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| Home > Multi-Lamellar Emulsion (MLE) |
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| To understand the role of our skin, it is better to start from its structure. As shown in Figure 1, our skin consists of three particular layers from the exterior such as epidermis, dermis, and subcutaneous tissue. There are also supplementary organs such as hair, capillary vessels, eccrine gland, and sebaceous gland. The epidermis is the thinnest layer of the three and is responsible for moisturizing and protecting skin. |
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| It also houses keratinocytes and melanocytes. The dermis encompasses collagens and elastins, which are crucial in skin elasticity (wrinkles). It also houses stromata made up of blood vessels, mucopolysaccharides, and nerves, as well as mast cells relating to allergic reactions. The subcutaneous tissue, dubbed hypodermis, consists of fat tissues, which plays a key role in feeding nutrition to the epidermis and dermis, determining the bodily form, and maintaining the body temperature among others. As shown in Figure 2, the epidermis consists of the stratum basale, stratum spinosum, stratum granulosum, and stratum corneum. The stratum basale is responsible for the cell differentiation of keratinocytes called keratinization. The differentiated cells gradually climb up as they pass through the stratum spinous and granulosum, then, eventually become keratinocytes thus forming the stratum corneum. |
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| Keratinized cell layers, namely strata corneum, are detached from skin in a certain time, giving way to newly created strata corneum. This repeated process is referred to as “rejuvenation,” and the cycle takes place about every 4-6 weeks(about 28 days). Thus, our skin can stay in supple and soft state through the rejuvenation. |
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| We can say that the physiochemical and biological functions of the most skincare products of the past decades were generally concerned with the stratum corneum (SC). Elias from UCSF proposed the structure of the SC in an illustration as 'the brick & mortar model' in 1981. The brick represented corneocyte and the mortar represented intercellular lipid composed of cholesterol, fatty acid, and ceramide. The corneocyte is filled with keratin and embedded in the inter-corneocyte lipid, which forms lamellar structure. The purpose of the brick & mortar structure is believed to give our skin elasticity and suppleness, plus the protection called the skin barrier function. |
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| The skin barrier can be removed by melting lipid layers with an organic solvent or detergent. After the disruption, a homeostatic repair response begins within the epidermis, which results in the restoration of the barrier function. This repair process includes (1) the exocytosis of lamellar body contents from stratum granulosum cells, (2) the increased synthesis of epidermal cholesterol, fatty acid, and sphingolipid, (3) the accelerated formation and secretion of nascent lamellar body, (4) the extracellular processing of polar lipid to their more non-polar product, and (5) the increase in epidermal DNA synthesis. These metabolic alterations in the epidermis result in the replenishment of the lipid in the SC and to the normalized barrier function. |
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| The main components of intercellular lipids are ceramide, fatty acid, and cholesterol. And the ceramide is supposed to be not only the most prominent substance of lipids found in SC but also the important components for the formation and retention of lamellar structure in SC. |
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| The stratum corneum (SC) is an exterior layer of our skin that is in direct contact with the external environment, making it the crucial part of the human body. Damage to the SC can become a direct cause of various skin troubles and skin diseases. To keep the skin healthy, a better understanding of the stratum corneum and awareness of the skincare are required. |
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| (i) Keratinocytes and Lipids between Keratinocytes |
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| The stratum corneum basically consists of keratinocytes and lipids in between, as well as epidermal lipids and natural moisturizing factors (NMF). A keratinocyte is a cell that is keratinized from the stratum basale of the epidermis and filled with protein dubbed keratin. It provides waterproof function to the epidermis. A keratinocyte is one kind of the dead skin cells. The lipids between keratinocytes fill the area between keratinocytes and have a lamellar liquid crystalline structure, and function to soften, moisturize, and protect the skin. |
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| This unique structure of bricks and mortar type enables the skin barrier function. The function prevents the intrusion of surface impurities and the loss of internal moisture, electrolytes and more, as well as keeps hydration in the strata corneum to ensure the elasticity and softness of the complexion. A deteriorated skin barrier function may lead to a weakened, unattractive complexion and trigger various skin problems that induce the chronic causes of sensitive, dry, and atopic skins. |
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| The skin barrier, which is made up of keratinocytes and lipids, is crucial in the protective function. Recent researches found that the lipids between keratinocytes are the most important factors for the skin barrier. The lipids consist of ceramides, cholesterols, fatty acids, and etc., and have a unique lamellar liquid crystalline structure. In particular, ceramides account for about 50% of the lipids between keratinocytes and have the function of forming the lamellar liquid crystalline structure. For example, if ceramides are reduced, this will weaken the lamellar liquid crystalline structure, and eventually the skin barrier will be affected. Related skin problems include sensitive, dry, and atopic conditions. Thus, those who have constantly experienced such problem/s should use the skincare products aimed to effectively restore the skin barrier system. |
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| (ii) Lipids and Natural Moisturizing Factor |
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| Epidermal lipids are thin lipid membranes of the skin surface, and include lipids that are created in the lipid gland and pass to the epidermis. The lipids between keratinocytes are created during the keratinization process. When a large quantity of lipids exists, they consist of triglycerides, squalene, waxester, and etc. These particular lipids determine the individuals’ skin types such as oily, dry, and normal skins according to their secretion amounts. Lipids prevent the dehydration of the skin and the surface intrusion of moisture. |
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The natural moisturizing factor (NMF) consists of water-soluble amino acids, lactic acids, pyrrolidone carboxylic acids (PCA), urea, giving it a high moisturizing power. It also has the combining properties with external moisture, thus functioning to provide and maintain its balance in the strata corneum.
