Ethanol effects on the stratum corneum lipid phase behavior

Implications of surfactant hydrophobic chain architecture on the Surfactant-Skin lipid model interaction

Although surfactants have been widely used in skin care and other related applications, our knowledge about how surfactants interact with stratum corneum (SC) lipids remains limited. This work reports how surfactants interact with a lipid SC model by neutron diffraction and molecular dynamics (MD) simulations, focusing on examining the impact of surfactant molecular architecture. The surfactant-SC mixed membrane was constructed by an equimolar mixture of ceramide/cholesterol/fatty acids and surfactant at 1% molar ratio of total lipids. The arrangements of water and surfactant molecules in the membrane were obtained through neutron scattering length density (NSLD) profiles via contrast variation method, meanwhile, MD simulation clearly demonstrated the mechanism of hydration change in the surfactant-model SC mixed membrane. No drastic difference was detected in the repeating distance of the short periodicity phase (SPP) upon adding surfactants, however, it significantly enhanced the membrane hydration and reduced the amount of phase separated crystalline cholesterol, showing a strong dependence on surfactant chain length, branching and double bond. This work clearly demonstrates how surfactant architecture affects its interaction with the SC membrane, providing useful guidance for either choosing an existing surfactant or designing a new one for surfactant-based transdermal application.

Central composite design for the development of carvedilol-loaded transdermal ethosomal hydrogel for extended and enhanced anti-hypertensive effect

Background

Carvedilol, the anti-hypertensive drug, has poor bioavailability when administered orally. Ethosomes-mediated transdermal delivery is considered a potential route of administration to increase the bioavailability of carvedilol. The central composite design could be used as a tool to optimize ethosomal formulation. Thus, this study aims to optimize carvedilol-loaded ethosomes using central composite design, followed by incorporation of synthesized ethosomes into hydrogels for transdermal delivery of carvedilol.

Results

The optimized carvedilol-loaded ethosomes were spherical in shape. The optimized ethosomes had mean particle size of 130 ± 1.72 nm, entrapment efficiency of 99.12 ± 2.96%, cumulative drug release of 97.89 ± 3.7%, zeta potential of − 31 ± 1.8 mV, and polydispersity index of 0.230 ± 0.03. The in-vitro drug release showed sustained release of carvedilol from ethosomes and ethosomal hydrogel. Compared to free carvedilol-loaded hydrogel, the ethosomal gel showed increased penetration of carvedilol through the skin. Moreover, ethosomal hydrogels showed a gradual reduction in blood pressure for 24 h in rats.

Conclusions

Taken together, central composite design can be used for successful optimization of carvedilol-loaded ethosomes formulation, which can serve as the promising transdermal delivery system for carvedilol. Moreover the carvedilol-loaded ethosomal gel can extend the anti-hypertensive effect of carvedilol for a longer time, as compared to free carvedilol, suggesting its therapeutic potential in future clinics.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-00833-4.

Molecular mechanism of the skin permeation enhancing effect of ethanol: a molecular dynamics study

Ethanol is widely used in various pharmaceutical and cosmetic formulations in order to enhance skin penetration of active ingredients. While it is well known that ethanol partitions into the skin and enhances the permeation of both polar and nonpolar molecules, the exact mechanisms by which it enhances skin permeability are not fully understood. Several mechanisms have been proposed including lipid extraction from the stratum corneum (SC), fluidisation of SC lipid bilayer, alteration of SC protein conformation and enhancement of the drug solubility in the SC lipids. In this study, we performed molecular dynamics (MD) simulations of SC lipid bilayers comprised of an equimolar mixture of ceramides, cholesterol and free fatty acid in the presence of aqueous mixtures of ethanol. Various unrestrained MD simulations were performed in the presence of aqueous ethanol solution at molar ratios (x) ranging from x = 0 to x = 1. It was found that ethanol enhances bilayer permeability by dual actions (a) extraction of the skin lipids and (b) enhancing the mobility of lipid chains. Ethanol's permeation enhancing effect arises from its superior ability to form hydrogen bonds with headgroup atoms of skin lipids. Further, the free energy of extraction of ceramides (CER) and fatty acids (FFA) from the lipid bilayer was studied using umbrella sampling simulations. The free energy of extraction of CER was found to be much higher compared to FFA for all ethanol concentrations which shows that CER are difficult to extract as compared to FFA. Finally, the permeation of benzoic acid drug molecules through the skin lipid bilayer is shown in presence of ethanol molecules. It was found that ethanol selectively targets the FFA of the skin lipid bilayer and extracts it out of the lipid bilayer within few microseconds. Further, ethanol penetrates inside the lipid layer and creates the channels from which drug molecules can easily cross the lipid layer. Our observations (both in unrestrained and umbrella sampling simulations) are consistent with the experimental findings reported in the literature. The simulation methodology could be used for design and testing of permeation enhancers (acting on skin SC lipid lamella) for topical and transdermal drug delivery applications.

