General Information

The skin is the largest organ of the human body with several important functions to perform. It covers an average area of 17 to 21 square feet and composes approximately one-sixth of the body's weight. Skin covers the entire body, ranging in thickness with the thinnest skin found on the eyelid and the thickest skin found on the palms of the hand and the soles of the feet.

Skin continually renews itself. Old skin cells are gradually shed and replaced by new ones, with most cells being replaced every 28 days. Our skin is almost completely waterproof, making it our natural raincoat. It stores water and fats and regulates our temperature. Like most of the body, skin contains a high percentage of water. As it is exposed to the sun and wind, skin is at more risk of drying out than any other parts of the body. If it dries out this can cause skin disorders. Moisturized skin is healthy skin.

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What makes up our skin?

Skin consists of three layers. The outer layer is called the epidermis and the middle layer is called the dermis. Beneath the dermis is the subcutaneous fatty layer.

1. The epidermis
The epidermis is made up of 4 layers, the 2 most important of which are the stratum corneum (horny layer) and the stratum basale (basal layer). The horny layer consists of dead, flattened cells. These cells are constantly being shed and replaced by cells from deeper layers. The cells in the basal layer are continually dividing to produce new cells. The old cells are pushed up to the horny layer where they become flatter, die and become part of the horny layer.

• Sweat glands
  These glands produce sweat, which evaporates to cool you down if you get too hot.
  
  
• Hairs
  Hairs grow from pits in the dermis called hair follicles. When the body gets cold the hairs stand on end and act as an insulator to keep you warm.
  
  
• Sensory nerves
  Sensory nerves in the dermis allow you to detect temperature, pressure and pain.
  
  
• Sebaceous glands
  These glands produce an oily substance called sebum. This keeps the skin moist, supple and waterproof. It also stops the hairs from becoming brittle.
  
  
• Blood vessels
  Blood is carried from the heart to the skin by arteries. It is then carried back by veins.
  
  

3. The subcutaneous fatty layer
The subcutaneous fatty layer, or subcutis, consists of loose connective tissue and fat.

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What does our skin do?

The skin has many vital functions, which include protecting your body, keeping it at the right temperature and acting as a sensory organ.

Regulating your body temperature
The skin helps to regulate body temperature, keeping it at a constant temperature of 37.0 degrees C (98.6 degrees F). How does it do this?

• When you're hot
  Sweat glands produce sweat, which evaporates from the skin to cool you down. At the same time, your blood vessels dilate so that they can carry more blood and heat away from the central organs. This is what gives you a flushed appearance.

• When you're cold
  Hairs on the skin stand on end, trapping air, which acts as an insulator. The blood vessels constrict so that less blood is exposed to the surface. This helps to conserve heat and gives you a 'blue' appearance. Fat under the skin also acts as an insulator.

Protecting your body
One of the main uses of the skin is to protect the body against various environmental factors. If the skin's protective mechanisms stop working for any reason, this can often lead to a skin disorder. How does the skin protect the body against different factors?

• Bacteria
  The epidermis prevents bacteria and other microorganisms from entering the body. Cracks in the epidermis allow them to enter and cause infection.

• Mechanical damage
  The layer of dead cells on top of the epidermis protects the body from gentle damage while the subcutaneous fat acts as a cushion against strong blows.

• Ultra Violet rays
  If UV rays from the sun reach the dermis they can damage the skin causing premature ageing and an increased risk of skin cancer.

• Evaporation
  The epidermis is covered in oily sebum and lipids. These waterproof the skin and protect it from losing water, which is vital to its health.

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