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Skin functions and structure

Understanding the functions and roles of the skin

The skin is an amazing organ with functions vital for the workings of the whole body. The right care helps to preserve its health and beauty. To understand the skin’s function for the body and the true meaning of skincare, it may help to know some basics about the skin.
The skin helps us stay alive in various ways as a barrier between the body and the outside world. Physiologically, the skin serves as a protective film, as a heat exchanger, and as a sensor. Skin also plays an important role aesthetically. The appearance and condition of the skin, what we call the ‘complexion,’ reflect a person’s beauty and physical health.

Skin as a protective membrane

The skin protects the body from physical shocks and the infiltration of foreign substances such as chemicals or bacteria. At the same time, it prevents the body losing too much moisture.

Skin as a heat exchanger

The body maintains its temperature at around 37°C by constantly regulating the heat released from the skin. If heat stores up inside the body and the body temperature rises, the capillary vessels of the skin open and heat escapes through the skin surface. If this doesn’t cool the body enough, the body cools itself further via the evaporation of perspiration. When the body temperature falls due to cold, the capillary vessels contract and the flow of blood slows down. This creates a physiological condition that minimizes the escape of heat from the skin surface.

Skin as a sensor

When the skin touches the outside world, it senses texture, pressure, and temperature. Receptor cells inside the skin carry this constant stream of information to the central nervous system. Skin also registers pleasures, such as the healing sensations of a massage or the soothing textures of cosmetics.

Skin as a mirror

The skin reflects the condition of the body and spirit. Physical problems or mental and lifestyle stresses affect the color and moisture level of the skin. To some extent, people make judgments about a person’s health from the appearance of the person’s skin.

The structure and function of the skin

The largest organ of the body

The skin has a surface of 1.6-1.8 m2. It is the largest organ of the body and makes up about 16% of its entire weight (including the subcutaneous tissue). A 50 kg body, for example, normally consists of about 8 kg of skin. The facial skin has a surface area of about 630-850 cm2 (for comparison: one sheet of A4 paper has a surface area of 625 cm2).

Structure of the skin surface

The surface of the skin contains follicles inside which the sebaceous glands (oil producing glands) open so that the sebum generated within is able to pass through the follicles to be secreted onto the surface of the skin. The skin furrows extend radially from the follicles providing links to the nearby follicles. The area surrounding these grooves consists of skin ridges. These contain openings for the sweat glands, through which perspiration is emitted during hot weather. The pattern generated by these furrows and ridges is what we know as the texture of the skin. The shape and size of the texture differs depending on factors such as the area and properties of the skin and gender. Other influential factors include the season and age.

Understanding the structure of the skin

Our skin is divided into three layers: the epidermis on the surface, the dermis in the middle, and the subcutaneous tissue deepest down. Each layer protects the body in a different way.

  • Epidermis
    The epidermis, the uppermost layer of skin, protects us from external irritation. It tends to be very thin, with a thickness of no more than around 0.1-0.3 mm. The epidermis is itself divided into four layers: the stratum corneum, the stratum granulosum, the stratum spinosum, and the stratum basale. Epidermal cells are constantly being created on a 28-day cycle of rebirth and decay. We call this the “turnover” of the skin.
  • Dermis
    The dermis is the middle layer sandwiched between the epidermis and subcutaneous tissue. With a thickness of 1-3 mm it is ten-times thicker than the epidermis. The dermis provides the firmness and elasticity of the skin. It is mainly made up of collagen (which provides firmness), elastin (which provides elasticity) and polysaccharides such as hyaluronic acid.

    The dermis is made up of 60-80% water and provides moisture to the epidermis. It consists of blood vessels (to supply nutrients to the epidermis), lymph vessels, receptors, and nerve endings. The dermis tissue also accommodates the sweat and oil glands extending out to the epidermis.
  • Subcutaneous tissue
    The subcutaneous tissue, located beneath the dermis, is made up mainly of subcutaneous fat. The subcutaneous fat cushions the bones and muscles from external shocks and maintains body temperature via an insulating function. It also stores energy in form of fat cells. The thickness of subcutaneous tissue is determined by the amount of fat, a condition that varies considerably with body type, age, and also gender.

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Skin types:
Knowing your skin type

Healthy and beautiful skin has a fine, even texture and just the right balance of water and sebum. Skin beauty comes when all of the skin functions work together in optimal balance.

Skins vary in the amounts of sebum they secrete and in their efficiency in preserving moisture inside the stratum corneum. The combinations of these two skin properties determine which skin type a person has – normal skin, dry skin, oily skin, or combination skin.

The best way to tell the skin type is to look at the skin condition of the face. First, look at sebum secretion in the T-zone, the area prone to oiliness from the forehead to nose. Next, look at the moisture content of the so-called U-zone, the area prone to dryness over the cheeks and around the eyes.

