Human Body Skin
Paul J. Matts, Ph.D1; Angela J. Long, PhD1; Colin Williamson, BSc1; Rene C. Rust, Ph.D1 ;
1The Procter & Gamble Company, Rusham Park Technical Centre, Egham, Surrey, UK
The total body skin surface area for an average adult human covers approximately 2m2. It is, therefore, not surprising that within this expanse of tissue there is a wide variety of environmental exposure and mechanical stress (the extremes expressed, for example, in skin covering structures such as knees / elbows / heels) and, thus, (a) a concurrent distribution of different structural and functional profiles and (b) a corresponding variety of maintenance needs.
The objective of this piece of work, therefore, was to investigate actual perception of these differences in body skin amongst US consumers and relate these to reliable data for stratum corneum properties across different anatomies.
To investigate consumer perception of differences in body skin, we performed largebase research amongst a representative group of 316 US females aged 18-65 with normal (non-diseased) skin.
Two simple, yet extremely important, insights emerge: (a) consumers view body skin as fundamentally different to face skin, principally because of incidence of "dryness" (and related endpoints) (b) body skin is not the same - specific regions were perceived to represent "torture test" areas of extreme dryness (e.g., heels, elbows, knees). The vast majority of women questioned (85%) were concerned by these areas, 63% stated that they were accordingly self-conscious and almost half (47%) agreed that, as a result, this caused them not to wear certain clothes or shoes.
How does the reality of these consumer insights relate to the structure / function of the skin compartment that, at once, drives "dryness"-related endpoints and is the cosmetic substrate available for everyday treatment - the stratum corneum (SC)? A study of the literature reveals a paucity in well-controlled comparative measurements of SC structure / function across different anatomies and those that do exist provide conflicting data (when comparing, for example, TEWL or capacitance values). The most rigorous recent study is that of Ya- Xian et al. (1999) who measured the number of corneocyte cell layers in the SC of fresh skin samples obtained from a wide range of body sites in >300 subjects. The data are shown adapted in Figs 4 and 5 and show how there is an obvious progression in SC thickness - head < trunk < limbs < extremities (heels, etc.). These may be clustered into three main anatomies (Fig. 5) - face, body and extremities. Focussing on the SC, therefore, thickness of this layer appears to correlate very well with consumer-perceived skin condition across the body (compare Figs. 1 & 4), providing an intuitive segmentation of need / biology. SC condition is driven principally by internal water gradient and perhaps it is no great surprise, therefore, that SC thickness (itself a function of genetics and mechanical abrasion received relative to position on the body) should drive relative expression of dryness endpoints (and consequent consumer perception).
p> Large-base body-site-specific consumer research has highlighted (a) significant perceived differences in body skin and (b) an apparent concurrent reduction in quality of life, driven particularly by marked dryness expressed in the extremities (i.e., heels, knees, elbows, etc.). Whilst new technologies offer new standards of care for body skin (cf. our "Breaking the Dry Skin Cycle" poster), these insights highlight the need for technology to address specifically these areas. It is proposed that treatments that target and are tailored to the unique structure of the SC in these areas (i.e., marked thickening) will provide greatest benefit in breaking the dry skin cycle. Thus, the penetration, humectancy, bio-activity / bioavailability of product excipients will be critical in the design of such a specialised product.Ya-Xian, Z., Suetake, T and Tagami, H., Number of layers of the stratum corneum in normal skin - relationship to the anatomical location on the body, age, sex and physical parameters, Arch. Dermatol. Res., 291:555-559, 1999