Читать книгу Cosmeceuticals - Группа авторов - Страница 37

Most cosmeceuticals are evaluated prior to marketing to be sure they meet formulation efficacy goals. Since invasive biopsy analyses are not appropriate, given that drug-like effects could be demonstrated, cosmeceuticals are tested with noninvasive methods. These noninvasive methods include regression analysis, profilometry, squametry, in vivo image analysis, corneometry, and evaporimetry [8].

Regression analysis is an important method to determine if a moisturizer can produce benefits even after application has been discontinued. A good cosmeceutical moisturizer will maintain some benefits 48 h after the product was applied. Most regression studies will have the subjects apply the facial cosmeceutical for 2–4 weeks followed by discontinuation. The skin will be evaluated at the end of the study period; subjects will discontinue application, return to the research center 48 h after the last application, and undergo evaluation [9]. This method is particularly valuable since the efficacy of all moisturizers is excellent immediately following application, but true effectiveness can only be assessed based on the longevity of benefits [10].

The minimization of fine lines and wrinkles is a commonly purported cosmeceutical benefit. One noninvasive method used to document wrinkle reduction is profilometry, which involves the analysis of silicone replicas of the skin surface with scanning laser imaging. The unpolymerized silicone, which is the same as dental impression material, is mixed with the catalyst. The silicone is placed over the skin surface to create a negative replica of the skin texture. Analysis of these replicas before and after application of the cosmeceutical can determine the ability of the product to minimize wrinkles and support wrinkle reduction claims [11].

Many cosmeceutical moisturizers claim to smooth the skin surface or uncover younger skin through exfoliation. Exfoliation removes nonliving corneocytes from the skin surface, which is a cosmetic effect, by using ingredients that digest the intercellular bonds. Ingredients capable of inducing exfoliation include glycolic, lactic, malic, and salicylic acids. While the appearance of exfoliated skin can be seen and felt, squametry is a noninvasive technique that can be used to demonstrate enhanced exfoliation. With this technique, a sticky round tape, known as a D-squame, is pressed against the skin surface with a constant pressure plunger for a count of 10. The D-squame is then removed with forceps and placed on a black backing card. The opacity of the tape, which increases as more skin scale is removed, is compared against a photonumeric reference card to provide an ordinal rating for the amount of skin scale that was removed. Limited skin scale indicates the cosmeceutical induced little exfoliation, while more skin scale indicates a greater exfoliant benefit [12]. The D-squame technique is a valuable noninvasive efficacy assessment for exfoliation.

Visible cosmeceutical efficacy can be assessed with the human eye, but more subtle effects can be observed with in vivo image analysis utilizing a video microscope [13]. Care must be taken to standardize lighting and camera angles to insure accurate comparison images. The use of a video microscope may be of limited value in assessing cosmeceutical efficacy, however. If the human eye cannot see improvement and only the video microscope images can detect benefit, will the consumer continue using the cosmeceutical without visible results? This is always a challenge when evaluating cosmeceutical efficacy.

As mentioned earlier, skin water content is important to skin appearance optimization. A major cosmeceutical benefit is to decrease the amount of water leaving the skin and increase the amount of water in the skin. These two benefits can be measured through noninvasive equipment. The amount of water leaving the skin, known as TEWL, can be measured through evaporimetry [14, 15]. This technique uses a probe containing two humidity meters at a known distance apart placed above a collecting chamber of known diameter. The probe is placed in contact with the skin for 1 min and the amount of humidity measured is collected until a steady state is reached. This allows determination of the amount of water lost by the skin over a certain area in a fixed period of time. Lower TEWL could be a major benefit of a facial cosmeceutical moisturizer. In addition, the amount of water in the skin can also be assessed with a technique known as corneometry [16]. Corneometry puts a lower level electrical current into the skin, which is conducted by water between the sending probe and receiving probe. The amount of electricity conducted by the skin is directly proportional to the amount of water in the skin. A higher number is indicative of superior moisturization.