At some point in their lives, all men experience hair thinning and hair loss. Hormones, genetics, and age each play a critical role in when the loss occurs and how extensive it will be.
Hair thinning or “miniaturization” is the first stage of hair loss. All hair growth depends on the proper functioning of the hair’s follicle. In normal circumstances, the follicle moves through a cycle that includes a growing (or anagen) phase and a resting (or telogen) phase, each of a specific duration. When miniaturization occurs, the length of the resting phase increases. Because the resting phase has been longer, the shaft of the new hair that later emerges is narrower. With each subsequent cycle, the resting phase gets progressively longer, and the resulting hair progressively narrower/thinner, until the follicle eventually stops functioning and a hair no longer grows.
But why does miniaturization affect some hair follicles and not others? And why do some men experience it beginning in their twenties while others only see the first evidence of the problem in their seventies? The answer is a complex interaction between the male hormone dihydrotestosterone (DHT), inherited genes, and age.
Scientists have determined that the male hormone dihydrotestosterone (DHT) is responsible for hair loss due to the way it interacts with the cells that make up the hair follicle. This DHT interaction causes the cells to increase the resting (telogen) phase in the hair-growth cycle, leading to hair miniaturization and the eventual cessation of hair growth described above. However, all hair follicle cells are not susceptible to the effects of DHT to the same degree. This is why in the majority of cases, the areas where future hair loss is most likely to occur, i.e. the “pattern,” can be predicted. The terms male pattern baldness, male pattern alopecia, androgenetic alopecia, adrogenic alopecia, and alopecia androgenetica all refer to this condition, which is the most common form of hair loss in men.
In male pattern baldness, the hair follicles most susceptible to the effects of DHT are located in the front area of the scalp above the temples (the typical “receding hairline”), so this is where hair loss first occurs. Over time, the follicles that make up the back, crown area also begin to show the effects. Gradually, these two areas of thinning and hair loss meet in the middle until all hair is lost on the scalp. The hair follicles on the sides of the head are the least susceptible to the effects of DHT, although with aging some of them will also thin. The Norwood Classification system has been developed as a universal way to identify a man’s stage of hair loss. The Norwood Classification system divides the progression of hair loss into seven stages. The “Type A” variant in Norwood Classification describes an alternate, slightly less common pattern where the hair follicles are affected across the entire hairline at the front of the scalp and the hair thinning and loss proceeds in a line backward toward the crown.
The reason why certain hair follicles are susceptible to the effects of the DHT hormone and a man experiences the typical Norwood Classification pattern of hair loss, or the Type A variant, or merely overall hair thinning and hair loss as he ages, is determined by the genes he inherited from his parents. While the common belief that “baldness is inherited from the mother’s side” is not entirely true, research shows that hair loss on the mother’s side can be a slightly more important predictor in whether or not a man experiences the same patterns of hair loss. Although there is still much to be learned regarding the genetic link to male pattern baldness, scientists do believe the trait is dominant, meaning it only needs to be passed down by one of the two parents to express itself. However, when exactly that expression occurs-and hair thinning and loss is seen-is determined by outside factors, most importantly hormones and age.
The male hormone testosterone is produced by the testicles and is responsible for the development of male sexual characteristics during puberty. The hormone dihydrotestosterone (DHT) is not the same as testosterone itself, but is formed when the enzyme “5-Alpha reductase” acts upon testosterone. The areas of the scalp where hair loss occurs show more of this “5-Alpha reductase” enzyme activity, leading to higher levels of DHT production. The DHT then binds to hair follicle cells causing miniaturization and hair loss as described in previous paragraphs. However, this effect is not seen immediately. Age is also an important factor.
While the necessary hormones and the genetically vulnerable hair follicles must be present to cause hair loss, the third critical component is the duration of the hormone exposure on the follicle. Even with a genetic disposition toward DHT vulnerability, some hair follicles will withstand the effects of DHT for many decades, while others will stop functioning within a few years. Eventually, all hair follicles, even those with no genetic predisposition, will succumb to the effects of the presence of DHT, which is why all men in their seventies and eighties will show some signs of hair thinning and hair loss. Still, all of these processes are not clear-cut. Researchers can see that hair loss in men does not occur at a regular pace, but rather in cyclical patterns that include periods of rapid hair loss followed by periods of much slower hair loss and relative stability. What triggers the changes in these cycles has yet to be fully understood.
While there are still many mysteries surrounding male pattern baldness, the scientific community and medical profession have made great strides in developing non-surgical approaches to help minimize the early effects of DHT on the hair follicle and cutting-edge surgical techniques, such as FUE, Follicular Unit Extraction, and FUT, Follicular Unit Transplantation, performed by Dr. Rawnsley, to restore hair to the areas where the hair follicles no longer function.