UNDERSTANDING HAIR GROWTH
- December 30, 2014
Hair has always played an important role on a cultural and individual level. Historically, healthy hair has been a sign of wealth and status, often conveyed through the use of elaborate wigs, and the desire for a full head of healthy hair continues to the present day, with whole industries revolving around the aesthetics of hair. Traditionally, healthy hair is considered to be a sign of good overall health, with a number of scientific studies supporting this belief. Researchers have shown that a decrease in the quality of hair is an indicator of deteriorating health, due to improper nutrition, chronic disease or aging, and an understanding of the structure and biology of hair supports this belief.
Each strand of hair consists of three distinct parts:
Each strand of hair grows from a hair root, which resides in a hair follicle. At the base of the hair follicle is the dermal papilla, which is absorbs nutrients supplied by blood vessels. Cells of the dermal papilla also contain receptors for hormones, such as testosterone and DHT, which have an impact on hair growth. Matrix cells, found in the hair follicle, obtain nourishment and growth factors from the dermal papilla and differentiate into the various cells that make up a strand of hair. In the case of improper nutrition (e.g. iron deficiencies), hormonal imbalances and certain chronic disease states (thyroid conditions), matrix cells do not receive appropriate nutrients and signals from dermal papillae cells, leading to a change in hair structure and growth patterns. Matrix cells and cells of the dermal papilla undergo changes through the hair cycle, which governs the growth rate of hair.
The Hair Cycle
Hair follicles grow in a cyclic manner going through three distinct phases:
The Anagen Phase: In the Anagen phase, or growth phase, matrix cells are rapidly dividing and differentiating into the various cells that form each strand of hair, believed to be dividing every 18 hours. Under normal circumstances, approximately 85% of all hairs are expected to be in this phase at any given time. The Anagen phase can last anywhere from 2 to 6 years, and the length of this phase determines the length of hair, which is depends on the continued growth of the matrix cells at the follicle base.
Towards the end of the Anagen phase, the rate of growth and differentiation of matrix cells slows down, and the hair follicle moves into the Catagen phase.
The Catagen Phase: The Catagen phase, or transitional phase, lasts one to two weeks. During this phase, the hair follicle shrinks to 1/6th its size, cell growth stops and the dermal papilla breaks away from the follicle. The hair shaft seals off to form a rounded structure (the ‘club’), which continues to move upward.
The Telogen Phase: Following the Catagen phase, hair follicles enter the Telogen or Resting phase. The Telogen phase lasts 5 to 6 weeks, and 10-15% of hair follicles are believed to be in this phase at any given time. Follicles lie in a dormant phase, and no cellular activity takes place.
Towards the end of the Telogen phase, stem cells are activated and cells near the dermal papillae begin to divide. This leads to the formation of a new hair bulb, which leads to the formation of a new hair. The old club hair may be shed (known as Exogen). The new hair bulb enters the Anagen phase, and the cycle is repeated.
It is evident that the hair cycle is essentially a variation in cell division and growth. Like all cells of the body, hair cells also need specific nutrients to grow, and an absence of these nutrients, or a change in an individual’s health that affects cell growth, can impede the process of cell division and cause hair loss. As hair and skin are the most noticeable of our body’s multiplying cells, deterioration in the quality of hair and skin is often an indicator of an underlying condition, which very often, is the outcome of improper nutrition.