Skin is the largest organ of the body, which acts as the first barrier against many harmful external factors. The skin has different layers which are discussed below:


The uppermost layer of the skin is the epidermis, which itself consists of several layers. These layers act as a physical barrier to prevent entrance of bacteria and to prevent water vaporization from the skin. The skin repairs itself in a few days; however recurrent physical damage leads to increased thickness of the outer layers of epidermis and finally callus formation. 
The epidermis also contains melanocytes that protect DNA and cell nucleus against UV radiation. But they may increase in size or number and lead to skin blemishes.


The dermis is right below the epidermis and is composed of elements that are responsible for skin toughness and elasticity. These elements are:
1) Collagen fibers: This is the main skin component that causes skin toughness.
2) Elastin fibers: This protein is the main factor which gives elasticity and flexibility to the skin.
3) Ground substance (matrix): This is an amorphous material that holds a lot of water which is necessary for skin’s freshness and beauty.
Dermis also contains blood vessels and nerves. Blood vessels bring oxygen and nutrients to the skin.


The hypodermis is the innermost and thickest layer of the skin. It is essentially composed of a type of cells specialized in accumulating and storing fats, known as adipocytes. The hypodermis acts as an energy reserve and participates, passively at least, in thermoregulation since fat is a heat insulator. Whilst the hypodermis is distributed over the entire body, it has a tendency to accumulate above the belt over the abdomen and shoulders in men, and in women, below the waist around the thighs, hips and buttocks.