Cosmetic products stability

D Miller, EM Wiener, A Turowski, C Thunig, H Hoffmann. O/W emulsions for cosmetic products stabilized by alkyl phosphates rheology and storage tests. Colloids Surfaces A Physicochem Eng Aspects 152(1-2) 155-160, 1999. 

Branched-chain acids have a wide variety of industrial uses as paint driers (7), vinyl stabilizers (8), and cosmetic products (9). Cobalt and manganese salts of 2-ethyIhexanoic acid and neodecanoic acid are used as driers for paint, varnishes, and enamels litbium, magnesium, calcium, and aluminum salts of 2-ethyIhexanoic acid are used in the formation of greases and lubricants (see Driers and metallic soaps). Derivatives of isostearic acid have been used as pour point depressants in two-cycle engine oils, as textile lubricants, and in cosmetic formulations. Further industrial appHcations can be found (10). 

The applications of a-sulfo fatty acid esters are widely spread as for other surfactants. They can be used in detergents, cleansers, and cosmetic products as well as in the building industry and for the production of synthetic materials and agrochemicals. The main properties for these applications are surface activity, wetting ability, hard water stability, lime soap dispersion power, and good human and environmental safety profiles. 

Surfactants are useful in formulating a wide variety of disperse systems. They are required not only during manufacture but also for maintaining an acceptable physical stability of these thermodynamically unstable systems. Besides the stabilizing efficiency, the criteria influencing the selection of surfactants for pharmaceutical or cosmetic products include safety, odor, color, and purity. 

Pope DG. Accelerated stability testing for prediction of drug product stability. Drug and Cosmet. Ind., Part 1, 54-62, November, 1980 and Part 2, 48-116, December 1980. 

Barium sulfate is a stable inorganic material that has been used for contrast media or cosmetic products because of its stability. Since a negative external electric potential accelerates skin barrier repair after barrier disruption, we hypothesized that topical application of barium sulfate would affect the skin barrier recovery rate, depending on the f potential. 

Moisturizers and other similar stay-on products have often pH between 4 and 6. That pH-range is similar to skin surface pH and is often suitable for good physical stability of the cosmetic product. However, there are several moisturizing creams with world-wide acceptance, which have pH of about 7 or even 8, for example, those with stearic acid as the main emulsifier. Also skin protectants based upon zinc oxide often have an alkaline pH. 

In addition, new technology is available, which uses the gel-state PC matrix for stabilizing a formulation containing not only metabolites but also emollients free of surfactants, perfumes, and preservatives. This new technology is used for the preparation of Physiogel AI (Stiefel Laboratories), a new cosmetic product in the market in several European countries. Physiogel AI contains the following metabolites ... 

First a coarse O/W emulsion is prepared and, on heating, phase inversion occurs. After cooling down through the microemulsion zone, the finely dispersed nature of the microemulsion is partially retained and emulsions with drop sizes of about 100 nm result [28-30]. They show considerable long-term stability as a consequence of the Brownian motion of the oil droplets [31] and pump sprayable deodorants are one of the cosmetic products based on this technology. 

The demands on product stability and manufacturing practices are essentially the same for cosmetics and drugs. 

In topical cosmetic and toiletry applications, xylitol is used primarily for its humectant and emollient properties, although it has also been reported to enhance product stability through a combination of potentiation of preservatives and its own bacteriostatic and bactericidal properties. 

Product stability and performance can be affected by exposure to several oxidative sources, including oxygen, free radicals, UV radiation, oxidative enzymes, catabolic oxidation, and chemical oxidation. Many antioxidants are also good UV absorbers due to their conjugated chemical structure. Typical antioxidants found in cosmetic products are flavonoids, polyphenols, carotenoids, thiols, tocopherol (vitamin E) and ascorbic acid (vitamin C) [71,72], According to Black [73], a combination of antioxidants from different classes is more effective than a single antioxidant due to an antioxidant cascade mechanism. 

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