Androgenetic Alopecia accounts for over 95% of hair loss cases and is a common, hereditary condition. Prediction relies on understanding the genetic risk inherited from family members and recognizing the earliest physical changes in the hair itself. This condition involves a progressive miniaturization of hair follicles that eventually stops producing visible hair.
Genetic Predisposition
The most significant factor determining permanent hair loss is the inherited sensitivity of hair follicles to Dihydrotestosterone (DHT). DHT is synthesized from testosterone by the enzyme 5-alpha reductase. In genetically predisposed individuals, DHT triggers a process that shortens the hair’s growth phase, causing follicles to shrink over time. The resulting hair strands become progressively shorter, finer, and lighter in color.
Androgenetic Alopecia is considered a polygenic trait, influenced by multiple genes inherited from both parents. A strong connection exists with the Androgen Receptor (AR) gene, located on the X chromosome, which males inherit solely from their mother. This explains the belief that baldness is inherited primarily from the maternal grandfather.
Recent research confirms that numerous other genes on non-sex chromosomes (autosomes) contribute significantly to the timing and severity of hair loss. Genetic contributions from both the father’s and mother’s side of the family are relevant when assessing risk. Looking at the hair patterns of parents, grandparents, and siblings on both sides offers the most comprehensive prediction of genetic predisposition. Twin studies estimate the heritability of pattern baldness to be approximately 81%.
Observable Patterns of Hair Loss
The earliest warning signs of pattern baldness are subtle changes in the hair’s structure and density, not sudden, large amounts of hair loss. This condition is characterized by follicular miniaturization, where the hair follicle shrinks with each successive growth cycle. The resulting hair becomes less dense, and the scalp becomes more visible over time.
In men, hair loss typically follows a specific pattern categorized using the Norwood scale. It often starts with a receding hairline that progresses into an “M” shape at the temples. Thinning at the crown (vertex) is another common starting point, which may later merge with the receding hairline. An early indicator is a noticeable change in hair texture, where terminal hairs are replaced by wispy vellus hairs.
Female pattern hair loss, classified by the Ludwig scale, presents differently. It usually involves diffuse thinning across the top of the scalp while the frontal hairline remains preserved. A common early sign is a widening of the central hair part, making the scalp increasingly visible. True pattern baldness is defined by the quality and diameter of the hair that regrows, which progressively diminishes.
External Factors That Affect Hair Loss
While genetic sensitivity to DHT is the primary driver of permanent pattern baldness, external factors can influence its progression or cause temporary shedding. The most common temporary form is Telogen Effluvium, a reaction to a systemic shock. This shock prematurely pushes a large number of growing hairs into the resting phase, resulting in noticeable hair loss two to four months after the triggering event.
Triggers for Telogen Effluvium include severe physiological stressors such as high fever, major surgery, or rapid weight loss from crash dieting. Nutritional deficiencies, particularly low iron (ferritin), protein, or Vitamin D levels, can also disrupt the hair growth cycle. Chronic, high-level psychological stress can similarly accelerate the shedding process.
Certain medications, including some beta-blockers, retinoids, and antidepressants, are known to cause temporary hair shedding. These external factors do not permanently miniaturize the hair follicle like Androgenetic Alopecia. Instead, they cause a temporary, diffuse thinning that typically resolves once the underlying cause is corrected.