Overview of human hair
Human hair can be very complex. While it acts as a barrier to foreign particles, it also transmits sensory information. Besides, it has the ability to rejuvenate itself without any scarring. Although hair anatomy seems pretty straightforward, it is one of the most intricate structures of the body. Made up of two different components, the follicle, which lies below the skin and the shaft, that is visualised above the skin's layer, the hair on the scalp goes through a cycle where it grows about 6 inches per year and half a millimetre per day.
Hair comes with several advantages. For one, it regulates body temperature. It particularly conserves heat when you feel cold. The hair on the scalp also shields heat and cold. Every strand of hair takes about 2 to 6 years to grow. At the same time, humans experience hair loss of about 50 to 100 hairs per day.
It also protects the body against ultraviolet damage.
Scalp hair assists in stabilizing the brain's temperature.
Background of human hair
Hair finds its origins in mammals around 300 million years ago from the synapsids who were our ancestors. Comparatively, human hairs have less pigment and are even more miniaturized than in apes. As far as the hair cycle is concerned humans have shorter telogen phases and longer anagen phases. There are innumerable genes involved in the formation, growth, and cycling of the hair follicle.
The Cycle of Hair growth
Primarily hair cycles through three main phases - Anagen, Catagen and Telogen.
Anagen: This is the first part of the growth cycle, where the hair bulbs quickly divide to form new hair. The stage can last anywhere from 2 to 7 years.
Catagen: Also known as the transition phase, the stage lasts no more than 2 to 3 weeks. Club hair develops where hair stops growing and detaches itself from the blood supply.
Telogen: The resting or telogen phase, is where newer hair grows beneath the club hair to replace it. Lasting for about 3 months, at any point in time, about 10 to 15% of hairs are in this phase.
A protein filament growing from the follicle, embedded deep within the dermis, the hair strand shoots out of the epidermis and is one of the most defining characteristics of mammals. While the growth rate of hair differs from individual to individual, the average rate stays at about 0.3 to 0.4 mm per day. The colour of the hair is derived from melanin a pigment produced in the hair follicle. About 5 million follicles are developed by a human foetus at just 22 weeks of gestation. For the rest of our lives, we do not generate any fresh follicles!