Concentration dependent action of mechanism of ethanol on skin SC lipid barrier.

Effect of DMSO, urea and ethanol on hydration of stratum corneum model membrane based on short-chain length ceramide [AP]

Hydration of oriented multilamellar membrane based on ceramide [AP] in the DMSO, urea and ethanol aqueous solutions at various solute concentrations was investigated by neutron diffraction. Neither urea nor DMSO influence the repeat distance of the membrane and internal structure of bilayer at their mole concentration of up to 0.15 and 0.10, respectively. The d-spacing reduction effect of both compounds was observed at their concentrations of 0.2 for urea and 0.2 and 0.4 for DMSO. Compared to hydration in the pure water, both urea and DMSO slow down the swelling process, and this slowdown is more pronounced with increasing in their concentration. At concentration of 0.2, urea and DMSO induce the slight phase separation of the fully hydrated samples; at the highest used concentration of 0.6, DMSO induces the strong time-depend separation of the sample probably due to fluidization of lipid bilayers. Ethanol at a used molar concentration of 0.03 leads to dissolution of the sample.

Transdermal delivery of raloxifene HCl via ethosomal system: Formulation, advanced characterizations and pharmacokinetic evaluation

Raloxifene HCl belongs to a class of selective estrogen receptor modulators (SERMs) which is used for the management of breast cancer. The major problem reported with raloxifene is its poor bioavailability which is only up to 2%. The main objective of the present work was to formulate raloxifene loaded ethosomal preparation for transdermal application and compare it with an oral formulation of the drug. Five ethosomal formulations with different concentrations of ethanol and a conventional liposomes formulation were prepared by rotary evaporation method. The prepared systems were characterised by high resolution transmission electron microscopy (HRTEM), force emission electron microscopy (FESEM), atomic force microscopy (AFM), X-ray diffraction (XRD) and ³¹P NMR study. All these advanced characterization study established that the ethosome formulation was well defined by its size, shape and its bilayer formation. Transdermal flux of the optimized ethosome formulation was 22.14 ± 0.83 µg/ml/cm² which was 21 times higher when compared to the conventional liposomes. Confocal microscopy study revealed an enhanced permeation of coumarin-6 dye loaded ethosomes to much deeper layers of skin when compared with conventional liposomes. The gel was found to be pseudoplastic with elastic behaviour. In-vivo studies on rats showed a higher bioavailability of RXL (157% times) for ethosomal formulation when compared with the oral formulation. In conclusion, RXL loaded ethosomal formulation via transdermal route showed superior drug delivery properties as compared to oral formulation.

Ethanol induces the formation of water-permeable defects in model bilayers of skin lipids

We observe that ethanol can induce the formation of water-permeable defects in model bilayers of skin lipids and propose this as a new mechanism of action of ethanol as a membrane modulator.

Structure Enhancement Relationship of Chemical Penetration Enhancers in Drug Transport across the Stratum Corneum

The stratum corneum is a major barrier of drug penetration across the skin in transdermal delivery. For effective transdermal drug delivery, skin penetration enhancers are used to overcome this barrier. In the past decades, a number of research studies were conducted to understand the mechanisms of skin penetration enhancers and to develop a structure enhancement relationship. Such understanding allows effective prediction of the effects of skin penetration enhancers, assists topical and transdermal formulation development, and avoids extensive enhancer screening in the transdermal delivery industry. In the past two decades, several hypotheses on chemical enhancer-induced penetration enhancement for transport across the skin lipoidal pathway have been examined based on a systematic approach. Particularly, a hypothesis that skin penetration enhancement is directly related to the concentration of the enhancers in the stratum corneum lipid domain was examined. A direct relationship between skin penetration enhancer potency (based on enhancer aqueous concentration in the diffusion cell chamber) and enhancer n-octanol-water partition coefficient was also established. The nature of the microenvironment of the enhancer site of action in the stratum corneum lipid domain was found to be mimicked by n-octanol. The present paper reviews the work related to these hypotheses and the relationships between skin penetration enhancement and enhancer concentration in the drug delivery media and stratum corneum lipids.

