Optimization of emollients by selecting suitable excipients
Vaseline is a widely used basic constituent of emollients despite its to some extent unfavourable cosmetic properties. One reason for this is its high occlusivity and very good compatibility with other components of the formulation. Only vaseline is capable of reducing the loss of moisture from the skin by up to 50 %.
This is especially important on areas of skin exposed to heavy stress, such as the hands, the cutaneous lipids of which frequently come into contact with solvents and surfactants. A good emollient usually has pronounced oil restorative properties. But only the interplay between skin lipids and hydration of the horny layer provide optimal skin protection. Another factor is the preservation or restoration of a sufficient layer of skin lipids. This can preferably be achieved using lipids with affinity for the skin, which due to their polarity enter into strong interactions with the intercellular lipids of the skin and can thereby provide physiological protection, moisture and conditioning.
Besides meeting the requirements of safety and efficacy, it is also important for emollients to be cosmetically attractive. In commonly available cosmetics this is achieved by combining a large number of excipients with different feel properties. The goal of medically oriented development of emollients should be not only to achieve positive sensory characteristics and a good conditioning effect, but also and especially the best possible tolerability. This can and must be achieved by using a small number of carefully selected, toxicologically characterized excipients of high purity. The use of multifunctional excipients in the development of emollients thus affords a good opportunity to combine a minimum number of substances into a stable formulation which guarantees a high level of skin hydration while retaining good application characteristics. Furthermore, all known allergens should be excluded in order to develop formulations of high tolerability. These include especially preservatives and fragrances which are often responsible for causing allergies. The use of classical preservatives may under some circumstances be unnecessary when excipients are judiciously chosen. Since microbiological stability is a paramount consideration for cosmetics, a wide selection of mutually complementing preservatives is generally used in these products. Since the legal regulations do not require the submission of a rationale for the type and quantity of preservatives used in cosmetics, many cosmetics contain relatively high doses of these substances in order to rigorously prevent the growth of microorganisms in the event of microbial contamination. The non-inclusion of preservatives mandates very close monitoring of the microbiological stability and, for aqueous products, invariably the use of an alternative form of preservation. Some products are now on the market which instead of the classical preservatives incorporate higher doses of alcohols and glycols (propylene glycol, pentylene glycol etc.). This type of substitution, however, introduces the risk of irritations and encourages the penetration of undesired excipient constituents because of the solvent properties of these substances, which are also able to easily through the skin.
For development and manufacture in the pharmaceutical industry, quality standards are applied that are advantageous for the development of pure, reliable and effective medical skin care. Pharmaceutically oriented product development will therefore concentrate on the essential characteristics of excipients and attach great importance to product sustainability and safety. These activities should satisfy, among other criteria, the following requirements which are self-evident for medicinal products:
- Selection of pharmaceutical grade excipients (substances specified and tested according to medicinal product guidelines)
- Qualification of suppliers (e.g. audit, documentation review)
- Release of active ingredients based on pharmaceutical test specifications and quality specifications
- Additional filtering of lipid components during and after manufacture
- Permanent quality testing and assurance
- Comprehensive documentation and change control (monitoring of changes to formulations and manufacturing procedures)