Any topical stimulus destined to influence and manipulate internal or external organs must start at skin level. The skin is the largest organ, containing fluid, blood, blood vessels, connective tissue, muscle and rich nerve supplies. The body’s first direct contact with the outside world is through the skin. The skin is the mirror of one's health, and when in good health, the skin is shiny, tight, and has a smooth texture. It responds to changes in temperature and is generally warm when touched. When the body is unhealthy, however, a dull, rather lifeless skin appearance is evident, with little natural color and often cold to the touch.
As well as protecting the body from external pathogens, the skin has a major role in a number of body functions. It is the main organ of sensation, through many millions of nerve endings contained in its structure. A rich network of blood vessels and glands provides an effective means of temperature control. There are two main layers of the skin which included the outer epidermis and the inner dermis. The fatty subcutaneous region lies beneath these two. The epidermis is the cellular layer of the skin, varying in thickness from 0.1 mm in the eyelid to over 1 mm on the palms of the hands and soles of the feet. It has no nerves, connective tissue, or blood vessels.