Percutaneous penetration modifiers and formulation effects: thermal and spectral analyses

The study investigated the formulation effects of laurocapram and iminosulfurane derived penetration modifiers on human stratum corneum using thermal and spectral analyses. Firstly, formulations of penetration modifiers were assessed as enhancers/retardants using the model permeant, diethyl-m-toluamide followed by investigation of their mechanisms of action using differential scanning calorimetry (DSC) and attenuated total reflectance Fourier-transform infra-red spectroscopy. The penetration modifiers investigated were laurocapram, 3-dodecanoyloxazolidin-2-one (N-0915), S,S-dimethyl-N-(4-bromobenzoyl) iminosulfurane (DMBIS), S,S-dimethyl-N-(2-methoxycarbonylbenzenesulfonyl) iminosulfurane (DMMCBI) and tert-butyl 1-dodecyl-2-oxoazepan-3-yl-carbamate (TBDOC) that were formulated in either water, propylene glycol (PG), ethanol or polyethylene glycol 400 (PEG 400). The results explain the mechanism for the first time why an enhancer can become a retardant or vice versa depending upon the vehicle in which it is applied to the skin. DSC indicated that penetration modifier formulations enhanced permeation of active mainly by disruption and fluidization of the stratum corneum lipid bilayers while IR data indicated characteristic blue shifts with decreases in peak intensity. On the other hand, DSC of penetration modifier formulations showing retardation depicted elevated T (m2) with a strengthening of lipid-protein complex while IR results indicated formation of multiple peaks around 1,738 cm(-1) transition in stratum corneum spectra suggesting retardation may be caused by organization of SC lipids by increased H-bonding.

Transdermal absorption of the herbicide 2,4-dichlorophenoxyacetic acid is enhanced by both ethanol consumption and sunscreen application

Xenobiotics absorption is a health concern and skin is a major exposure site for many of these chemicals. Both alcohol consumption and topical sunscreen application act as transdermal penetration enhancers for model xenobiotics. The effect of combining these two treatments on transdermal absorption of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) was therefore examined. Skin from rats ingesting low (1.5 g/kg) medium (4.3 g/kg) or high (6 g/kg) ethanol doses or saline control was treated with a commercially available sunscreen containing titanium dioxide and octyl methoxycinnimate and transdermal absorption of 2,4-D was monitored. Ethanol increased penetration by a factor of 1.9, 2.0 and 2.5 for animals treated with 1.5, 4.3 and 6 g/kg respectively, demonstrating an ethanol-induced dose response. Sunscreen application to skin from ethanol gavaged rats caused 2,4-D absorption above that induced by ethanol alone by an additional factor of 1.3, 2.1 and 2.9 for 1.5, 4.3 and 6 g/kg respectively. Comparing 2,4-D transdermal absorption after exposure to both ethanol and sunscreen with a theoretical value (sum of penetration after ethanol or sunscreen treatment) demonstrates that these two treatments enhance additively at the higher doses tested. Results of this study emphasize the importance of limiting excessive alcohol consumption in individuals with potential herbicide exposure rather than discouraging the use of sunscreens, since the consequences of UV-induced skin cancer are far more series than the risks that would be associated with observed increases in chemical exposure.

A Single Oral Dose of Ethanol Can Alter Transdermal Absorption of Topically Applied Chemicals in Rats

