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.
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 epidermis2. The dermis
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.
Some of the features of the dermis
are as follows:
These glands produce sweat, which evaporates to cool you down if you get too
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 in the dermis allow you to detect temperature, pressure and
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 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
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?
The epidermis prevents bacteria and other microorganisms from entering the
body. Cracks in the epidermis allow them to enter and cause infection.
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.
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.