Hair biology information
Welcome to hair biology dot com. This web site explains the biology of hair – how hair follicles develop, how they grow and cycle, and how they are important for our health. Take a look around and I hope you find the information useful!
After the skeleton the skin is the second largest organ in the body. It is also integral to the survival of mammalian life. But its importance is often overlooked with respect to the health and welfare of an individual. The skin structure is heterogeneous and it is derived from the ectoderm and mesoderm of an embryo giving rise to the epidermis and dermis respectively. These generalized layers include in between the specialized appendages that are derived from the ectoderm and/or mesoderm including sensory nerves, sweat glands and hair follicles. The skin as a whole rests on subcutaneous tissue largely composed of a loose mesh of collagen fiber, fat cells and muscle tissue.
The skin of an adult human has been calculated to contain 800 million cells, but these cells are not a homogeneous mass uniformly distributed over the body. In fact, the skin contains many different structures with various functions including, nails, hair, sweat glands, oil glands, apocrine glands, nerve fibers, sensory cells for pressure and heat, blood vessels, and lymphatic vessels.
The density of the different structures in the skin varies considerably with the body location. However, on average about 10 hair follicles and 15 sebaceous glands, 10 sweat glands, half a meter of blood vessels, 2 meters of nerves, with 3,000 sensory cells at the ends of nerve fibers, 200 nerve endings to record pain, 25 pressure receptors for the perception of tactile stimuli, 2 sensory receptors for cold, and 12 sensory receptors for heat can be found in one square centimeter of skin.
Arguably one of the most significant of all these skin structures is the hair follicle appendage. Hair plays key role in providing protection against heat loss. By trapping air adjacent to the skin hair provides an invisible, insulating layer. Several mammalian species produce special dense winter coats with added heat trapping properties. As for example, otters have hair to trap a layer of air around their bodies keeping them warm and making them more comfortable when they swim. Many species go through molting cycles in tune with seasonal changes.
Hair also acts as indicator of development through onset of secondary characteristics. The mane on a male lion and beard development in humans provide some good examples. Hair also plays an important role in attracting mates. The features like color - such as silver back mountain gorillas – distribution or hair, or quality, become indicators of the general health and vitality of an individual and thus influence the mate selection process.
Hair may also assist in camouflage for survival purposes where mute tones or dappled color blend with an animal's environment. Hair fiber also protects the epidermis from minor abrasions and/or from ultra violet light. Specialized hair such as eyebrows and eyelashes protect the eyes from sweat, dust and debris. Nasal hair prevents air borne foreign particles from reaching the lungs by trapping them beforehand. Hair fiber facilitates faster evaporation of sweat from neighboring apocrine glands. Some hair follicles having a highly developed nerve network around them provide sensory, tactile information about the environment. Thus, the hair follicle is of great importance to the survival of mammals.
In recent times, cosmetic and commercial considerations have tried to downplay the importance of skin - but it is still significant. In the modern ages, the secondary functions of hair have earned primary importance for humans. Individual hair styles speak of individual identity, and used to attract a mate. A multi million dollar industry has flourished on the foundation of hair with the focus on presenting, augmenting, and preserving scalp hair and also removing unwanted body hair.