It is believed that in follicles with a genetic predisposition for hair loss, a hormone called DHT (dihydrotestosterone) causes the growth phase of the hair cycle to become increasingly shorter. This shorter growth window produces hair strands that are shorter in length and increasingly thinner in diameter with each hair cycle. For those without AGA in their genes, DHT is not a threat to triggering pattern hair loss. Although it is medically benign, androgenetic alopecia can get progressively worse if left untreated.
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HOW DOES HAIR LOSS OCCUR?
Understand the hair growth cycle, identify the various types of hair loss, and learn about the different types of treatment options.
How Hair Loss Occurs in Androgenetic Alopecia
How Does Hair Loss Occur in AGA?
Androgenetic alopecia is defined as hair loss that is due to an androgen hormone which inhibits the process of the healthy hair cycle and leads to shorter hair cycles which produce progressively shorter and thinner strands of hair. This type of hair loss - also referred to as male & female pattern balding - can be easily identified as it occurs in very predictable patterns in men and women. Hair loss in androgenetic alopecia occurs through the natural process of miniaturization.
Miniaturization - The Root Cause of Pattern Hair Loss
Miniaturization is the progressive deterioration of a hair follicle. A healthy hair follicle is capable of producing healthy, terminal hair which is thicker and darker in appearance. Over time the follicle shrinks with each cycle of hair and is no longer capable of producing healthy terminal hairs; instead it produces thinner, weaker strands of hair, referred to as vellus hair. Eventually a miniaturized follicle dies and ceases to produce hair altogether, resulting in balding.
According to the Hair Transplant Forum International by the International Society of Hair Restoration Surgery, “Scalp follicles exist as compound follicular units. In early stages of hair loss, the arrector pili muscle remains attached to the primary follicle, but loses its attachment to some of the regressing secondary follicles in some follicular units. Miniaturization of secondary follicles and detachment of the APM from these follicles extends to the rest of the follicular units. At this stage, patients may complain of hair thinning and loss of volume in their ponytail without any visible baldness. With further progression, miniaturization continues and the muscle loses attachment to the secondary follicles in affected follicular units completely. Primary follicles eventually miniaturize and this leads to visible baldness. When primary follicles lose muscle attachment, the hair loss becomes irreversible.” [i]
What Causes Miniaturization of Hair?
The Hair Growth Cycle: How Hair Grows
Hair is made up of proteins called keratins, and it grows from follicles underneath the skin. Although every strand of hair on the human body goes through the hair growth cycle, each hair grows independently of the other. The hair growth cycle occurs in three main phases: the Anagen (growing) phase, which lasts 2 to 6 years, is when the hair is firmly attached to the hair root; the Catagen (transitional) phase lasts a few days and is when the hair stops growing and forms the basis for the next hair; and the Telogen (resting) phase which lasts 3 to 4 months and is when the hair sheds and causes the stem cells to move deeper in the dermis to start a new anagen phase. People are born with approximately 5 million follicles on their body, and about 100,000 follicles on just the scalp. Regardless of where the hair is located on the body, all hairs undergo a similar growth cycle.
The Growth Cycle of Hair
The hair growth cycle consists of 3 stages. Ninety percent of the hair on your scalp is either in the anagen or catagen phase at any one time. No more than ten percent is usually in the telogen phase at any given time.
Anagen Phase: The first of the three stages is the anagen phase. This is also called the growth stage. In this stage of the hair cycle, the hair shaft is actively growing inside the follicle, with rapidly dividing new cells being supplied by the dermal papilla. This stage typically lasts between 2 and 6 years.
Catagen Phase: The second of three stages of hair growth is called the catagen phase. This is also called the degradation phase and is a transitional phase where the hair follicle pulls away from the dermal papilla. Since the hair follicle is no longer being supplied with the new cells from the dermal papilla, the hair stops growing. This stage is brief, usually lasting several days.
Telogen Phase: The last of the three stages is called the telogen phase. This is also known as the resting phase. During this stage, the hair follicle remains inactive and the hair shaft usually stays in place until the follicle cycles back to the anagen phase where the new hair shaft emerges and pushes out the old one. This lasts about 3-4 months.