Evaluating Cosmeceutical Efficacy

Image analysis

One of the more popular claims currently being made for many cosmeceuticals is that they are ‘antiaging and help restore a more youthful skin’, or words to that effect. One highly desirable outcome of such a treatment would be to reduce the appearance of facial wrinkles, such as those in the crow's feet region. Although such changes can be documented by standardized clinical photographs, it is more desirable to cast a replica of the skin surface by using a silicone rubber impression material, such as Silflo. Figure 3.1 shows representative specimens obtained from individuals with varying degrees of photodamage; the differences in wrinkle depth are readily appreciated. However, by using optical profilometry one can objectively measure changes in skin surface topography due to effective cosmeceutical treatments. This technique involves analysis of a digital image taken of a replica that is illuminated at a fixed, low angle. This causes the surface topography to be highlighted or shadowed in such a way that an image can be generated and subsequently analyzed for wrinkling, roughness, and other textural features ( Fig. 3.2 ).

This is but one example of how computerized image analysis can be used to objectively extract quantitative information from images. Box 3.1 provides a listing of some of the more common applications of image analysis that have been used to study skin structure and function. The basic rule applies that anything which can be seen by the unaided eye can easily be measured. Moreover, by using specialized lighting techniques, such as polarization or Wood's lamp illumination, things which cannot be directly visualized can be detected and measured via imaging.

Skin coloration

Another important visual clue to the condition of the skin after cosmeceutical application is its color, which depends upon a number of factors, including pigmentation, blood perfusion, and desquamation patterns. Experienced dermatologists frequently use color information in several ways. First, they can certainly appreciate the distribution of erythema and/or pigmented lesions on the basis of color. Moreover, by evaluating changes in the hue and/or intensity of color over time, they will be able to tell if patients are responding to treatment or not. Although the human eye is very sensitive, especially in detecting very subtle differences in contrast, the evaluation of color is still highly subjective. Color-measuring devices offer the advantages of objectivity and quantification on a continuous scale that can be referenced to color standards.

The devices that are currently being employed in experimental dermatology, skin pharmacology, toxicology, and cosmetic science to measure skin color changes fall into two distinct types of instrument, as shown in Box 3.2 . In one category we have the tristimulus colorimeters, which are based on the three-dimensional L*a*b* color space (CIELAB). L*a*b* allows any color to be mathematically described by its hue (position on the color wheel), value (lightness), and chroma (saturation). These would include the Minolta ChromaMeter and the MicroColor of Dr. Bruno Lange GmbH, which have seen widespread use for the quantification of erythema in the study of irritant dermatitis due to exposure to detergents, topical corticoid activity in the vasoconstriction test, and for measuring the percutaneous penetration of vasodilators such as nicotinic acid.

Other types of instrument include the Mexameter (Courage + Khazaka), which is based on the two-wavelength method of . This instrument emits green and red light and measures the reflected light from the skin surface. Because changes in skin redness will greatly affect the absorption of green light but will have very little effect on that of red light, an erythema index can be calculated. Since increased melanin pigmentation will lead to an increased absorption of both red and green light, a melanin index can be computed in a similar fashion.

More recently, colorimeters have been developed, such as the DSM II (Cortex), using white LED illuminants ( Fig. 3.3 ). These newer models provide a measurement of the L*a*b* and RGB color spaces and will calculate both erythema and melanin indexes. Due to the consistency of the illumination in these models, measurements are more reliable and reproducible. The reproducibility is partially due to the fact that the probe is very lightweight, and has a clear probe tip so the exact area to be measured can be seen before taking the measurement.