# The Role of DHT and Androgen Receptors in Hair Follicle Miniaturization
Androgenetic Alopecia (AGA) is the most common type of hair loss, affecting hundreds of millions of men and some women worldwide. Its core pathological process is “hair follicle miniaturization” — the gradual thinning, shortening, and lightening of thick, dark terminal hairs until they become nearly invisible vellus hairs. This process is closely related to two key substances in the body: dihydrotestosterone (DHT) and the androgen receptor (AR).
Let us first understand DHT. DHT is a “potent” metabolite of testosterone, produced when testosterone is converted by 5α-reductase (an enzyme found in tissues such as the skin, scalp, and prostate). DHT has approximately five times the androgenic activity of testosterone, meaning it binds more strongly to androgen receptors and produces a more sustained effect. In the scalp hair follicles, DHT is the primary driver of hair follicle miniaturization.
The androgen receptor (AR) is a protein present in the dermal papilla cells of hair follicles. The dermal papilla acts as the “command center” of the hair follicle, regulating its growth cycle and size. When DHT binds to AR, the resulting complex enters the cell nucleus, binds to specific regions of DNA, and alters the expression of a series of genes. Among these genes, some promote the shortening of the anagen (growth) phase, while others accelerate the onset of the catagen (regression) and telogen (resting) phases.
The normal life cycle of a hair follicle includes the anagen phase (approximately 2–6 years), catagen phase (approximately 2–3 weeks), and telogen phase (approximately 3–4 months). Under the persistent influence of the DHT-AR complex, the anagen phase is significantly shortened, causing the follicle to prematurely enter the catagen and telogen phases. The newly grown hair is thinner and shorter than the previous cycle. With each such cycle, the hair follicle shrinks further until it is fully miniaturized.
Scientific research has confirmed that the DHT-AR complex activates multiple signaling pathways, such as promoting the release of transforming growth factor-beta (TGF-β). TGF-β can induce apoptosis of dermal papilla cells and inhibit the proliferation of hair follicle epithelial stem cells. At the same time, DHT reduces the production of vascular endothelial growth factor (VEGF) in the hair follicle, leading to insufficient blood supply and further accelerating atrophy.
It is worth noting that not all scalp hair follicles are sensitive to DHT. The typical pattern of androgenetic alopecia — hair loss at the forehead, vertex, and crown — occurs precisely because the hair follicles in these areas have a greater number and higher activity of androgen receptors. Hair follicles at the occipital and temporal regions are much less sensitive to DHT, which is why hair follicles harvested from these areas for transplantation can survive long-term.
Genetic factors play a key role in the sensitivity of hair follicles to DHT. Studies have shown that the length of the CAG repeat sequence on the androgen receptor gene (AR gene) is associated with the risk of hair loss. Shorter CAG repeats result in higher androgen receptor activity, increasing the sensitivity of hair follicles to DHT. In addition, the expression level of 5α-reductase is also genetically regulated; some individuals naturally have higher 5α-reductase activity in the scalp, thereby producing more DHT.
It must be emphasized that DHT is not a “harmful substance.” It plays normal physiological roles in male embryonic development, the formation of secondary sexual characteristics during puberty, spermatogenesis, and female body hair growth. The miniaturization process is triggered only when hair follicles in specific scalp regions of genetically predisposed individuals are chronically exposed to high concentrations of DHT.
Currently, there are two main treatment strategies targeting the DHT-AR pathway: one is to inhibit the activity of 5α-reductase (e.g., finasteride) to reduce DHT production; the other is to directly block the binding of DHT to the androgen receptor (e.g., certain AR antagonists). Additionally, medications such as minoxidil work by improving blood supply to the hair follicle and prolonging the anagen phase. However, these treatments must be administered under medical supervision, and their effectiveness varies among individuals. They cannot reverse hair follicles that have already undergone complete miniaturization.
Understanding the interaction between DHT and the androgen receptor is the foundation for a scientific understanding of androgenetic alopecia. Research into this mechanism continues to advance, and more precise intervention methods may become available in the future. Nevertheless, hair loss is a complex, multifactorial process influenced by genetics, hormones, age, environment, and other factors.
**For reference only, and does not constitute medical advice.** If you are experiencing hair loss, it is recommended to consult a dermatologist for a professional evaluation and individualized treatment.