Massage & Bodywork

September/October 2012

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Since these then we will look at some research behind skin- to-skin transference: the unintentional absorption of another person's topical medication. SKIN: A NATURAL BARRIER Our skin forms an excellent barrier to the outside world, maintaining the integrity of our internal environment while limiting absorption. It accomplishes this task at several levels. The first functional barrier is the most superficial layer, the stratum corneum. It contains a complex arrangement of keratinocytes (dead skin cells that have been filled with waterproofing keratin), lipids, proteins, and cementing materials. When we develop a callous on our hands or feet, it is the stratum corneum that thickens. This layer also blocks penetration of most substances into deeper layers, while retaining skin hydration. Deep to the stratum corneum, several other epidermal layers contain the skin's sensory and immune cells. Sensory cells detect touch, temperatures, pressure, and pain, thus alerting us to possible skin injury and pathogenic invasion. The thickness of the epidermis is quite consistent across most body areas. Hands and feet have an extra layer, the stratum lucidum, which offers protection from sheering forces and friction. The stratum lucidum may also help with protection from absorption by being an extra barrier. By contrast, the thickness of the dermis and adipose layers of the skin varies greatly across body areas, and by age and gender; skin thickness over the eyelid is very thin compared to skin over the abdomen, for instance. Infants and elders have thinner skin compared to adults.1 Men have thicker skin compared to women, although no evidence that this influences barrier function has been found. As functional as it is, skin is not completely impermeable. The stratum corneum limits absorption of most substances, but some compounds are able to penetrate through the epidermis to various skin depths. For example, most sunscreens are designed to remain within the upper epidermis so that they can block or absorb ultraviolet rays. However, some topical prescription and nonprescription medications are designed to pass through the epidermis and enter the circulatory capillaries that lie just beneath. This property is called transcutaneous absorption. TRANSCUTANEOUS ABSORPTION Molecular size, chemical properties, and the specific chemical mixture influence the efficiency of transcutaneous absorption. Small molecules move through the layers of the skin more easily than large ones, just as some chemical properties allow substances to pass into and through the skin's lipid layer more easily than others. Transcutaneous absorption is also assisted by particular mixtures of chemicals (as seen in essential oils), as well as the presence of special enhancer chemicals. Skin characteristics products are designed to be absorbed by the primary user, we have to wonder whether massage therapists could absorb them as well. also influence the efficiency of absorption. Areas with many hair follicles allow more passageways for substances to penetrate into skin and access the blood vessels. Areas where the skin is relatively thin allow for greater absorption compared to thick skin. Compromised skin—as seen with the pathologically dry skin of eczema, ichthyosis, and psoriasis—is also more easily penetrated by chemical compounds because the epidermis lacks the sealant qualities found in healthy skin. TOPICAL APPLICATIONS Manufacturers make gels, lotions, patches, and sprays that enhance transcutaneous absorption. The appeal of these is threefold: increased convenience, fewer side effects, and improved compliance. Some amount of medication is absorbed through the skin and directly into the bloodstream, thus bypassing the liver and gastrointestinal system. This decreases Visit the newly designed Log in. Explore. Enjoy. 49

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