Topical ethanol is used as a dermal penetration enhancer in some commercial products. Previous studies have demonstrated that chronic ethanol consumption can also disrupt skin barrier function, leading to increased transdermal penetration. This observation becomes much more relevant if a single drinking episode induces similar changes. The purpose of this study was thus to examine the transdermal penetration of three model chemicals after acute ethanol consumption. Wistar rats were gavaged with either 10, 6, 4.3, 3, 1.5 g/kg ethanol or saline and allowed to recover for 2 or 24 h. Blood and skin ethanol levels were determined and in vitro penetration experiments performed. The herbicide paraquat, industrial solvent N,N-dimethylformamide (DMF), and insect repellent N,N-diethyl-m-toluamide (DEET) were used as is model chemicals. Absorption was determined and directly compared between ethanol- and saline-treated skin by calculating enhancement ratios. Blood ethanol levels range from 0.25 to 0.015% at 2 h with skin levels at 12-18% of blood values. Ethanol enhances the absorption of paraquat, DMF, and DEET in a dose-dependent fashion. Paraquat and DEET showed no appreciable reduction in enhancement between 2 and 24 h postgavage for the 10-g/kg dose, but DMF did. Enhancement ratios were higher at 24 h for 10 than for 6 g/kg animals, demonstrating a dose-response relationship for recovery time. These studies imply that increased absorption of topical chemical occurs after alcohol ingestion. Both acute and chronic ethanol consumption can compromise the dermal barrier.

Feasibility studies of dermal delivery of paclitaxel with binary combinations of ethanol and isopropyl myristate: role of solubility, partitioning and lipid bilayer perturbation

In the current investigation, paclitaxel (PCL) delivery into the different layers of skin, vehicle optimization and relationship between vehicle composition and the relative contribution of solubility, partition and diffusion towards drug transport has been outlined. Saturation solubility of PCL was determined in ethanol (EtOH), isopropyl myristate (IPM) and their binary combinations, and partition studies performed to study the probability of skin depot formation. Epidermal and dermal partitioning was carried from PCL saturated vehicles. Skin permeation of PCL was studied using the rat skin. FT-IR has been utilized to study the skin barrier perturbation, and the localization of PCL and isopropyl myristate (IPM) in epidermis. High K(app) value in mineral oil/buffer indicated the tendency of PCL to form a reservoir in skin, and an inverse relationship between PCL solubility in different solvent systems and partitioning into epidermis was found. Maximum K(epidermis) for PCL was observed with IPM, while PCL in EtOH/IPM (1:1) showed high partitioning into dermis. Maximum flux of PCL was observed with EtOH/IPM (1:1). For lipophilic drug like PCL modulation of vehicle seems to be effective approach to increase the permeability across the skin. With a binary combination of EtOH/IPM (1:1) higher concentration of PCL can be delivered to deeper layer of skin whereas with IPM higher concentration of PCL could be localized in the epidermis. While engineering the delivery vehicle selection of solvents should be such that one of them is miscible in both hydrophilic and lipophilic phase like ethanol and another should be lipophilic in nature (IPM in this case) so that an optimum balance between 'push-pull' and 'blending' effect can be achieved.

The porcine snout--an in vitro model for human lips?

The morphology and histology of test sites commonly used to study the penetration of lip products differ significantly from those of the human lip itself. The aim of this study was to investigate whether the porcine snout could serve as an equivalent in vitro model for human lips. The lips of human test subjects and biopsies of porcine snout tissue were compared using histological and microscopic techniques. Using a dermatological laser scanning microscope, the penetration of topically applied fluorescent sodium fluorescein was investigated in vivo on human lips and in vitro on the porcine snout. Biopsies from the in vitro experiments were studied using fluorescence microscopy. Some parts of the porcine snout show a similar morphology and histology as human lips. The stratum corneum (SC) and the epidermis of the porcine snout are thicker than those of human tissue. Both in vivo and in vitro, the topically applied fluorescent dye was detected only on the skin surface and within the uppermost SC layer. These results indicate that porcine snout can be used as an in vitro model for human lips in penetration studies. Both human and porcine tissues exhibit an efficient barrier against the penetration of topically applied substances.

Orally administered ethanol: transepidermal pathways and effects on the human skin barrier

Ethanol intake is associated with a variety of skin diseases. The aim of the present study was (1) to identify the pathways of release of orally administered ethanol through the skin, and (2) to investigate the effects of a single oral dose of ethanol on the penetration of topically applied substances into the skin. Ethanol evaporation via the skin was measured using the new technique of ion mobility spectrometry (IMS). Transepidermal water loss (TEWL) and skin surface temperature were simultaneously measured before and after ethanol consumption. Measurements were performed on skin sites with different stratum corneum (SC) thickness, and density of follicles and sweat glands. These appendages were selectively sealed to investigate their participation in ethanol evaporation. The penetration of a topically applied UV filter substance was studied before and after ethanol consumption after removing the SC with adhesive tape. Ethanol evaporation was measured within 5 min of consumption, while the skin surface temperature remained nearly constant. The sealing of the appendages did not have a significant effect on ethanol evaporation. On the forehead, a higher TEWL value was measured than on the forearm. On both skin sites, an increase in TEWL was observed after ethanol ingestion. No influence of orally administered ethanol on the penetration of the topically applied UV filter substance was observed. The results indicate that ethanol evaporation occurs via the lipid layers without a significant effect on the penetration of the topically applied substance.