However, the NMF’s functions to moisturize and protect skin are temporary. More essential functions come from the skin barrier formed by the keratinocytes and lipids in between.
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| (iii) Weak Acid of Skin Surface |
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| The skin surface’s pH has the low acidity that is fatal to inhibit the breeding of bacteria and germs, and helps the barrier to function properly. |
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| The pH of skin surface varies depending on the individuals, but on average ranges from 4.5 to 6.5. Normal skin’s pH is between 5.0 and 5.5. If the normal pH balance is broken, the bacteria will breed, causing the skin problems and the weakening the skin barrier. |
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Skincare tips: Regular soaps and detergents are alkaline. Immediately after washing with soap, the skin’s pH becomes alkaline, and the skin’s natural restoration ability produces the low acidity in 2 – 4 hours. However, the skin washed with alkaline soaps or detergents has a lower restoration ability, thus delaying the restoration and causing various problems. The typical example is the atopic dermatitis. The pH balance of the skin experiencing atopic dermatitis is
very close to the normal skin types, but the use of regular alkaline soap may worsen the symptoms
If your skin becomes irritated after using a regular alkaline soap or detergent,
we advise you to use the neutral or lower acidity cleansers.
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| Skin is the most outer surface of our body that is in direct contact with the environment plays a crucial role in protecting and keeping the interiors of the body safe. Specifically, our skin has the functions of protecting and storing of moisture, supplying nutrients, and sensing touch. |
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| (i) Skin Protection |
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| The skin barrier system, with the function of skin protection, prevents external intrusion of impurities and loss of body moisture, electrolytes, and etc. If this function is lost, the moisture, electrolytes, proteins, and more will be emitted from the body. The loss allows an easy intrusion of external stimulants, allergic substances, germs, and other pathogens, which cause various skin problems to skin diseases, such as atopic dermatitis. The skin with a weakened protection system includes sensitive, dry, and atopic skins and lacks the ceramides among lipids between keratinocytes |
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| (ii) Moisturizing |
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| Another important function of the strata corneum is to moisturize skin. By maintaining moisture in the strata corneum, the skin can remain elastic and hydrated. Because, a weakened function of moisturizing will make skin dry, coarse, or itchy. The natural moisturizing factor and the lamellar liquid crystalline structure of lipids between keratinocytes are responsible for the moisture balance. In particular, moisture combined in the lamellar liquid crystalline structure of keratinocytes lipids does not easily dehydrate unless the function is abnormally disrupted. |
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| (iii) Function of Percutaneous Absorption |
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The strata corneum provides the path for the drug delivery system or for absorbing useful substances. Percutaneous absorption is to send substances from the skin surface into the dermis via strata corneum or pores. Normally, since the strata corneum have a strong barrier function, they greatly limit absorption of substances according to their properties.
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The stratum corneum (SC) of our skin consists of keratinocytes and lipids between corneocytes, thus serving as a skin barrier. Crucial to such skin barrier are corneocytes lipids. Lipids between keratinocytes consist mainly of ceramide, cholesterols, and fatty acids and by forming a multi lamellar liquid crystalline structure, they serve as a skin barrier function by attaching and enveloping corneocyte cells together. Ceramides are a core component (about 50%) in the formation of the lamellar liquid crystalline structure. If lamellar liquid crystalline structures are not properly formed, this will weaken the barrier wall, resulting in skin damage vulnerable to external environments (allergies, irritations), severe dryness and eventually could cause atopic eczema type skin disorders.
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