Stratum corneum penetration

It is a lipophilic compound which removes intercellular lipids that are covalently linked to the cornified envelope surrounding epithelial cells [3]. It also enhances penetration of other agents. Resorcinol (m-dihydroxy benzene) is structurally and chemically similar to phenol. It disrupts the weak hydrogen bonds of keratin [4]. Lactic acid is an alpha hydroxy acid which causes corneocyte detachment and subsequent desquamation of the stratum corneum [5]. 

Salicylic acid (ortho hydroxybenzoic add) is a beta hydroxy acid agent. It is a lipophilic compound which produces desquamation of the stratum corneum via removal of intercellular lipids [3] (see salicylic acid section). Given its keratolytic effects, it has become an increasingly popular superficial peeling agent. Salicylic acid peels induce injury via thinning or removal of the stratum corneum. In addition, salicylic acid potentially enhances the penetration of TCA. 

In addition, data obtained from infrared, thermal, and fluorescence spectroscopic studies of the outermost layer of skin, stratum corneum (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 (for a recent review, see Ref. 206). 

Since dermatophyte hyphae seldom penetrate into the living layers of the skin, instead remaining in the stratum corneum, most infections can be treated with topical antifungals. Infections... 

Fungal skin infections are primarily caused by dermatophytes such as Trichophyton, Microsporum, and Epidermophyton. Trichophyton rubrum accounts for more than 75% of all cases in the United States.36 To a lesser extent, Candida and other fungal species cause skin infections. With tinea infections, the causative dermatophyte typically invades the stratum corneum without penetration into the living tissues, leading to a localized infection. 

Since dermatophyte hyphae seldom penetrate into the living layers of the skin, instead remaining in the stratum corneum, most infections can be treated with topical antifungals. Infections covering large areas of the body or infections involving nails or hair may require systemic therapy. Patients with chronic infections or infections that do not respond to topical therapy are also candidates for systemic therapy. 

Use of topical retinoids (tretinoin, tazaro-tene, retinol formulations) for 2 to 6 weeks prior to peeling thins the stratum corneum, reduces the content of epidermal melanin, and expedites epidermal healing. Retinoids also enhance the penetration of the peeling agent. They should be discontinued several days prior to the peeling procedure. Retinoids can be resumed post-operatively after all evidence of... 

Skin toxicity is determined by the penetration and transport of the compound being tested through the lipid matrix in the outer skin layers (the stratum corneum)... 

Under normal conditions, the transcellular route is not considered as the preferred way of dermal invasion, the reason being the very low permeability through the corneocytes and the obligation to partition several times from the more hydrophilic corneocytes into the lipid intercellular layers in the stratum corneum and vice versa. The transcellular pathway can gain in importance when a penetration enhancer is used, for example, urea, which increases the permeability of the corneocytes by altering the keratin structure. 

Pugh WJ, Degim IT, Hadgraft J (1996) Epidermal permeability-penetrant structure relationships 4. QSAR of permeant diffusion across human stratum corneum in terms of molecular weight, H-bonding and electronic charge. Int J Pharm 197 203-211. 

The skin immune system is challenged everyday with an enormous variety of potential sensitizers which penetrate the stratum corneum and trigger the two major populations of dendritic cells (DCs)... 

Not surprisingly damage to the skin enhances absorption rates if the less protective dermis is exposed because the stratum corneum has been scraped off, penetration can be substantial. 

Log Po/ For substances with values below 0, poor Upophilicity will limit penetration into the stratum corneum... 

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