Androgenic alopecia is by far the most common form of alopecia in men and women.
The development and occurrence of AGA depend on genetic predisposition and an interaction of endocrine factors.
AGA involves both genetic and hormonal factors.
Different gene loci have been linked to the development of AG
After puberty, androgen triggers a series of events within theses genetically programmed hair follicles, predominately in fronto-parietal scalp area, that transform terminal to miniaturized follicles.
In AGA, hair cycle dynamic change. The time between shedding of hair and anagen regrowth become longer, leading to a reduction of present hair on the scalp.
The Expression of Insulin-like growth factor(IGF)-1, in dermal papilla, may play important role in the development of pattern baldness.
A gene locus on chromosome 12 (12q22-q23) may be responsible for male pattern baldness. More recent study shows that 17q21.31 may be locus for early onset AGA.
The CYP17 gene on chromosome 10q24.3 was held responsible for female pattern baldness.
Ellis shows there is no role of 5µ-reductase isoenzymes in the causation of male pattern baldness.
In balding scalp, higher expression of the androgen receptor gene was found which is located at band q12 in the X chromosome.
The involvement of the X chromosome in the development of AGA stresses the importance of the maternal line in inheritance.
All enzymes can be located in the sebaceous gland and different parts of the hair follicle of the scalp skin. Therefore, pilosebaceous unit has the potential to mediate androgetic action without relying on elevated systemic levels or production of testosterone or DHT.
Increased level of AROMATASE (Detoxifying by removal of excess androgens) in females explain the difference in male and female patterns of balding and sparing of the frontal hairline.
5µ-reductase plays a key role in AGA.Two 5µ-reductase isoenzymes are found in dermal papilla cells of beard and scalp follicles. In the balding scalp, a predominance of 5µ-reductase isotype 1 can be found.
Hair loss, medically termed alopecia, can result from a multitude of factors ranging from genetic predisposition to nutritional deficiencies. The causes of hair loss can broadly be categorized into pattern and non-pattern hair loss, hormonal imbalances, nutritional deficiencies, lifestyle factors, medical conditions, and scarring alopecia. Understanding these underlying causes is crucial for proper diagnosis and treatment.
Androgenic Alopecia (Pattern Hair Loss)
Androgenic alopecia (AGA), also known as pattern hair loss, is the most prevalent form of hair loss in both men and women. It is characterized by a progressive thinning of the hair, typically following a specific pattern.
Pathogenesis of Androgenic Alopecia
AGA involves both genetic and hormonal factors. After puberty, androgens, particularly dihydrotestosterone (DHT), trigger a series of events within genetically predisposed hair follicles. These events primarily affect the follicles in the fronto-parietal scalp area, leading to the transformation of terminal (thick and pigmented) hair follicles into miniaturized (thin and short) ones.
Genetic Factors
– Polygenic Inheritance: The risk of developing AGA increases significantly with a positive family history. It is inherited in a polygenic manner, meaning multiple genes contribute to its development.
– Gene Loci: Specific gene loci, such as those on chromosome 12 (12q22-q23) for male pattern baldness and chromosome 17q21.31 for early onset AGA, have been identified. The CYP17 gene on chromosome 10q24.3 is implicated in female pattern baldness.
– Insulin-like Growth Factor (IGF-1): The expression of IGF-1 in the dermal papilla may play a significant role in the development of pattern baldness.
– X Chromosome Involvement: Higher expression of the androgen receptor gene on the X chromosome (band q12) suggests maternal line inheritance plays an important role.
Hormonal Factors
– Androgen Receptors and 5α-Reductase: Increased activity of 5α-reductase, particularly isotype 1 in the balding scalp, leads to higher conversion of testosterone to DHT, which is more potent in shrinking hair follicles.
– Aromatase Activity: Higher levels of aromatase in females, which detoxifies androgens, explain the different patterns of hair loss between men and women and the preservation of the frontal hairline in women.
Male Pattern Baldness (MPB)
– Prevalence: More than 90% of hair loss cases in men are due to AGA, affecting about 6 out of 10 men.
– Onset and Progression: AGA can begin as early as age 12, with most cases starting between ages 15 and 25. The progression is gradual, often reaching maximum severity by the forties.
– Family History: Strong family history is present in most cases, though about 12% may have no family history.
– 5α-Reductase Isoenzymes: Two isoenzymes are found in hair follicles, with isotype 1 predominating in balding scalp.
Telogen Effluvium (Non-Pattern Hair Loss – Generalized)
Telogen effluvium is a form of diffuse hair loss that occurs when a significant number of hair follicles enter the telogen (resting) phase prematurely. It can be triggered by various factors, including:
– Stress and Anxiety: Emotional or physical stress can push hair follicles into the telogen phase.
– Dieting and Nutritional Deficiencies: Rapid weight loss, crash diets, or deficiencies in vitamins (A, C, E), minerals (zinc, selenium, copper), and low serum protein levels can lead to telogen effluvium.
– Hormonal Changes: Thyroid imbalances (hyperthyroidism, hypothyroidism, hypoparathyroidism) and postpartum hormonal shifts can cause this condition.
– Medical Conditions: Diabetes mellitus and hypopituitarism can disrupt the hair growth cycle.
– Medications: Certain drugs can induce hair loss as a side effect.
– Acute Illness or Surgery: Acute blood loss, general anesthesia, and severe infections can lead to temporary hair loss.
Common Scarring Alopecia
Scarring alopecia, or cicatricial alopecia, involves the destruction of hair follicles, replaced by scar tissue, and permanent hair loss. Common causes include:
– Discoid Lupus Erythematosus: An autoimmune condition that affects the skin, leading to inflammation and scarring of hair follicles.
– Lichen Planopilaris: A rare inflammatory condition that causes patchy hair loss and scarring.
– Severe Infections: Fungal, viral, and bacterial infections can damage hair follicles irreversibly.
– Trauma or Burns: Physical trauma or burns to the scalp can destroy hair follicles, leading to scarring and permanent hair loss.
Additional Causes of Hair Loss
Drugs: Certain medications, including chemotherapy drugs, antidepressants, and blood thinners, can cause hair loss.
Weight Loss: Rapid or significant weight loss can stress the body, leading to hair shedding.
Acute Blood Loss: Sudden blood loss can disrupt the hair growth cycle.
General Anesthesia: Undergoing general anesthesia can lead to temporary hair loss, which may become chronic in some cases.
Post-Partum: Hormonal changes after childbirth can cause temporary hair shedding.
Conclusion
Hair loss can result from a wide array of causes, including genetic predispositions, hormonal imbalances, nutritional deficiencies, lifestyle factors, medical conditions, and scarring from infections or trauma. Androgenic alopecia, or pattern hair loss, is the most common form, driven by a combination of genetic and hormonal factors. Non-pattern hair loss, such as telogen effluvium, can be triggered by stress, nutritional deficiencies, and medical conditions. Understanding these diverse causes is essential for effective diagnosis and treatment, allowing for tailored interventions to address the specific underlying factors contributing to hair loss.
Book an Appointment