Synergistic penetration enhancement effect of ethanol and phospholipids on the topical delivery of cyclosporin A

In the present study, ethanol was used with a commercially available lipid mixture, NAT 8539, to improve the topical delivery of cyclosporin A (CyA). The vesicles formed from this solution ranged from 56.6 to 100.6 nm in diameter, depending on the amount of ethanol added in the formulation. In-vitro skin penetration studies were carried out with Franz diffusion cell using human abdominal skin. There was a decrease in average size of vesicles, as the amount of ethanol in formulation increased from 0% to 3.3% and a further addition of ethanol resulted in an increase in average diameter of vesicles. CyA vesicles containing 10% and 20% ethanol showed statistically enhanced deposition of CyA into the stratum corneum (SC), as compared to vesicles prepared without ethanol. CyA vesicles prepared with NAT 8539/ethanol (10/3.3) showed a 2.1-fold, CyA vesicles with NAT 8539/ethanol (10/10) showed a 4.4-fold, and CyA vesicles with NAT 8539/ethanol (10/20) showed a 2.2-fold higher deposition of CyA into SC, as compared to vesicles made of NAT 8539 without ethanol [NAT 8539/ethanol (10/0)]. The efficiency of the formulations was sequenced in the order of: NAT 8539/ethanol (10/10)>NAT 8539/ethanol (10/20)>NAT 8539/ethanol (10/3.3)>ethanol>NAT 8539/ethanol (10/0). These results can be considered a step forward for the topical delivery of problematic molecules like CyA using liposomes as a tool for the treatment of inflammatory skin diseases like psoriasis, atopic dermatitis, and diseases of the hair follicle like alopecia areata, etc.

Effects of chronic alcohol consumption on dermal penetration of pesticides in rats

Topically applied ethanol is a well-known dermal penetration enhancer. The purpose of this work was to determine if ethanol consumption might also increase transdermal penetration. Male rats were fed either an ethanol containing or control diet for 6-8 wk. After the feeding regime was completed, skin was removed and placed in an in vitro diffusion system. The transdermal absorption of four very commonly used herbicides was determined. Penetration through skin from ethanol-fed rats was enhanced when compared to control by a factor of 5.3 for paraquat, 2.4 for atrazine, and 2.2 for 2,4-dichlorophenoxyacetic acid (2,4-D), and reduced by a factor 0.6 for trifluralin. Comparison of physical factors of the herbicides to the penetration enhancement revealed an inverse linear correlation with lipophilicity, as defined by log octanol/water partition coefficient (log Kow) with r2 =.98. These changes were at least partially reversible after 1 wk of abstinence from ethanol. These experiments demonstrate that regular ethanol consumption can alter the properties of the dermal barrier, leading to increased absorption of some chemicals through rat skin. If ethanol consumption has the same effect on human skin it could potentially have adverse health effects on people regularly exposed to agricultural, environmental, and industrial chemicals.

Effect of the vehicle on the amount of stratum corneum removed by tape stripping

BACKGROUND

The penetration of topically applied substances into the stratum corneum can non-invasively be studied using the tape stripping procedure. This method was applied to investigate in vivo the penetration of a fragrance, vanillin, applied in ethanol and a w/o emulsion.

METHODS

Twenty tape strips were removed from each skin area treated with vanillin in ethanol or w/o emulsion, respectively. The concentration of vanillin was determined for each tape strip. In addition, the pseudo-absorption of the corneocytes was determined to calculate the SC profile.

RESULTS

The vanillin concentration was correlated both with the tape number and with the stratum corneum profile. Depending on whether the tape number or the profile of the stratum corneum were correlated with the vanillin concentration, different distributions within the stratum corneum were obtained. Different amounts of stratum corneum were removed with 20 tape strips dependent on the vehicle applied previously. The application of the w/o emulsion led to the removal of nearly the half the amount of corneocytes stripped from the ethanol-treated area.