The four skin types

Normal skin

The T-zone secretes sebum at a moderate level. The U-zone has sufficient moisture.

  • The sebaceous glands are overactive and produce too much sebum.
  • The stratum corneum retains ample moisture and forms a reliable barrier function.

Oily skin

The T-zone produces too much sebum. The U-zone has sufficient moisture.

  • The skin is free from excess sebum, as the sebaceous glands (the glands that produce oil) are working at a normal level.
  • The stratum corneum (the outermost layer of the epidermis) retains moisture and forms a reliable barrier function.

Dry skin

The T-zone secretes sebum at a moderate level. The U-zone lacks moisture.

  • The skin is free from excess sebum, as the sebaceous glands are working at a normal level.
  • The stratum corneum lacks moisture and has a low barrier function.

Combination skin

The T-zone produces excessive sebum. The U-zone lacks moisture.

  • The sebaceous glands are overactive and produce too much sebum.
  • The stratum corneum lacks moisture and has a low barrier function.

To learn about the quality of your skin in more detail, have it examined by a Kanebo beauty consultant.

Measuring skin type at a cosmetics counter
Kanebo beauty consultants at leading retailers of Kanebo Cosmetics products use skin measurement devices to assess the skin types of customers individually. These devices measure not only skin moisture, but also skin color and clarity, the condition of the pores, and even the condition of the dermis and epidermis. These assessments help our beauty consultants select the best products for the customer’s skin and advise the customer on how to care for her skin in daily life.

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Causes of skin damage

Several factors can cause damage to the skin. A healthy, beautiful skin condition is unachievable with cosmetic alone, no matter how effective those cosmetics may be. To make the most of skincare cosmetics, one should first understand the factors that impair the skin beauty.

Three main factors of skin damage

The three main factors affecting skin beauty are UV rays, cold, and dryness.

Ultraviolet rays

  • Trigger pigmentation and thickening of the horny layer to protect the skin from further UV exposure
  • Lead to wrinkles and sagging in response to degeneration of collagen and elastin

UVC UVB UVA

Ultraviolet rays from the sun come in three wavelengths: UVC (short-wavelength UV), UVB (medium-wavelength UV), and UVA (long-wavelength UV). UVC light is blocked by the ozone layer surrounding the earth. UVB light is blocked partially but can still damage the skin. UVA reaches the earth’s surface at full strength and damages the skin in several ways at once.

  • Effect of UVB rays
    UVB rays penetrate the upper skin layers and cause acute inflammation, or what we know as sunburn. Several days later the inflammation turns into a suntan.
    UVB has strong irritant effects on the skin: its capacity to cause inflammation is almost a thousand times greater than that of UVA. UVB also damages the DNA of epidermal cells. Continuous UV exposure over a long period not only causes deep wrinkles and dark spots, but can lead to skin cancer.
  • Effect of UVA rays
    UVA isn’t as powerful as UVB, but it deeply penetrates the skin all the way into the subcutaneous tissue. Exposure to UVA triggers immediate pigment darkening.

    Long-term exposure damages fibroblasts, collagen fibers, and elastin. This results in a loss of skin firmness and resilience and induces deep wrinkles and dark spots. These changes associated with UVA exposure are known as “photo-ageing” in distinction to normal ageing.

    Unlike UVB light, UVA can pass through ordinary window glass. Most UVA rays reach the earth’s surface even on cloudy days, steadily damaging the skin in a cumulative fashion in everyday life.
  • Effective use of sunscreen
    The packages of cosmetics with UV block usually show two factors that indicate the strength of UV protection: SPF and PA factors. The SPF rating indicates the product’s strength in blocking UVB rays. The PA indicates its strength in blocking UVA.
    Sunscreen should be applied evenly wherever the skin is exposed to sun. Remember that a single application is seldom enough: apply carefully every few hours for reliable protection against sunburn.

Cold

When cool breezes from air-conditioners or cold winter winds blow against the skin, the capillary vessels shrink. This slows down the blood circulation and metabolism, which causes chapping, fine lines, and skin dullness.

As a defense against the cold, the blood vessels of the skin contract in order to draw out warmer fluids flowing deeper inside the body. While this defense is effective in preventing cooling, it also impairs the blood circulation. The slowdown of blood flow inhibits the supply with oxygen and nutrients and the collection of carbon dioxide and waste products ejected from the cells.

To protect the skin against cold, as much of the body apart from the face should be protected in clothing. If possible, skin massage should be worked into the daily skincare routine to stimulate microcirculation.

Dryness

Inside a room with heating or cooling, the dry air deprives the skin of moisture, which results in chapping, fine lines and dullness.

The capacity to maintain moisture declines as a person gets older. Moisturizing skincare protects the skin from dryness and helps to preserve the youthfulness of the skin as the years go by. Moisturizing can also prevent the skin inflammation accompanying dryness.

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