The Anatomy of Human Hair And Hairloss
The human body has about five million hairs, with 100,000 to 150,000 on the scalp. Hair is composed of a protein called keratin. Keratin also makes up the nails and outer layer of skin. Beneath the skin, the hair has a root, which is surrounded by a small sack of cells called the hair follicle. At the bottom of the follicle is the papilla. This is where new hair cells are manufactured.
The papilla and follicle is supplied blood, oxygen and nutrients as well as cleansed of metabolic and toxic waste by capillaries, tiny blood vessels. Hair growth is regulated by androgens, male hormones such as testosterone. Other androgens include dihyrdo-testosterone (DHT), which is a converted form of testosterone, and two adrenal androgens; dihydroepiandrosterone (DHEA), and androstenedione.
Scalp Cross Section
Hair has a life cycle of three phases; anagen (active growth), catagen (in between stage), and telogen ( resting, no growth). The anagen phase is where protein synthesis and keratinization are actively occurring. This phase lasts for up to five years. When active growth stops, a transitory stage lasting two or three weeks called catagen occurs.
The hair has stopped growing and the follicle is contracting or shrinking, but is still lodged in the scalp when it enters the resting, or telogen phase. This phase may last for up to 12 weeks before a new hair, or bulb, dislodges the telogen hair from its follicle. Washing or brushing may also dislodge these hairs.
People shed from 50 to 100 hairs each day, and hair may grow up to one-half inch per month. It has been shown in studies that hair grows faster in the summer and slower in the winter. Heat stimulates growth and cold hinders it. As hair is shed and newer hairs grow in their place, each new strand may become finer and thinner than the previous.
After several months or years, this process produces changes in the appearance, leading to what is known as baldness or male pattern baldness (MPB). This may be characterized also by the hair that falls off having a bulb attached to it. This is a significantly sized mass of skin and hair cells. Women may also experience this condition, though typically not as severe due to less circulating levels of androgens.