Skin is the second largest organ in human body. It is mainly composed of a loose mesh of collagen fibers, fat cells and muscle tissue. Within the generalized skin layers are special structures including sensory nerves, sweat glands and hair follicles.

Skin performs many important functions such as supporting and covering the underlying tissues, protecting the body from infections, regulating body temperature, maintaining water and electrolyte balance, sensing painful and pleasant stimuli, excretion of waste materials, production of vitamin-D, and growing hair via hair follicles.

The skin keeps dangerous substances from entering the body and provides a shield from the sun's harmful effects. In addition, skin color, texture, and folds help to accentuate an individual’s identity and uniqueness.

Significant in many of these properties is the hair follicle appendage. The key role of hair is to provide protection against heat loss from the scalp. Over one third of all heat loss from a human body passes from the head. Hair traps air adjacent to the skin to provide an invisible, insulating layer. Specialized hair such as eyebrows and eyelashes protect the eyes by channeling or sweeping away fluids, dust and debris. Nasal hair plays an important role in blocking access to insects before they reach the lungs. Hair fiber may also increase the surface area for faster evaporation of sweat from neighboring apocrine glands. Some hair follicles have a highly developed nerve network around them and provide sensory and tactile information about the environment. Consequently, while hair is less important to human survival, the hair follicle is of great importance to the survival of most mammals.

Each hair grows from a follicle deep in your skin. As long as these follicles are not completely destroyed, hair will continue to grow even if the shaft, which is the part of the hair that appears above the skin, is plucked or removed. Hair follicles cover every surface of your body except the soles of your feet and the palms of your hands. Of the approximately 50 million hair follicles covering human body, one-fifth are located on the scalp. The number of hair follicles you have does not change after birth. However, many people experience a slow decrease in hair follicle number from around age 50 onwards.

Hair growth and hair loss is random although there can be a somewhat cyclical nature as hair is often shed at a slightly higher rate than normal in the spring and fall as compared to summer and winter. In general, at any given time, a random number of hairs will be in various stages of growth and shedding. Adults have two main types of hair, vellus and terminal. Vellus hair is soft, fine, generally colorless, and usually short. Terminal hair is long, coarse, dark, and sometimes curly. Terminal hair is made by large hair follicles in the skin while small vellus hair correspondingly comes from very small hair follicles.