What is Pattern Hair Loss?

Humans hold the mammalian distinction of being the only species to experience androgenetic alopecia (AGA) also known as common pattern hair loss. The term common pattern hair loss is used because more than 95% of those suffering hair loss are affected by AGA. Thirty percent of men in their thirties are losing hair, forty percent in their forties and so on.

Women also lose hair due to AGA. However, in women, the juvenile anterior hair line is usually retained with diffuse thinning across the top and back of the scalp. In men, bilateral recession of the anterior temples is often the first sign of AGA. A bald spot may form in the posterior crown. In advanced affected males, the bald spot and thinning temples may meet leaving a thin fringe of hair above the ears and in the back of the scalp as the only region left producing hair.

From a research perspective the fact that only humans are susceptible creates a daunting challenge because there is no animal model for pattern hair loss readily available to study. Interestingly, the term "hair loss" is a misnomer because the hair is not so much lost as miniaturized. Even in profoundly affected individuals where the scalp is essentially denuded of hair, tiny vellus (non-pigmented & baby fine) hairs can be observed. In the hair follicle, the process of miniaturization occurs as well. The key anatomical structures are preserved, but they are rendered much smaller than they were when the follicle produced pigmented full caliber hair.

AGA has long been understood to be genetically-mediated. One or both parents may contribute hair loss susceptibility. Very few AGA genes have been cloned to date, although work continues to unlock the genetic basis of the disease. From an epigenetic standpoint, circulating hormones play a pivotal role in the onset and progression of AGA. The principle metabolite of testosterone (T) is dihydrotestosterone (DHT). DHT is metabolized from T through the action of the enzyme 5 alpha-reductase (5AR). You can think of DHT as the gasoline that burns the hair and 5AR as the match that sets the gasoline alight.

Recently, investigators in our lab and elsewhere have begun to demonstrate additional factors as contributory to AGA. Among these factors, one of the most important is inflammation. Published research has shown that inflammation of the hair follicle is a noted hallmark of AGA. There may well be a negative synergy at work in which DHT and inflammation contribute to cause a more accelerated and widespread degree of loss than would otherwise occur, if inflammatory cytokines were not causing damage to the follicle.