THE STRUCTURE AND FUNCTION OF SKIN
   

Here are a few amazing numbers:
   

• Skin’s surface area measures between 1.8 and 2m². It is therefore the largest as well as the one of the most sensitive organs in the human body.
• Skin weighs about 14 kg on average per person, accounting for about 20% of our total body weight.
• Each square centimeter of skin contains 5 million cells, 150,000 pigment cells, 5,000 sensory cells, 100 sweat glands, 15 sebaceous glands and 5 hairs, in addition to 4 meters of nerves and one meter of blood vessels.
• Skin is 2 to 4 mm thick on average.
• Each of us loses about 1 gram of dead skin cells daily, which amounts to roughly 20-25 kg over a lifetime.
• Skin regenerates itself every 28 days. This process takes place in the epidermis.

The Structure of Skin
   
Skin consists of three layers:

• Epidermis: The epidermis is comprised of five layers (from the inside out): the basal layer, prickly layer, granular layer, clear layer and horny layer. Skin regeneration takes place daily through cell division in the basal layer. Every 28 days, cells travel from the innermost to outermost layer of the epidermis. During this process, they die and are eventually shed.

• Dermis: This layer is divided (again from the inside out) into the papillary and reticular layers. It contains blood vessels, nerves and connective tissue. Hair roots are also embedded here. The connective tissue is formed from collagen and elastin fibers and is responsible for the skin’s tautness- i.e., its flexibility and elasticity.

• Subcutis: The subcutis is comprised of only a single layer and differs from person to person in thickness, because it contains the fat cells. The subcutis stores energy for the body by acting as a nutrient reserve and helps protect it from cold and injury.

The Function of Skin
   
Skin fulfills a wide array of important functions. It serves first and foremost as a:

• protective organ and barrier. Supported by the hydrolipid film (also called the acid mantle), a mix of sweat and sebum from the horny layer, skin protects against
• cold, heat and sun exposure
• water and heat loss
• chemical substances in the environment
• microorganisms, germs and other foreign substances.
• It is therefore an important part of the body’s immune defense system.
• storehouse: stores fat, water, minerals and vitamins in the skin. It acts as a depot for the body during the “hard times” (e.g., during dieting).
• protection from pressure, friction and impact
• excretion: Sweat, sebum, and metabolic waste are excreted through the skin.
• absorption: absorbs oil, water and various outside substances
• heat regulator: The skin regulates body temperature through hair, fat tissue and sweat glands. Perspiration—or sweat evaporation—helps the body maintain a constant temperature of 36.5° C.
• sensory organ: Temperature, touch, vibration, pressure, pain and pleasure are all perceived through the skin.
• metabolic organ: While skin protects the body from damaging substances, it also absorbs beneficial substances and transports them further throughout the body. Blood circulation in the skin, as well as its absorption of vitamins, helps to stimulate the body’s overall blood circulation. This is because skin, in combination with sunlight, is responsible for producing essential vitamin D.

       
The Role of the pH-Value
   
The pH value—or level of acidity—plays a large role when selecting the right skin cleanser or moisturizer. This is determined on a scale of 1 to 14; under 7 is acidic, 7 is chemically neutral and over 8 is alkaline. The pH value of the acid mantle of healthy skin lies between 4.2 and 6.2, which means that the skin is slightly acidic. When cleansing and moisturizing products are within this pH range, they are gentler to the skin.

Substances that possess a higher pH range can have an aggressive effect on the skin. For example, if a soap with a pH value of 9 to 12 is applied, the pH value of the skin’s surface will temporarily be altered to within alkaline range. The natural protective capacity of the skin is thus impaired, and skin can react sensitively. With normal skin, the original pH value is quickly restored without any ill effects.