Androgenetic alopecia, known as male or female pattern baldness, is a common form of hair loss characterized by a predictable pattern of thinning and loss. While various factors influence hair health, genetics significantly determine an individual’s susceptibility.
The Main Genetic Driver
The Androgen Receptor (AR) gene is a primary genetic factor linked to hereditary baldness. Located on the X chromosome, inherited by men from their mothers, variations in this gene can make androgen receptors more sensitive to hormones. This increases hair loss likelihood and often leads to the belief that baldness is inherited solely from the mother’s side.
While the maternal lineage contributes to baldness inheritance via the AR gene, this is an incomplete picture. Studies show certain AR gene variations more than double the risk of male pattern baldness. However, the AR gene is not the only genetic influence on hair loss.
A More Complex Inheritance
Baldness is a polygenic condition, meaning multiple genes contribute to an individual’s predisposition, not just one. Beyond the AR gene, numerous other genes on various chromosomes, inherited from both parents, play a role in androgenetic alopecia. A 2017 review identified 63 genes influencing male pattern baldness, with only six on the X chromosome. Genes like SRD5A2, involved in converting testosterone to DHT, and PTGFR, related to prostaglandin signaling, are also linked to baldness progression.
This polygenic nature means both maternal and paternal genetic contributions are important for baldness risk. While the mother’s AR gene has a notable impact, genes from the father’s side also significantly influence hair loss likelihood and severity. The interaction of these genes creates a complex inheritance pattern, allowing baldness to manifest differently even among siblings.
Hormones and Hair Loss
Genetic predisposition leads to hair loss through hormones, particularly androgens like dihydrotestosterone (DHT). In individuals with genetically sensitive hair follicles, DHT binds to androgen receptors, triggering follicular miniaturization. This causes hair follicles to shrink over time, producing progressively thinner, shorter, and less pigmented hairs.
DHT forms when the enzyme 5-alpha reductase converts testosterone into this more potent androgen. When DHT binds to sensitive hair follicles, it shortens the anagen (growth) phase and extends the telogen (resting) phase. Eventually, these miniaturized follicles may cease to produce hair, leading to visible baldness. A follicle’s sensitivity to DHT is largely determined by genetics.
Interpreting Your Family History
Understanding family history offers insights into one’s baldness risk, but requires looking beyond just one side of the family. Since baldness is a polygenic trait with contributions from both parents, examining hair loss patterns in both maternal and paternal relatives provides a more comprehensive view. If many men on both sides of the family experience hair loss, an individual’s risk increases.
While genetics provide a strong indication of predisposition, they do not guarantee a specific outcome. The exact pattern and onset of hair loss can vary due to the complex interplay of multiple genes and other factors. Baldness can sometimes skip generations or affect siblings differently, highlighting the nuanced nature of its inheritance.