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16 April 2014
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You are here: BBC Science > Human Body & Mind > The Body > Organs
Fact files

Organs - Skin

System: Integumentary

Location: All over your body

Physical description: Flat, pliable and tough, between 0.5 and 4mm thick

Function: To protect your body from damage, infection and drying out

Largest organ

Your skin is your largest organ. It covers your entire body and has a surface area of around 2 square metres. Its thickness varies from 0.5mm on your eyelids to 4mm or more on the palms of your hands and the soles of your feet. In total, it accounts for around 16 percent of your body weight.

Tough physical barrier

Your skin consists of two main layers: the outer epidermis and the inner dermis.

Cells in the deepest layer of your epidermis divide constantly to make new cells. The new cells are pushed towards the surface of your skin. They eventually die and become filled with keratin, an exceptionally tough protein. Keratin provides your body with a durable overcoat, which protects deeper cells from damage, infection and drying out.

Cells on the surface of your skin rub and flake off steadily and are continuously replaced with new ones. About every 30 days, your body produces a totally new epidermis.

Your inner dermis consists of strong collagen and elastic fibres pierced by blood vessels. It also contains touch, pressure and pain sensors and is packed with hair follicles, sweat and oil glands. The oil glands produce a lubricant that keeps your skin soft and prevents your hair from becoming brittle.

Temperature control

Your skin's blood vessels, sweat glands and hairs play a crucial role in regulating your body temperature. When you need to cool down

  • Your blood vessels widen and allow heat to escape through your skin
  • You start sweating, and as your sweat dries, it uses heat from your skin and cools you down
  • Your hairs lie flat to make sure little warm air doesn't get trapped between your skin and your hairs

When you need to retain heat, the opposite happens – your blood vessels narrow, you produce less sweat and your hairs stand up on end to trap warm air around your body.

Skin colour

Your skin contains specialised cells called melanocytes. They produce melanin, a brown substance, which absorbs some of the Sun's harmful ultraviolet rays. Fair-skinned people only have melanin in the lower layers of their epidermis. People with dark skin have larger amounts of melanin in all layers. Freckles and moles are nothing else but small patches of skin with more melanin than in the surrounding area.

Wrinkles

As you age, the number of collagen and elastic fibres in your dermis decreases. Additionally, you lose fat from the tissue under your skin. As a result, your skin becomes less elastic and begins to sag and wrinkle.

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