The belief that a man’s balding pattern is determined by his mother’s father is a piece of long-standing folklore. Modern science reveals a more intricate picture. Male pattern baldness, or Androgenic Alopecia, is the most frequent form of progressive hair loss, characterized by a receding hairline and thinning crown. Genetics are the primary cause, contributing to a heritability of over 80%. However, the process is not controlled by a single gene or a single side of the family. Androgenic Alopecia is a polygenic trait, influenced by the cumulative effect of multiple genes inherited from both parents.
The Strongest Genetic Link: The X Chromosome
The popular belief about the maternal grandfather holds truth because the single most influential gene identified in male pattern baldness is located on the X chromosome. A male inherits this chromosome exclusively from his mother, heavily weighting the maternal side of the family. The X chromosome carries the Androgen Receptor (\(AR\)) gene, considered the strongest single genetic predictor for the condition.
The \(AR\) gene provides instructions for making the androgen receptor, a protein in hair follicle cells that interacts with male sex hormones called androgens. Dihydrotestosterone (DHT), a potent derivative of testosterone, is the direct cause of pattern hair loss. Variations in the \(AR\) gene can lead to receptors that are hypersensitive to DHT, triggering follicular miniaturization.
This sensitivity causes hair follicles to shrink over time, resulting in shorter, finer, and eventually nonexistent hairs. Since a male receives his only X chromosome from his mother, the \(AR\) gene version he gets reflects the genes present on her X chromosomes. This explains why a man’s risk is often correlated with the hair status of his maternal grandfather, who passed that variant to the mother. The mother herself is a carrier, and her own hair loss may not be pronounced since she has a second X chromosome for compensation.
The Role of Autosomal Genes and Paternal Influence
Despite the strong influence of the X chromosome, the theory that baldness is passed down only from the mother’s side is inaccurate. Numerous genes located on non-sex chromosomes, called autosomes, also contribute to the overall risk profile. These autosomal genes are inherited from both the father and the mother, demonstrating a clear role for paternal genetics in determining the severity and onset of hair loss.
Research has identified multiple genetic locations on these autosomes that increase the risk of developing male pattern baldness. For example, a susceptibility locus found on chromosome 20 (20p11) is inherited independently of the sex chromosomes and can be passed down from either parent. When risk alleles are present at both the X-linked \(AR\) gene and the autosomal 20p11 locus, the chance of developing early-onset hair loss can increase by as much as sevenfold.
The contribution of these autosomal genes explains why a man can experience baldness even if his mother’s side has a full head of hair; his father also contributed significant risk factors. The majority of genetic risk loci for male pattern baldness are located on these autosomes. The total combination of risk-associated genes inherited from both parents determines the final outcome.
Other Factors Influencing Hair Loss
While genetics are the dominant factor in Androgenic Alopecia, hair loss can be influenced or mimicked by several non-inherited factors.
Hormonal Changes
Hormonal fluctuations outside of the DHT pathway, such as those caused by thyroid disorders (hyperthyroidism or hypothyroidism), can disrupt the normal hair growth cycle and lead to diffuse hair thinning.
Nutritional Deficiencies
Hair follicles require a steady supply of essential micronutrients. Low levels of iron, zinc, or Vitamin D can impair hair production and lead to increased shedding.
Stress and Medication
Severe physical or emotional stress can trigger Telogen Effluvium, a temporary condition where many hair follicles prematurely enter the resting phase, causing noticeable hair loss months later. Certain medications, including those for cancer, arthritis, and heart conditions, can also cause temporary hair loss.
These non-genetic causes are distinct from male pattern baldness because they result in temporary and diffuse thinning, rather than the characteristic patterned recession. Addressing these underlying factors can often reverse the hair loss, unlike the permanent nature of genetic balding.