Homy layer

Colorimetric, spectrophotometric and histochemical studies have shown that the homy layer is the epidermal barrier to nickel absorption [270]. The carboxyl groups of the keratin have been found to be important in the binding of nickel [271, 272],... 

The homy layer consists of about 10% extracellular components such as lipids, proteins, and mucopolysaccharides. Around 5% of the protein and lipids form the cell wall. The majority of the remainder is present in the highly organized cell contents, predominantly as keratin fibers, which are generally assigned an a-helical structure. They are embedded in a sulphur-rich amorphous matrix, enclosed by lipids that probably he perpendicular to the protein axis. Since the stratum comeum is able to take up considerably more water than the amount that corresponds to its volume, it is assumed that this absorbed fluid volume is mainly located in the region of these keratin structures. 

Malten KE, Spruit D, Boemaars HGM, et al. 1968. Homy layer injury by solvents. Bemfsdermatosen 16 135-147. 

Liposome-encapsulated tretinoin has been tested in hairless mice as well as in man. The animal experiment has demonstrated the favorable uptake of the retinoid, whereas the liposomal lipids appear to be more retained in the homy layer [53], Moreover, with phospholipid-based liposomes belonging to the gel-state type, tretinoin penetration in murine skin appears to be confined to the epidermis [54] and, thus, is close to prednicarbate penetration described above. In patients with acne vulgaris, we could demonstrate a better tolerability of liposomal tretinoin as compared to a commercial gel while efficiency remains the same [55],... 

The skin barrier properties and effect of hand hygiene practices are known to be important in protecting the body. The average adult has a skin area of about 1.75 m2. The superficial part of the skin, the epidermis, has five layers. The stratum corneum, the outermost layer, is composed of flattened dead cells (comeocytes or squames) attached to each other to form a tough, homy layer of keratin mixed with several lipids, which help maintain the hydration, pliability, and barrier effectiveness of the skin. This part of skin has been compared to a wall of bricks (comeocytes) and mortar (lipids) and serves as the primary protective barrier. Approximately 15 layers make up the stratum corneum, which is completely replaced every 2 weeks a new layer is formed almost daily. From healthy skin, approximately 107 particles are disseminated into the air each day, and 10% of these skin squames contain viable bacteria. This is a source of major dirt inside the house and contributes to many interactions. 

Bettinger, J., Gloor, M., Peter, C. et al. Opposing effects of glycerol on the protective function of the homy layer against irritants and on the penetration of hexyl nicotinate. Dermatology 1998, 197 18-24. 

Weigmann, H.J., Lademann, J., Meffert, H., Schaefer, H., and Sterry, W., Determination of the homy layer profile by tape stripping in combination with optical spectroscopy in the visible range as a prerequisite to quantify percutaneous absorption. Skin Pharmacol. Appl. Skin. Physiol. 12, 1999, 34-45. 

Sodium lauryl sulfate (SLS) test6 — The SLS attacks the horny layer, making it more penetrable to chemicals and also causing inflammation. Thus, it measures both the homy layer barrier and tissue reactivity to toxic substances. Aluminum chambers are filled with 0.1 ml of 1 and 2.5% aqueous solutions of SLS. The chambers are then applied to the ventral forearm for 24 h. The reactions are scored 3 h after removal of the chambers on a scale. Those reacting strongly to the lower concentration of SLS are deemed more reactive or sensitive. 

Cutaneous exposure may be selected to simulate the main route of human exposure and as a model for induction of skin lesions. During skin absorption, the chemical applied is transferred from the outer surface of the skin through the homy layer, the epidermis, the comeum, and into the systemic circulation. Absorption of chemicals through the skin is time-dependent, and this can be demonstrated by the application of occlusive bandages to prevent loss of the test material from the application site. Solid chemicals and chemicals soluble in secretions of the skin may dissolve in the secretions to a variable extent. 

Swanbeck, G. and Thyresson, N. (1962). A study of the state of aggregation of the lipids in normal and psoriatic homy layer. Acta Dermato-Venereologica 42 445. 

Montes, L. F. et al. Ultrastructural changes in the homy layer following local application of dimethyl sulfoxide to guinea pig skin. Journal of Investigative Dermatology 48(2) MA 96, 1967. 

Gloor, M. el al. Water content of the homy layer and skin surface lipids. Archives of Dermatological Research 268 121-123, 1980. 

Gloor, M., Hirsh, G. and Willebrandt, U. On the use of infrared spectroscopy for the in vivo measurement of the water content in the homy layer after application of dermatological ointments. Archives of Dermatological Research 271 305-314, 1981. 

Tretinoin is usually applied as a 0.05% polyethylene glycol (PEG)-400/ethanol liquid or a 0.05% hydrophilic cream. Daily application results in inflammation, erythema, and peeling of the skin. After 3 to 4 weeks. pu.stular eruptions may be seen, causing the expulsion of microcomedones. Treatment may then be changed to applications every 2 or 3 day.s. Because the homy layer is thinned, the skin is mote susceptible to irritation by chemical or physical abuse. Thus, it is recommended that other kerolytic agents (.salicylic, sulfur, resorcinol, benxoyl peroxide) be discontinued before beginning treatment with tretinoin. 

Epstein and Maibach carefully defined renewal time of the viable epidermis as the average time needed for all basal cells to reach the homy layer. On the other hand, transit time is defined as the time needed for a basal cell to reach the granular layer. Actually what was meant by transit time was the appearance of the first labeled cells at the granular layer, and this is the minimum transit time although this was not explicitly stated. As the authors pointed out if all cells move at the same rate, transit time will equal renewal time. Otherwise, transit time will always be less than the renewal time. The results of their study were as follows. 

H22. Hodgson, C. M. B., Nucleic acids and their decomposition products in normal and pathological homy layers. J. Invest. Dermatol. 89, 69-79 (1962). 

Lustig, B., Katchem, B., and Reiss, R., The amino acid composition of the homy layer of the human skin. J. Invest. Dermatol. 30, 159 (1958). 

Gender too affects the appearance of human skin. Nevertheless, there is little evidence that the skins of male and female differ greatly in permeability. However, there are established differences in the barrier properties of skin across the races of humans. While the homy layers of Caucasians and Blacks are of equal thickness, the latter population has more cell layers and is measurably denser (30). As a consequence, black skin tends to be severalfold less permeable (30,31). 

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