Epidermis phenol effects

The cause of phenol s corrosive properties does not relate to its ability to form solvated protons (as indicated by the value of Ka) but its ability to penetrate the skin and disrupt the chemical processes occurring within the epidermis, to painful effect. 

The fact that in most cases they cannot use camouflage make-up makes it difticult to carry out a local or full phenol peel. Moreover, phenol peels produce less spectacular results on thick skins than on thin skins. Shaving does not pose a problem, as a peel to the basal layer of the epidermis does not rule out shaving, even with a blade. For a peel to the papillary or reticular dermis, it is best not to shave while the skin is flaking. It is usually possible to shave after the 8th day. Alcohol-based aftershaves should be avoided, and a hydrating, anti-oxidant or firming cream should be used instead, followed by effective sun protection. 

With EMLA, liposoluble anesthetic molecules penetrate the stratum comeum and the rest of the epidermal barrier and soon reach the skin nerve endings. The phenol, which is also liposoluble, can get through the epidermis more quickly. On the surface the shorter contact time between the epidermis and the phenol could reduce epidermal liquefaction. Deep down, a higher concentration of phenol in the reticular dermis could cause the formation of retractile scar tissue. The concentration gradient created in the perivascular spaces of the dermis speeds up the absorption of phenol. The risk of systemic toxicity can also increase. EMLA causes vasoconstriction followed by vasodilation. Vasodilation can sometimes be seen after only 30 minutes of EMLA under occlusion. How will these vasomotor changes affect the effectiveness or absorption of phenol - and therefore its toxicity ... 

In the realm of mechanical damage and in vitro human skin studies, Akomeah et al. [117] and Bronaugh and Stewart [113] examined the effects of tape stripping and abrasion on human abdominal epidermis and found that caffeine, tri-tiated water, acyclovir, urea, and nicotinic acid (Koct -2.12 to 1) permeation was greater than that observed for more lipophilic substances, i.e., benzoic acid, cortisone, phenol, methylparaben, and butylparaben (Koet 1.5-3.6) (Table 4.14). 

The usual classification of chemical peels comprises superficial, medium and deep peels. For superficial peels, AHA, Jessner s solution, tretinoin, TCA in concentrations of 10-30% and most recently hpo-hydroxy add are used to induce an exfoliation of the epidermis. Medium-depth agents such as TCA (30-50%) cause an epidermal to papillary dermal peel with subsequent regeneration. Deep peels using TCA (>50%) or phenol-based formulations penetrate the reticular dermis to induce dermal regeneration. The success of peeling in darker skin is crudally dependent on the physician s understanding of the chemical and biological processes, as well as of indications, clinical effectiveness and side effects of the procedure (see Box 9.1). 

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