What Happened to Grandpa’s Hair: An Explanation of Male Pattern Hair Loss

/ lionstalkscience

By Sarah G Latario

Have you ever wondered why men bald differently than women? While hair loss does not exclusively affect people with an X and Y chromosome, male pattern baldness, also known as androgenetic alopecia (AA), affects over 50% of men by age 50. The characteristic pattern of hair loss associated with AA begins with thinning of hair around the temples that gradually recedes backward towards the crown of the head where similar thinning is also occurring. These regions of hair loss eventually merge, causing baldness at the top of the scalp and leaving hair along the ears and back of the head.

Hair loss is fundamentally caused by a shift in the ratio of time each hair follicle spends in its growth vs resting phase. Hair follicles cycle through four main stages: the anagen, catagen, telogen, and exogen phases (Figure 1). The anagen phase is where hair growth occurs, with most hair follicles of the scalp in this stage for 2-8 years.1 During the anagen phase, the hair follicle forms and grows the hair shaft, which is what we usually refer to as “hair”. The length of hair naturally, if left uncut, directly reflects the length of the anagen phase for each individual hair strand. The length of time spent in the anagen phase declines with age, causing thinner, weaker hair in older individuals.2 The catagen phase is a transitionary stage where the hair follicle releases from its anchor in the deeper tissue below the skin. This process takes about two weeks.1,3 The telogen phase follows and is considered the resting stage, lasting 2-3 months.1 While the old hair rests, new hair begins to form at the base of the hair follicle below the old hair. This new hair eventually pushes the old hair out and causes it to be shed in the exogen phase.1 Each hair follicle independently cycles through these four phases, with about 100-150 hairs shed each day from the scalp of healthy individuals during the exogen phase.4 Noticeable hair loss, such as the kind seen in AA is caused by a shift in the balance of these phases with more hair follicles residing in the telogen phase and fewer in the anagen phase.

Figure 1. Phases of the hair growth cycle. The hair growth cycle is made up of four phases, anagen, catagen, telogen, and exogen.

Many different hormones are involved in regulating the balance of these phases and ultimately hair growth and loss. A form of testosterone, dihydrotestosterone (DHT), is the most involved in AA. During puberty, DHT acts to increase the size of hair follicles in specific body hair regions that are sensitive to this hormone such as the beard.5 However, in later years of life, DHT also causes miniaturization of hair follicles in other regions of the body, such as the crown of the head in AA (Figure 2).5 Miniaturization is the process by which hairs transition from terminal hairs (thicker, pigmented hair) to vellus hairs (thinner, unpigmented hair like “peach fuzz”). Even in what are considered “bald” regions of the scalp, hair follicles are still present and cycling.5 The hair, itself, is shrinking and undergoing miniaturization during the balding process. Individuals have different levels of not only DHT, but also enzymes that create it and break it down. Genetics play a large role in the balance of these enzymes and hormone levels. Due to these variations, not everyone loses hair at the same age or rate.

Figure 2. The process of hair miniaturization [6]. As DHT acts on the hair follicles, the hair thins and grows shorter, spending less time in the anagen phase.

 Male pattern hair loss is a complex process controlled by multiple genes and hormones. There are multiple ways to manage hair loss with most focused on decreasing DHT, maintaining hair follicles in the anagen phase, and preventing them from shifting to the telogen phase.1,2 Ultimately, treatment is not needed unless desired. Male pattern baldness is a natural and common part of the aging process for men and is not something to worry about.

TL;DR

  • Male pattern balding (androgenetic alopecia, AA) is the progressive loss of hair along the temples and crown of the head.
  • Hair growth occurs in 4 phases with hair loss being seen when each hair spends less time in the growth phase.
  • In AA, a form of testosterone causes sensitive hair follicles to spend less time in the growth phase. This causes the hair to thin and baldness to occur.

Reference

  1. Natarelli N, Gahoonia N, Sivamani RK. Integrative and Mechanistic Approach to the Hair Growth Cycle and Hair Loss. J Clin Med. 2023 Jan 23;12(3):893. doi: 10.3390/jcm12030893. PMID: 36769541; PMCID: PMC9917549.
  2. Millar SE. Molecular mechanisms regulating hair follicle development. J Invest Dermatol. 2002 Feb;118(2):216-25. doi: 10.1046/j.0022-202x.2001.01670.x. PMID: 11841536.
  3. Alonso L, Fuchs E. The hair cycle. J Cell Sci. 2006 Feb 1;119(Pt 3):391-3. doi: 10.1242/jcs.02793. PMID: 16443746.
  4. Harrison S, Bergfeld W. Diffuse hair loss: its triggers and management. Cleve Clin J Med. 2009 Jun;76(6):361-7. doi: 10.3949/ccjm.76a.08080. PMID: 19487557.
  5. Paus R, Cotsarelis G. The biology of hair follicles. N Engl J Med. 1999 Aug 12;341(7):491-7. doi: 10.1056/NEJM199908123410706. PMID: 10441606.
  6. Paiva-Santos, Ana Cláudia & Pereira-Silva, Miguel & Guerra, Catarina & Costa, Diana & Peixoto, Diana & Pereira, Irina & Pita, Inês & Ribeiro, António & Veiga, Francisco. (2020). Topical Minoxidil-Loaded Nanotechnology Strategies for Alopecia. Cosmetics. 7. 21. 10.3390/cosmetics7020021.

Leave a comment