Written by Sonya G. Zarkhin B.S. & Paul M. Graham D.O.
For many years, men have been the poster boys for hair loss. However, hair loss is not just restricted to men. Many women suffer from hair thinning and in severe cases, complete hair loss. Over the course of this three-part series, we will discuss the basic features of hair, how to diagnose and recognize hair loss, and the treatment options currently available to preserve your luscious locks.
Its important to understand that there are more than just one type of hair on the human body. Adults have both vellus and terminal hair follicles scattered throughout the skin. Vellus hair consist of small, fine, light-colored hairs that often remain short and discrete. This is widely known as “peach-fuzz”, as it is barely noticeable on the skin surface. The majority of vellus hair follicles develop during early infancy around the 38-40th week of gestation and remain unchanged throughout puberty. Vellus hair provides both cooling and thermal regulation properties during times of environmental stress. In contrast, terminal hair consists of long, thick, pigmented hairs that cover the scalp, face, groin (genitalia), armpits (axilla), arms, and legs. Terminal hair is sensitive to elevated hormone levels known as androgens (sex hormones), which occurs during the process of puberty (10-11 years old in females; 11-12 years old in males).
The Hair Unit:
Each hair on the human body is part of a pilosebaceous unit. The pilosebaceous unit holds the hair shaft and follicle as well as the sebaceous gland and the arrector pili muscle. Have you ever felt as if your hair was standing on end, causing “goose bumps” to develop? The arrector pili muscle is responsible for this occurrence. In mammals, this muscle is important for body temperature regulation. On the other hand, the sebaceous glands have the ability to protect your skin from water. Sebaceous glands secrete a mixture of oils (lipids) called sebum, which is important in lubricating and water-proofing the skin. Sebum also possess thermoregulatory properties, in which it forms a sheet of oil over top of a thin layer of sweat on the skin to prevent evaporation, further delaying dehydration.
The hair follicle is another important structure of the pilosebaceous unit. It functions to house the hair shaft, allowing for controlled growth to occur. The hair follicle is the primary target for hair transplantation, which contains its own undifferentiated stem cells. During hair transplants, individual hair follicles are extracted from an area of dense terminal hairs (hair on the back of the head) via several surgical techniques and placed into the area of low hair density. Independent hair follicles are harvested and placed into the skin at different angles in hundreds of locations to give the final result. It typically takes up to 12 months before the results of the hair transplant are noticeable. Finally, there are numerous nerves, arteries, and veins that run parallel and perpendicular to the hair follicles. These structures supply each follicle with oxygen, nutrients, and sensation. Together, all of these structures work to protect, maintain, and cultivate hair growth.
The Hair Cycle
- Anagen Phase
During the anagen phase, the hair shaft is actively growing within the follicle. It is the duration of the growth phase that actually determines the final length of the hair. Different locations on the body have varying lengths of the anagen phase. For example, the anagen phase for scalp hairs ranges from 2-6 years as opposed to the anagen phase for arm hairs, which is much shorter at 6-12 weeks.1 This explains why the arm hair is much shorter compared to scalp hair. At the end of the anagen phase, the hair shaft stops growing and transitions into the catagen phase.
- Catagen Phase
The hair shaft stops growing after the completion of the anagen phase and this marks the start of the catagen phase. During this phase, the hair bulb begins to degenerate and the hair follicle slowly migrates toward the surface of the skin. The catagen phase is fairly short and typically last from 2-3 weeks before transitioning into the telogen phase.
- Telogen Phase
The telogen phase, also known as the resting phase, marks the period in which the hair shaft rest in the follicle and eventually is shed from the skin. Once the hair shaft is shed, the hair follicle begins to reform, preparing for a new hair shaft to develop and the cycle start over with anagen phase. The telogen phase is the final stage of the hair cycle and typically last from 2-3 months.
Now that we have discussed the basic concepts of hair formation and characteristics, we are ready to discuss the concept of hair loss and the treatment options currently available. Stay tuned for the next two articles to be published.
Photo Credit: heartbowsmakeup.com, hairloss.org, hairsite.com, higheredbcs.wiley.com
- Bolognia J, Jorizzo JL, Schaffer JV (2012). Dermatology. Philadelphia: Elsevier Saunders. Taken from Ch 68 Biology of Hair and Nails
- Burkitt, H. George., Barbara Young, John W. Heath, and Paul R Wheater. Wheater’s Functional Histology: A Text and Colour Atlas. 3rd ed. Edinburgh ; New York: Churchill Livinstone, 1993.
- Picardo M, Ottaviani M, Camera E, Mastrofrancesco A. Sebaceous gland lipids.Dermato-endocrinology. 2009;1(2):68-71.
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