CONCLUSIONS

The results obtained underline the general necessity to correlate the amount of stratum corneum with the amount of substance in penetration studies.

Chemical enhancement of percutaneous absorption in relation to stratum corneum structural alterations

The outermost layer of the skin, stratum corneum (SC), provides an outstanding barrier against the external environment and is also responsible for skin impermeability toward most solutes. The barrier function is related to the unique composition of the SC lipids and their complex structural arrangement. The lipoidal matrix of the SC, therefore, is a target of penetration enhancer action. The literature on the skin barrier structure and function and on the mechanisms of action of some well established permeation promoters, with a focus on their impact on SC structural alterations, is reviewed. Data obtained from infrared, thermal, and fluorescence spectroscopic examinations of the SC and its components imply enhancer improved permeation of solutes through the SC is associated with alterations involving the hydrocarbon chains of the SC lipid components. Data obtained from electron microscopy and X-ray diffraction reveals that the disordering of the lamellar packing is also an important mechanism for increased permeation of drugs induced by penetration enhancers.

Effect of penetration enhancers and iontophoresis on the ultrastructure and cholecystokinin-8 permeability through porcine skin

The present study explores the effect of chemical penetration enhancers and iontophoresis on the in vitro permeability of cholecystokinin-8 (CCK-8) through porcine epidermis and on the ultrastructural changes in stratum corneum as observed by transmission electron microscopy (TEM). Enhancer [i.e., ethanol (EtOH), and 10% oleic acid in combination with ethanol (OA/EtOH)] pretreatment significantly increased (p < 0.01) the permeability coefficient of CCK-8 in comparison with the control (pretreated epidermis without enhancer). Iontophoresis further increased the permeability of CCK-8 (p < 0.01) through the enhancer-pretreated epidermis in comparison with the control. These results showed the synergistic effect of iontophoresis and enhancers such as OA/EtOH that provides an additional driving force to maintain and control the target flux of CCK-8. The ultrastructure of stratum corneum treated with ethanol demonstrated a loss of structural components in the superficial stratum corneum cell layers. OA/EtOH transformed the highly compact cells of stratum corneum into a looser network of filaments, creating an increased free volume and greater intracellular surface area. Treatment of stratum corneum with OA/EtOH followed by iontophoresis resulted in further swelling of stratum corneum cell layers. In conclusion, OA/EtOH in combination with iontophoresis increased the permeability of CCK-8 by loosening and swelling of stratum corneum cell layers.

Enhanced permeation of polar compounds through human epidermis. I. Permeability and membrane structural changes in the presence of short chain alcohols

The influence of alcohol chain length on polar compound permeation in human skin was investigated to further understand alcohol-enhanced permeation mechanisms. Both thermodynamic and kinetic variables associated with the enhanced permeation of mannitol were ascertained in the presence of high concentrations of short chain alcohols. Permeation of mannitol through human epidermis in the presence of 75% (v/v) alcohol-saline mixtures was determined in symmetric, side-by-side diffusion cells at 32 degrees C. Permeability coefficients increased with increasing alcohol chain length (iso-propanol > ethanol > methanol). Uptake of mannitol into the epidermal tissue increased in the presence of the short chain alcohols, but was independent of alcohol chain length. In addition, mannitol solubility decreased in the presence of the short chain alcohols, but again was independent of alcohol chain length. Therefore, increased mannitol permeability with increasing alcohol chain length could not be attributed to thermodynamic variables. Changes in the amount and conformation of stratum corneum lipids and proteins were determined by Fourier transform infrared (FTIR) spectroscopy. Stratum corneum lipid conformation and mobility was not significantly altered in the presence of the short chain alcohols. However, decreased absorbance of the alkyl chain suggested lipid extraction, which increased with increasing alcohol chain length. Stratum corneum protein conformation was altered in the presence of the short chain alcohols. Decreased infrared absorbance of the Amide I band maximum suggested extraction of stratum corneum proteins, which increased with increased alcohol chain length. These results suggest a correlation between enhanced permeation and extraction of lipids as well as proteins from human skin in the presence of 75% (v/v) aqueous alcohol solutions.