Hormonal Effects on Hair Follicles

Area of Science:

• Endocrinology
• Dermatology
• Hair Biology

Background:

• Hair follicle structure and the hair cycle are intricately regulated by hormonal signals.
• Androgens, including testosterone (T) and dihydrotestosterone (DHT), are primary drivers of terminal hair growth in specific body areas.
• These hormones convert vellus hairs into terminal hairs by acting on androgen receptors in dermal papilla cells.

Purpose of the Study:

• To provide a comprehensive review of the effects of various hormones on hair follicle biology.
• To elucidate the mechanisms by which androgens, estrogens, progesterone, and prolactin influence hair growth.
• To synthesize current research on hormonal regulation of the hair cycle.

Main Methods:

• Literature review of existing analyses and studies on hormonal effects on hair follicles.
• Synthesis of data on hormone-receptor interactions and enzymatic conversions within the hair follicle.
• Analysis of research investigating the roles of testosterone, DHT, estradiol, progesterone, and prolactin.

Main Results:

• Androgens (T, DHT) are key to terminal hair growth, acting via androgen receptors and often requiring 5-alpha reductase for conversion.
• Estradiol influences hair follicle cycling through estrogen receptors and aromatase activity.
• Progesterone can inhibit testosterone to DHT conversion, and prolactin (PRL) has also been detected in human scalp skin, suggesting a role in hair growth.

Conclusions:

• Hormonal fluctuations profoundly affect hair follicle dynamics and hair characteristics.
• Androgens, estrogens, progesterone, and prolactin each exert distinct influences on hair growth and the hair cycle.
• Understanding these hormonal mechanisms is essential for addressing hair-related conditions.