Skin penetration

As well as the direct influence of the emulsion type and structure on skin penetration, attention has recently been focused on effects which are associated with changes in the emulsion structure after topical application. When emulsions are applied to the skin, they are spread out over it in the form of a thin film. The emulsions heat up to skin temperature, and components with a high vapor pressure begin to evaporate. Drying experiments on thin emulsion films show that— depending on atmospheric humidity and layer thickness—almost all of the water escapes from the emulsion within 5 to 10 minutes. In this window of time there is a change in the viscosity behavior of the emulsion, and in some cases also in its structure. Such phase changes may have dramatic effects on the thermodynamic 

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For a rough estimation of the optimum excitation frequency for a given test object, one can use the well known expression for the skin penetration depth S ... 

Dermal Toxicity. Fatty alkylamines are not considered especially toxic with regard to skin penetration and systemic absorption into the body certain polyamines may be absorbed through the skin to a much greater degree. The acute dermal LD q of decylamine in rabbits has been reported to be... 

The effect of acid stmcture on skin penetration and skin irritation has been studied (57). 

The primary routes of entry for animal exposure to chromium compounds are inhalation, ingestion, and, for hexavalent compounds, skin penetration. This last route is more important in industrial exposures. Most hexavalent chromium compounds are readily absorbed, are more soluble than trivalent chromium in the pH range 5 to 7, and react with cell membranes. Although hexavalent compounds are more toxic than those of Cr(III), an overexposure to compounds of either oxidation state may lead to inflammation and irritation of the eyes, skin, and the mucous membranes associated with the respiratory and gastrointestinal tracts. Skin ulcers and perforations of nasal septa have been observed in some industrial workers after prolonged exposure to certain hexavalent chromium compounds (108—110), ie, to chromic acid mist or sodium and potassium dichromate. 

Grandjean, P. (1990) Skin Penetration, Hazardous Chemicals at Work, Taylor and Francis, London. 

DDT enters an insect by dissolving the thin layer of fatty substances that repel water from the creature s waxy outer skin. Penetrating the layer, DDT reaches the insect s nerve endings and gradually paralyzes vital nerve centers. After a short period of extraordinary excitement, insects sprayed with DDT become progressively paralyzed, fall on their backs, and die. Later, it was learned that DDT allows sodium ions to enter insect tissue through voltage-sensitive channels and make the nerves fire uncontrollably. Because animals and people absorb much less sodium in their tissues, DDT is selectively toxic to insects. 

In addition, the use of biological monitoring has the advantage that skin penetration under particular conditions of protective clothing is included as well in the approach. The results of a dose-excretion study of propoxur by Meuling et al. (1991) using volunteers indicate a significant increase of the dermal uptake of the compound under conditions of occlusion, where there is increased blood flow, skin temperature, and skin moisture. 

Pharmaceutical Skin Penetration Enhancement, edited by Kenneth A. Walters and Jonathan Hadgraft... 

Bennat, C. and Miiller-Goymann, C.C. (2000) Skin penetration and stabilizationof formulations containing microfine titanium dioxide as physical UV filter. International Journal of Cosmetic Science, 22 (4), 271-283. 

Izquierdo, P., Wiechers, J.W., Escribano, E., Garcia-Celma, M.J., Tadros, T.F., Esquena, J., Federen, J.C. and Solans, C. (2007) A study on the influence of emulsion droplet size on the skin penetration of tetracaine. Skin Pharmacology and Physiology, 20, 263—270. 

Sukhdeo et al. (1997) presented an analysis of the phylogeny of strongylid nematodes which they claim demonstrated that the ancestral nematode was a skin-penetrating tissue migrator, and that one clade of parasites (the Trichostrongylidae and Heligmosomidae) has secondarily... 

Abraham, M. H., Chadha, H. S., Mitchell, R. C., The factors that influence skin penetration of solutes,... 

Matousek J. Protective properties of standard combat clothing against skin penetration of supertoxic lethal chemical warfare agents. In Sohns T., Voicu V. A. (Eds.) NBC Risks Current Capabilities and Future Perspectives for Protection. Kluwe Academic Publishers, Dordrecht - Boston - London, 1999, pp 303-310. 

In the case of nonrelativistic laser intensity, linear theory does not allow propagation in overdense plasmas, namely when to 1 < iop(. = e(An/rn,.) 2n,J 2. In the extreme case of ultra-relativistic laser intensity (ao 2> 1), the cutoff frequency for propagation drops from u pe down to wpe/(l Tag)1/4 [11], where ao = eA/mec is the dimensionless amplitude of the laser field. Then, in order for the propagation to occur at plasma density appreciably higher than the ordinary critical density, ao 2> 1 is needed. This is also the case of overdense thin plasma layers (as proved by simulation [12]) whose thickness exceeds the skin penetration depth of the e.m. wave. Theoretical background and basic... 

Fisher and Hall reported the propionate salt to be unsuitable for use in ophthalmic preparations33. Other salts described in the literature are neomycin glucuronate43, succinate43 44, lactate45, ascorbate45, phthalate44and the sulphosuccinate4 4 which has the property of improved skin penetration. 

If the substances have passed the stratum comeum, they also generally diffuse into the living part of the epidermis, reach the circulation, and then have systemic effects depending on the amount absorbed. Because these are often constituents of formulations, one generally expects them to have little direct influence on skin penetration. However, their amphiphilic properties allow them to form new systems with the body s constituents and even to change the physical state of water in the skin. By this means, a pathway is cleared for other hydrophilic substances to gain entry into the general circulation. 

Scheuplein, R.J. (1967). Mechanism of percutaneous absorption, (ii) Transient diffusion and the relative importance of various routes of skin penetration. J. Invest. Derm. 48 79-88. 

Holland, J., Kao, M. and Whitaker, M.J. (1984). A multisample apparatus for kinetic evaluation of skin penetration in vitro The influence and metabolic status of the skin. Toxicol. Appl. Pharmacol. 72 272-280. 

Commercial interest in CNTs has led to the development of mass production and handling facilities. Risks of exposure by various routes need to be clarified because CNTs may penetrate the body through the skin as well as the lung and gut (Donaldson et al., 2006). Even if our understanding of local, chronic, and metabolic toxicity through the skin penetration is not clear, there is a broad consensus that CNTs can enter through the skin and distribute throughout the body (Nohynek et al., 2007 Tsuji et al., 2006). 

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