Understanding the Triggers of Hair Loss

Hair loss, often a source of concern for many, can stem from a variety of causes. The phenomenon known as alopecia encompasses multiple forms, each with distinct triggers and characteristics.

Human beings typically have between 80,000 and 100,000 hairs on their scalp. These hairs grow from follicles located in the dermis and undergo a life cycle that includes growth (anagen phase), transition (catagen phase), and rest (telogen phase). During a normal cycle, approximately 88 to 90 percent of hair is in the growth phase, which lasts between two to seven years, with hair growing about 0.3 mm per day. The subsequent catagen phase is a brief transition lasting two to four weeks, followed by a resting phase where hair remains dormant for two to four months before eventually falling out.

On average, it is normal for individuals to lose 50 to 100 strands of hair daily. These strands, which grow independently, can be synchronized by factors such as hormonal changes, medications, and even seasonal variations.

Excessive hair loss is classified as effluvium, which can affect not only the scalp but also facial hair and body hair. Two primary types include anagen effluvium, where hair in the growth phase is lost, and telogen effluvium, where hair prematurely shifts to the resting phase, resulting in significant shedding.

Alopecia serves as a collective term for various forms of hair loss, including scarring (irreversible) and non-scarring (reversible) types. Common non-scarring forms include alopecia areata, characterized by patchy hair loss, and androgenetic alopecia, known for a more diffuse thinning of hair. Both anagen and telogen effluvium are also included in this category, often triggered by stress.

On the other hand, irreversible forms of alopecia involve conditions such as lichen planopilaris, folliculitis decalvans, and frontal fibrosing alopecia, which can affect eyebrows as well. These forms are often characterized by inflammation that leads to permanent damage to hair follicles.

Alopecia's various manifestations can result from a combination of factors. For instance, androgenetic alopecia is largely influenced by genetic predisposition to sensitivity to dihydrotestosterone (DHT). In contrast, alopecia areata is an autoimmune disorder in which the immune system mistakenly attacks hair follicles.

Other forms, such as anagen and telogen effluvium, frequently arise from metabolic or psychological stress, including illness, medication (such as biologics and chemotherapy), heavy metal exposure, or hormonal fluctuations, such as those occurring during pregnancy.

Scarring alopecias, however, are marked by inflammatory processes that cause permanent damage to hair follicles, often replaced by scar tissue. Causes for such irreversible conditions can include burns, severe infections, trauma, or radiation treatments.

The diagnosis and management of these diverse conditions can be complex. While a few treatments have been approved for use, many others are often promoted without substantial evidence supporting their effectiveness.

Additionally, some individuals may experience hair loss due to trichotillomania, a psychological disorder characterized by the compulsive pulling of hair, which can affect hair from the scalp, eyebrows, and even eyelashes.