It’s a good thing that your skin does its work on the periphery of your body, because having a 4kg organ in your torso would leave far less room for other essential items such as your heart and liver.
But spreading it in a thin layer around your body means that you seldom know it’s there – makes sense, really.
Your skin regulates your body temperature, forms a physical barrier against injury and infection. It protects your internal organs against external factors dangers such as bacteria and harmful sunlight.
Your skin also plays an indispensable role in regulating your temperature. To keep it at the optimal 38 degrees Celsius (98.6 degrees Fahrenheit), it secretes sweat, then evaporates from bare skin, cooling it.
Additional cooling is provided by dilation of the blood vessels in the dermis, which allows for the heat to dissipate from the blood as it’s pumped through them.
To conserve body heat, the blood vessels contract, restricting blood flow. Hair follicles stand erect, causing the hair to rise, in an attempt to trap a layer of warm air close to the skin. Where the body hair is too thin to accomplish this, it results in goose flesh.
Your skin also forms a physical barrier against injury and infection. The skin’s sebaceous glands secrete sebum, an oil which provides an effective barrier against the growth of bacteria. When your skin is dry it cracks open, allowing in bacteria and reducing its ability to ward off infection.
The skin even operates its own immune system, called the skin-associated lymphoid tissue (Salt), a network of immune cells that recognise and destroy foreign matter, such as bacteria and toxins.
Here's how it works: the strike troops in the war on infection are called Langerhans cells, which are derived from bone marrow. They react immediately to any incursion by foreign matter, then attract white blood cells such as lymphocytes and macrophages to the area. They first prevent the invaders from advancing into the body, then destroy them.