Читать книгу Cosmeceuticals - Группа авторов - Страница 36

Many believe the active ingredient of a cosmeceutical formulation accounts for the majority of the efficacy. This is not correct. The moisturizer vehicle probably accounts for at least 75% of the product efficacy. Not only can the moisturizer create a smooth soft film over the skin surface, it can also reduce transepidermal water loss (TEWL), which reduces the fine lines of dehydration, especially noticeable around the lateral eyes. This is accomplished through the application of occlusive and humectant substances.

Occlusive substances place an oily film on the skin surface that is more or less impermeable to water. Highly occlusive substances, such as petrolatum, mineral oil, paraffin, lanolin, and carnauba wax, significantly reduce water loss, but are sticky and provide poor compatibility with colored cosmetics [3]. Aesthetics are a very important part of cosmeceuticals. For this reason, most cosmeceutical formulations include less occlusive but also less greasy substances, such as silicone derivatives (dimethicone, dimethiconol) and polymers (acrylates). Many of the botanically based formulations will include jojoba, hemp, borage, or evening primrose oils.

Occlusive agents must be combined with humectants to not only stop water from leaving the skin, but also to rehydrate the skin by attracting water. Humectants have been used in cosmetics for many years to increase shelf life by preventing product evaporation and subsequent thickening due to variations in temperature and humidity. Humectants act like sponges in the skin to hold water with the natural major skin humectant being hyaluronic acid, which is also used as a humectant in cosmeceutical preparations. Other common humectants include glycerin, sodium lactate, urea, propylene glycol, sorbitol, pyrrolidone carboxylic acid, gelatin, vitamins, and some proteins [4, 5].

Finally, emolliency is an important concept in cosmeceutical efficacy. Emollients smooth down desquamating corneocytes to make the skin surface appear smooth and feel soft, which are very important consumer-perceived cosmeceutical benefits [6]. In addition, some emollients are also occlusive moisturizers. Important to consumer satisfaction with a moisturizing product since smooth skin is expected following application, even though emolliency may not necessarily correlate with decreased TEWL. Emollients function by filling the spaces between the desquamating skin scale with oil droplets, but their effect is only temporary. Commonly used emollients include propylene glycol, isopropyl isostearate, octyl stearate, and isopropyl myristate [7].

Most cosmeceutical moisturizers consist of water, lipids, emulsifiers, preservatives, fragrance, color, and specialty additives. Most cosmeceuticals are 60–80% water with the water functioning as a diluent, rapidly evaporating after application. Emulsifiers are generally detergents in concentrations of 0.5% or less, keeping the lipids emulsified in the water to form one continuous phase. This then means the specialty additives become the differentiating factor between various cosmeceutical moisturizer products. In summary, a cosmeceutical moisturizer formulation must increase the water content of the skin (moisturization) and make the skin feel smooth and soft (emolliency).