Androgenetic alopecia, or pattern baldness, is the most common form of hair loss, characterized by gradual hair thinning. While its development involves a complex interplay of factors, a strong genetic predisposition underpins its occurrence.
The Key Gene Behind Hair Loss
Androgenetic alopecia is closely linked to how hair follicles respond to androgens, which are male hormones. The Androgen Receptor (AR) gene, located on the X chromosome, provides instructions for creating androgen receptors in hair follicle cells. These receptors bind to androgens, such as dihydrotestosterone (DHT), a form of testosterone.
Variations within the AR gene can lead to androgen receptors that are more sensitive to DHT or are present in higher numbers in the scalp. When DHT binds to these receptors, it triggers miniaturization, causing hair follicles to shrink and produce progressively finer hairs until they stop growing. While the AR gene is a major determinant, especially for early-onset baldness, androgenetic alopecia is a polygenic trait, meaning multiple genes contribute to its expression and severity.
How Baldness Genes Are Inherited
Inheritance of baldness genes is more complex than commonly believed, involving contributions from both parents. The strong association with the X-linked AR gene explains why baldness often appears to come from the mother’s side; males inherit their single X chromosome directly from her, passing on any AR gene variants. This can significantly influence a man’s susceptibility to pattern baldness.
However, androgenetic alopecia is not determined by a single gene; it is a polygenic condition influenced by multiple genes from both parents. While the X-linked AR gene plays a significant role, other genes from either parent can affect the likelihood, pattern, and age of onset. Therefore, assessing risk involves considering family history on both maternal and paternal sides.
Other Influences on Hair Thinning
While genetics primarily determine susceptibility, various non-genetic factors can also contribute to hair thinning or loss. Chronic or severe stress can impact hair health, pushing many hair follicles prematurely into a resting phase and leading to increased shedding (telogen effluvium). This hair loss is temporary, with regrowth occurring once the stressor is managed.
Lack of essential vitamins and minerals like iron, zinc, vitamin D, and B vitamins can affect hair growth and lead to shedding. Certain medical conditions, including thyroid disorders, can cause diffuse hair loss. Some medications, such as those for high blood pressure or depression, and specific lifestyle choices can also contribute to hair thinning.
Male Versus Female Hair Loss Patterns
Androgenetic alopecia manifests with different patterns in men and women, primarily due to hormonal differences. In men, hair loss typically begins with a receding hairline and thinning at the crown. This can progress to partial or extensive baldness, leaving a horseshoe-shaped pattern of hair around the sides and back.
Female pattern hair loss presents as diffuse thinning across the central scalp, often with a widening hair part. The frontal hairline is typically preserved, and total baldness is rare. These differing patterns are influenced by the balance of hormones like testosterone and estrogen, which modulate gene expression in hair follicles.