depilatory effects of endothelin in the present invention are based on inhibiting hair growth by transitioning hair follicles from the growth phase (anagen) to the regression phase (catagen).

In addition to endothelin, one or more ingredients having hair growth inhibitory and/or depilatory effects, such as keratolytic agents and thioglycolic acid and salts thereof, may be added to the depilatory and external preparation. Examples of the keratolytic agents can include lactic acid, salicylic acid, glycolic acid, citric acid and malic acid.

Non-irritant, rapid-action depilatory composition: This patent discloses a rapid-acting, non-irritating depilatory that reduces exposure time by utilizing a high pH composition. The composition consists of at least one bisulphite and/or sulphite compound of an aldehyde or ketone such as: acetaldehyde, propionaldehyde, butyraldehyde, benzaldehyde, glyoxal or glyoxylic acid, and an organic reducing agent in a cosmetically acceptable medium. It has been found that the reducing action of the bisulphite and/or sulphite compound responds to the organic reducing agent, encouraging the reaction of free sulfur-hydrogen groups in hair’s cysteine units and thus making rapid solubilization of keratin and faster hair removal possible. In addition, improved depilatory activity was observed when the acid components of the composition were in a salt form such as sodium, potassium, strontium, calcium, magnesium and arginine, with a strong organic base such as guanidine, hydrazine or hydroxylamine to increase the denaturing power—requiring an approximate 6–13.5 pKa.³

Enzyme inhibition for reduced hair growth: According to this patent, the rate and character of hair growth can be altered by applying inhibitors of certain enzymes such as 5-alpha reductase, ornithine decarboxylase, S-adenosylmethionine decarboxylase, gamma-glutamyl transpeptidase and transglutaminase to skin. Specifically, a method is disclosed for reducing unwanted hair growth by applying to the skin an agonist of farnesoid X receptor in an effective amount. Farnesoid X receptor, also referred to as FXR, RIP14, bile acid receptor, BAR, HRR1 or NR1H4, is a member of the family of ligand-activated transcription factors that binds to specific cis-acting regulatory elements and modulates gene expression. These receptors bind as dimers of either two molecules of the same receptor (homodimers) or one molecule each of two different receptors (heterodimers).