- Skin Structure

“Skin is the largest organ in the human body. Skin has a surface area of 1.6 m2 and comprises 16% of the total body weight.”

Skin is the most important organ in human body. Basic function of skin is integument of the body that protects internal organs and also performs many other functions for body. Because it interfaces with the environment (UV, temperature, moisture, dust, air pollution and so on), skin plays key role in reading information that is essential to the survival immediately and responding appropriately to protect the body. There is an additional function that the skin protects itself from the external harm.

Human skin is divided into 3 main layers: epidermis, dermis, subcutaneous tissue from the outermost layer and also it has some affiliated organs include hair, sebaceous glands, sweat glands, capillary, etc. Epidermis is the thinnest layer of the skin. It is responsible for moisturization and protection of the skin. The epidermis organically consists of keratinocytes, the cells making protein keratin and melanocytes, the cells producing melanin which is the pigment responsible for skin tone and color.

The epidermis is subdivided into several layers (from deepest to most superficial layer): stratum basale, stratum spinosum, stratum granulosum and stratum corneum. Keratinocytes undergo cell division (via mitosis). The newly formed cells move up the strata (stratum spinosum and stratum granulosum) over changing shape and composition as they differentiate and become filled with keratin. They eventually reach the top layer and compose stratum corneum. This process is called keratinization.

The stratum corneum is the outmost layer of the epidermis, consisting of dead cells (anucleate cells). It is comprises only 15-20 flattened cell layers. Because it consists of dead cells, its importance didn’t be recognized in the past. According to the recent studies, the stratum corneum is not only piled with dead cells, but also it is performing a variety of roles. The stratum corneum damage can lead to many kinds of skin problem and skin diseases. In order to maintain healthy skin, it is necessary to correctly understand about stratum corneum and recognize the importance of skin care.

Keratinized layers (stratum corneum) slough off from the skin after a certain period of time, and newly created keratinized layers will come out. This process is called desquamation or turnover. This process is regarded as a defense. Through this progress, unnecessary materials are prevented to remain in the epidermis and discharged from the skin. Turnover takes repeated cycle of roughly 4-6 weeks. Our skin is not retained after once formed, but as a dynamic organ it always repeats the process of production, desquamation and production. If horny generation and shedding period abnormal, there are several kinds of problems can be occurred. Most skin diseases accompanied by abnormal stratum corneum.

The dermis comprises the matrix of typical proteins which are collagen (which plays an important role in providing skin strength) and elastin (which plays an important role in providing skin elasticity). The dermis also contains capillaries, nerves, mastocyto (which involved in allergic reactions) and many natural moisturizing factors (NMF) like Na-PCA and hyaluronic acid (what have an important feature for moisturizing).

The hypodermis (Subcutaneous tissue) consists mainly of adipocytes. This layer is responsible for providing nutrition for epidermis and dermis, supporting the skin structure, absorbing shock, maintaining body temperature and protecting underlying cells from mechanical trauma.