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Cosmetics and Skin Care in Dermatology at a Glance
 Nonmedical skin care and cosmetic use of over-the-counter products represent a major growth area among consumers.Understanding variations in skin types using a new system of classification facilitates patient selection of over-the-counter products.Cosmetics and skin-care products can be a source of a range of adverse reactions including irritation and allergy.

According to recent data, the US sales of skin-care cosmeceuticals (cosmetics with attributed biologic effects) range between $3.5 and$6.4 billion, with forecasts of steady continued growth despite the global recession.13 A plethora of skin-care products are currently available to account for this substantial sales volume. The range of products and their associated claims is so extensive and complex that physicians and consumers are often confused about their indications and effectiveness. One approach to understanding these many options is to consider how the products are used to treat specific skin types.

For the purposes of choosing the most appropriate cosmetics and other skin-care products, facial skin can be grouped into four main categories that in practice represent up to 16 skin types: dry (D) or oily (O), sensitive (S) or resistant (R), pigmented (P) or nonpigmented (N), and wrinkled (W) or unwrinkled [or “tight” (T)]. These “skin types” are not static and can be affected by a range of intrinsic and extrinsic factors such as environment, aging, and disease. The key to proper skin-care recommendations is to take all four parameters into consideration. The various permutations of the four skin-type parameters yield 16 possible skin types. For example, a person may have dry, sensitive, pigmented, wrinkled skin, and her needs would significantly differ from someone with oily, sensitive, pigmented, and wrinkled skin.

This chapter discusses the basic science and defining characteristics of the four parameters. Certain extrinsic or intrinsic factors, such as a move to a different climate, a change in stress levels, pregnancy, menopause, and other stressors, can result in a skin type change. The Baumann Skin Type Indicator, a questionnaire developed to determine skin type, is helpful in assessing skin type initially and again after major life events.4

## Oily versus Dry

Xerosis or “dry skin” describes skin that is characterized by dull color (usually gray white), rough texture, and an elevated number of ridges.5 The etiology of this common condition is multifactorial. The most significant factor in the development of xerosis is the role of the stratum corneum (SC) and its capacity to maintain skin hydration. Rawlings et al showed that patients with dry skin have a perturbation in the lipid bilayer of the SC, which is associated with increased fatty acid and decreased ceramide levels.6 Defects or deficiencies in this barrier layer of the skin cause a spike in water evaporation, known as transepidermal water loss (TEWL). This leads to abnormal desquamation of corneocytes7 because desmosomes remain intact at ...

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