The Biology Behind Hair Growth
Below is a MRR and PLR article in category Health Fitness -> subcategory Beauty.
The Biology of Hair Growth
Overview
Discover the fascinating biology behind hair growth, including how hair develops, why it regrows after removal, and the various stages involved.
Hair Anatomy
Hair is a complex structure with a remarkable biological process. It starts to form while we are still in the womb, with a developing fetus having around 5 million hair follicles by 22 weeks. This is the total number of follicles we will have for life, as no new ones are formed after birth.
Structure of Hair
Hair consists of two main parts: the follicle and the shaft. The follicle is embedded in the skin and contains several layers, each with a unique function. At its base lies the papilla, connected to capillaries that supply blood to surrounding cells at the bulb.
There are two sheaths around the follicle: an inner and an outer one. These sheaths protect the hair shaft and guide its growth. The inner sheath ends at the sebaceous gland, while the outer sheath extends to the erector pili muscle, which causes hair to stand up when it contracts.
The hair shaft itself is composed of three layers of keratin, a type of protein. The innermost layer, the medulla, isn't always present. The middle layer, the cortex, is the bulk of the hair and determines its color. The outermost layer, the cuticle, consists of overlapping cells that give hair its shine.
The Hair Growth Cycle
Hair on the scalp grows around six inches per year, or about 0.3 to 0.4 mm per day. The growth process involves three distinct phases:
Catagen Phase
This transitional phase lasts about two to three weeks and involves about 3% of your hair at any given time. During this period, hair growth ceases as the outer root sheath shrinks and attaches to the root.
Telogen Phase
Known as the "resting period," this phase includes roughly 15% of your hair and lasts around 100 days for scalp hair, significantly longer for other body hair.
Anagen Phase
This phase is characterized by active cell division and new hair growth. It can last from two to six years. People with shorter growth periods may find it difficult to grow their hair long.
Hair Growth Disorders
Several disorders can affect hair growth:
- Hirsutism: Predominantly affecting females, this condition results in excessive dark and thick hair growth in areas typically associated with male hair patterns, such as the face, chest, and around the nipples.
- Hypertrichosis: This causes excessive hair growth in areas not usually hairy and can occur on various body parts.
Both conditions are treatable, helping those affected manage their symptoms effectively.
In summary, hair growth is not just a basic process but a complex one with distinct phases and layers. Understanding its biology can illuminate why hair grows, regrows, and sometimes behaves unusually.
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