Alopecia
Alopecia refers to hair loss from the scalp or other parts of the body, and encompasses a spectrum of disorders with diverse etiologies, clinical presentations, and prognoses. The pathogenesis of alopecia varies by type but often involves complex interactions between genetic, immunological, hormonal, and environmental factors. In autoimmune forms such as alopecia areata, an aberrant immune response targets hair follicles, leading to their premature transition to the telogen (resting) phase and subsequent hair shedding. In androgenetic alopecia, dihydrotestosterone (DHT)-mediated miniaturization of hair follicles predominates, resulting in progressive hair thinning. Other types may result from physical trauma, chemical exposures, medications, or systemic diseases. The health impacts of alopecia extend beyond physical manifestations, frequently causing significant psychological distress, reduced self-esteem, and impaired quality of life. Severe cases may be associated with social stigma and contribute to anxiety or depressive disorders, underscoring the need for comprehensive management.
Androgenetic alopecia, also known as male- or female-pattern hair loss, is the most prevalent type of hair loss, characterized by progressive thinning of the scalp hair in a defined pattern. It is driven by genetic predisposition and androgenic hormones, particularly dihydrotestosterone (DHT), which induce miniaturization of susceptible hair follicles. In men, this typically presents as bitemporal recession and vertex balding, while women experience diffuse thinning over the crown with retention of the frontal hairline.
Alopecia areata is an autoimmune disorder marked by sudden, patchy, non-scarring hair loss on the scalp or other body sites. The immune system inappropriately targets anagen hair follicles, resulting in sharply demarcated areas of hair loss. The disease course is unpredictable, with possibilities of spontaneous regrowth or progression to more extensive forms, such as alopecia totalis (total scalp hair loss) or alopecia universalis (complete body hair loss).
Telogen effluvium is characterized by diffuse hair shedding due to premature transition of hair follicles from the anagen (growth) phase to the telogen (resting) phase. It is commonly triggered by physiological or psychological stressors, such as illness, surgery, childbirth, or significant weight loss. The condition is usually self-limited, with hair regrowth occurring as the underlying cause resolves.
Traction alopecia results from chronic tension or pulling forces applied to the hair, often due to certain hairstyles (e.g., tight braids, ponytails, or extensions). Over time, this mechanical stress leads to follicular damage and localized hair loss, which may become permanent if the insult persists.
Cicatricial alopecia encompasses a group of rare disorders characterized by permanent destruction of hair follicles and replacement with fibrous tissue. Etiologies include inflammatory conditions (e.g., lichen planopilaris, discoid lupus erythematosus), infections, or physical trauma. Early diagnosis and intervention are critical to prevent irreversible hair loss.
Alopecia is a common condition affecting individuals of all ages, sexes, and ethnic backgrounds, though prevalence and clinical characteristics vary by type. Androgenetic alopecia affects up to 50% of men by age 50 and approximately 40% of women by age 70, with onset often occurring after puberty. Alopecia areata has a lifetime risk of about 2%, with no significant sex predilection, and can present at any age, though most commonly before age 30. Telogen effluvium is a frequent cause of diffuse hair loss, particularly among women, and is often associated with identifiable triggers. Traction alopecia is more prevalent in populations with cultural or personal hair practices that involve chronic tension. Cicatricial alopecias are relatively rare, accounting for less than 3% of all hair loss cases. The psychosocial burden of alopecia is substantial, with studies demonstrating increased rates of anxiety, depression, and social withdrawal among affected individuals.
The diagnosis of alopecia requires a thorough clinical evaluation, including a detailed history of hair loss onset, duration, pattern, associated symptoms, and potential triggers or exposures. Physical examination focuses on the distribution, extent, and characteristics of hair loss, as well as scalp and skin findings. Dermoscopy (trichoscopy) is a valuable non-invasive tool for visualizing hair and scalp structures, aiding in the differentiation of alopecia types. Laboratory investigations may be indicated to exclude underlying systemic diseases, such as thyroid dysfunction, nutritional deficiencies (e.g., iron, vitamin D), or autoimmune disorders. In cases of suspected cicatricial alopecia or atypical presentations, scalp biopsy with histopathological analysis is often performed to confirm diagnosis and guide management. Diagnostic criteria are tailored to each alopecia subtype, incorporating clinical, trichoscopic, and histological features. Additional tests, such as hair pull or tug tests, can help assess the activity and severity of hair shedding.
Treatment options for alopecia include several pharmacological agents with varying mechanisms of action. Ritlecitinib is an oral Janus kinase inhibitor indicated for the management of alopecia areata, targeting immune-mediated pathways implicated in follicular inflammation. Baricitinib, another oral Janus kinase inhibitor, is utilized in the treatment of alopecia areata, offering immunomodulatory effects that help reduce autoimmune-driven hair follicle damage. Dutasteride is a dual 5-alpha-reductase inhibitor prescribed for androgenetic alopecia, effectively reducing dihydrotestosterone levels and slowing the progression of hair follicle miniaturization. Finasteride, a selective 5-alpha-reductase type II inhibitor, is also indicated for androgenetic alopecia and works by decreasing scalp DHT concentrations to promote hair retention and regrowth. Minoxidil is a topical vasodilator applied directly to the scalp, approved for both male and female pattern hair loss, and functions by prolonging the anagen phase and enhancing follicular size, thereby stimulating hair growth. Fluridil, also known as topilutamide, is a topical antiandrogen used in the management of androgenetic alopecia, acting locally to inhibit androgen receptor activity in the scalp. 17-alpha-estradiol, or alfatradiol, is a topical estrogenic compound employed in certain cases of androgenetic alopecia, particularly in women, to modulate local androgen metabolism and support hair growth. These medications are selected based on the type of alopecia, patient characteristics, and treatment goals, with ongoing monitoring for efficacy and safety.
| Structure | Generic Name | CAS Registry Number | Molecular Formula | Molecular Weight |
|---|---|---|---|---|
 | ritlecitinib (Rec INN) | 1792180-81-4 | C15 H19 N5 O | 285.344 |
 | baricitinib (Rec INN; USAN) | 1187594-09-7 | C16 H17 N7 O2 S | 371.417 |
 | 883887-18-1 | C17 H16 O3 | 268.307 | |
 | dutasteride (Prop INNM; USAN) | 164656-23-9 | C27 H30 F6 N2 O2 | 528.53 |
 | finasteride (Rec INN; USAN; BAN) | 98319-26-7 | C23 H36 N2 O2 | 372.544 |
 | minoxidil (Rec INN; USAN; BAN) | 38304-91-5 | C9 H15 N5 O | 209.248 |
 | fluridil; topilutamide (Prop INN) | 260980-89-0 | C13 H11 F6 N3 O5 | 403.234 |
 | 17-alpha-estradiol; alfatradiol (Rec INN); epiestradiol | 57-91-0 | C18 H24 O2 | 272.382 |
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