Androgenetic alopecia, or male/female pattern hair loss, is the most common form of progressive hair loss, affecting millions globally. While other factors influence hair health, genetics is the primary driver. Twin studies suggest inherited factors account for up to 80% of cases. This article explores the genetic basis of balding and how inherited traits influence hair follicles.
The Principal Genetic Link: The Androgen Receptor Gene
The primary genetic factor associated with androgenetic alopecia is the Androgen Receptor (AR) gene. Located on the X chromosome, which men inherit from their mothers, the AR gene explains why baldness often appears to come from the mother’s side. The AR gene provides instructions for androgen receptors, proteins in hair follicles that respond to male hormones. Variations in the AR gene can make androgen receptors more sensitive to these hormones, causing hair follicles to react more strongly to normal androgen levels. While the AR gene is a significant contributor, it is not the sole genetic determinant for balding.
The Role of Other Genes and Polygenic Inheritance
Androgenetic alopecia results from a complex interplay of multiple genes, known as polygenic inheritance, rather than a single gene. Beyond the AR gene, numerous other genes on various chromosomes contribute to hair loss predisposition and severity. These genes influence hair follicle development, inflammatory responses, and the scalp’s hormonal environment.
Research points to gene variants on chromosomes like 20p11 and 2q35 that impact hair growth pathways. The combination and interaction of these genetic factors determine an individual’s susceptibility and how hair loss manifests. This complex genetic background explains why balding patterns and progression vary significantly among individuals, even within families.
How Genes Lead to Hair Loss: Hormonal Interaction
Genetic predispositions directly influence how hair follicles respond to hormones, particularly dihydrotestosterone (DHT). DHT is an androgen, a male sex hormone produced from testosterone by the enzyme 5-alpha reductase. Genetically susceptible hair follicles, largely due to AR gene variations and other contributing genes, exhibit increased DHT sensitivity.
When DHT binds to these sensitive receptors, it triggers follicular miniaturization. This process causes hair follicles to gradually shrink, shortening the anagen (growth) phase of the hair cycle. Over time, hairs become progressively thinner, shorter, and finer, eventually resembling vellus hairs until they cease growing. This miniaturization is the mechanism underlying visible thinning and hair loss in androgenetic alopecia.
The Influence of Non-Genetic Factors
While genetics are the primary determinant of androgenetic alopecia, other factors can influence its onset or progression. Stress can contribute to hair loss, though it often plays a secondary role to genetic susceptibility. Dietary deficiencies, such as iron, zinc, biotin, or protein, can impact hair health and exacerbate thinning.
Certain medications, including those used in chemotherapy, anticoagulants, or antidepressants, have been linked to hair loss as a side effect. Hormonal imbalances, beyond androgen-related ones, such as thyroid issues, can affect hair growth. Lifestyle choices like smoking have been associated with increased risk or severity of hair loss, possibly by affecting hormone levels or inducing oxidative stress.