Alopecia is a medical term that describes hair loss, which can occur on any part of the head or body. It is not a single disease but rather a symptom arising from various underlying causes. Understanding these origins helps explain diverse hair loss experiences.
The Body’s Own Attack: Autoimmune Alopecia
Alopecia areata is an autoimmune response. In this condition, the body’s immune system mistakenly attacks healthy hair follicles. This malfunction leads to inflammation around the hair follicles.
Immune cells, such as T lymphocytes, infiltrate the hair bulb and disrupt the hair growth cycle. This inflammatory process causes the affected hair follicles to prematurely enter a resting phase, leading to hair shedding. Hair loss in alopecia areata often appears as round or oval patches, but it can affect any hair-bearing area, including the scalp, beard, eyebrows, or eyelashes. The follicles themselves are not permanently destroyed, meaning regrowth is often possible.
Hormonal and Genetic Influences
Androgenetic alopecia, known as male or female pattern baldness, is the most common form of hair loss, significantly influenced by genetics and hormones. This condition occurs when hair follicles have an inherited sensitivity to androgens, a group of hormones. The primary hormone involved is dihydrotestosterone (DHT), a potent derivative of testosterone.
When DHT binds to androgen receptors in genetically susceptible hair follicles, it triggers miniaturization. This process shortens the anagen, or growth phase, of the hair cycle. As a result, each new hair becomes progressively thinner, shorter, and lighter in color over time, eventually becoming fine, almost invisible. The genetic predisposition determines who will experience this type of hair loss and its pattern.
Temporary Shedding and External Factors
Hair loss can also occur due to temporary shedding, often triggered by significant physical or emotional stress, known as telogen effluvium. Various events such as major illness, surgery, rapid weight loss, certain medications, or nutritional deficiencies can trigger this. These stressors can prematurely push growing hairs (anagen phase) into the resting (telogen) phase of the hair cycle. Noticeable hair shedding typically begins two to four months after the triggering event. This type of hair loss is generally temporary, and hair usually regrows once the underlying cause is resolved.
Another cause of hair loss stems from physical stress on hair follicles, termed traction alopecia. This occurs from chronic pulling or tension on the hair, often due to tight hairstyles like braids, ponytails, or hair extensions. The constant tension damages the hair follicles over time, leading to thinning and hair loss. While initially reversible, prolonged pulling can lead to permanent damage and scarring of the hair follicles, preventing hair regrowth.