Your skin is the largest organ in the human body.  Skin is often overlooked as an organ however it portrays the same definitions and characteristics of an organ.  The way she skin works is amazing. 

 Looking closely at the skin you can see that it is made up of two main layers.  These layers are called the epidermis which is on the outside and the dermis which is on the inside.  The epidermis is the main barrier that protects the body from damages such as abrasion and sunlight.  The dermis is the part that contains all the important stuff such like nerve endings, sweat glands, hair follicles and much more.  The image below shows the main bits and pieces.

 

The subcutaneous layer contains the blood vessels shown as blue and red lines mixed with subcutaneous fat.  The blood vessels branch out in a pretty much infinite pattern into the dermis to supply all the major bits like the sweat glands and hair follicles.  As well as this they also get into dermis’s capillary bed.  The dermis is loaded with capillaries so that it can be fed and also perform the important cooling function of the skin. The epidermis does not have a direct blood supply but is fed by the dermis.

 The dermis is indeed the clever bit of the skin.  It contains the sweat glands and hair follicles that have there own tiny muscles that make your hair stand on end!  There are also millions of nerve endings that sense heat, cold, pressure, pain and itching.  The epidermis is the interface to your outside world.  The interesting part about the epidermis is that it consists of a living part on the inside and a dead part on the outer layer.  The dead layers are pushed outward by new cells, looking carefully at the skin you will often see small amounts of flaking or just after healing you may see increased amounts of dead skin on the surface.  Pealing after sunburn is simply the accelerated process of your skins natural cell replacement. 

 The inner layer is called the Malpighian layer and this is what creates the dead cells that we can see.  It is this part of the skin that is affected during sun tanning.  The Malpighian layer is layered like this

• In direct contact with the dermis is the basal layer. If you have ever heard of a basal cell carcinoma (cancer), this is where it starts.
• Above the basal layer is the spinous layer.
• Above the spinous layer is the granular layer.
  

Is your head hurting yet??  Grab some aspirin and stay with us.

 Located above the granular layers is the stratum cornenm or in English the outer layer of dead cells that we see as our skin.  These cells contain large amounts of a protein called keratin.  This ketarin is basically the same stuff that your hair, fingernails and toenails are made up of.  The same protein makes up hooves and horns on animals.  Your skin is the same stuff just made up of a more thinner and flexible layer.  The layer is thicker in obvious areas where it needs to be such as the hands and feet. 

 
Now you have an understanding (we hope but doubt) we will move on to what exactly caused tanning. 

Among the Malpighian layer is another type of cell called melanocyte which produces a chemical called melanin.  This is a pigment and the cause of tanning.  The melanocytes are where your tan comes from.  Below is the Encyclopaedia Britannica explanation of melanocytes:

The appearance of the skin is partly due to the reddish pigment in the blood of the superficial vessels. In the main, however, it is determined by melanin, a pigment manufactured by dendritic cells called melanocytes, found among the basal cells of the epidermis. Their numbers in any one region of the body, which range from about 1,000 to more than 2,000 per square millimeter, are roughly the same within and between races; the blondest whites have as many as the darkest blacks. Color differences are due solely to the amount of melanin produced and the nature of the pigment granules. When the skin becomes tanned on exposure to sunlight, the melanocytes do not increase in number, only in activity." ("Integumentary Systems, Pigmentation", Britannica CD. Version 97. Encyclopedia Britannica, Inc., 1997.)