Hair lipids transport

When an electric potential is imposed across the skin, as in iontophoresis, ions will move along the pathways of lowest electrical resistance. Although the exact anatomical location of these low-resistance shunt pathways has not been well characterized, recent microscopy studies have shed mechanistic insight on the problem. Experimental variables of particular importance that have been shown to strongly influence the preferred iontophoretic transport pathways include (a) the physicochemical nature of the penetrant and (b) the penetrant s affinity for the different environments available (e.g., hair follicle, sweat duct, intercellular lipids). These unresolved and, in some cases, controversial issues will be discussed in the context of both classical and recent microscopy investigations. 

The composition of the lipid itself may influence its transport because ingredients that either lower the surface tension of the sebum or increase its fluid nature (make it less viscous) can facilitate transport and even increase the perception of oiliness. In addition, other ingredients left behind on the hair surface (e.g., conditioning agents) may exacerbate oiliness in an analogous manner. 

A chemical s transport from the environment to a biological active site can follow any of several alternate pathways, or side routes. If the molecule happens to reach a metabolicahy active tissue, such as a neuron or a liver cell, it may do substantial harm. If, however, the toxic compound entering the body can be misdirected or sequestered into a relatively inactive tissue, such as bone or adipose tissue, then the toxic compound may not reach receptor sites in more meta-bolicaUy active tissues, at least not in the quantity necessary to elicit an immediate toxic impact. Metal ions sequestering into bone or hair and lipid-soluble compounds such as DDT sequestering into fat are two classic examples of such containment. 

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