madman
Super Moderator
Hormonal Effects on Hair Follicles
Monika Grymowicz, Ewa Rudnicka, Agnieszka Podfigurna, Paulina Napierala, Roman Smolarczyk, Katarzyna Smolarczyk and Blazej Meczekalsk
Abstract:
The hair cycle and hair follicle structure are highly affected by various hormones. Androgens—such as testosterone (T); dihydrotestosterone (DHT); and their prohormones, dehydroepiandrosterone sulfate (DHEAS) and androstendione (A)—are the key factors in terminal hair growth. They act on sex-specific areas of the body, converting small, straight, fair vellus hairs into larger darker terminal hairs. They bind to intracellular androgen receptors in the dermal papilla cells of the hair follicle. The majority of hair follicles also require the intracellular enzyme 5-alpha reductase to convert testosterone into DHT. Apart from androgens, the role of other hormones is also currently being researched—e.g., estradiol can significantly alter the hair follicle growth and cycle by binding to estrogen receptors and influencing aromatase activity, which is responsible for converting androgen into estrogen (E2). Progesterone, at the level of the hair follicle, decreases the conversion of testosterone into DHT. The influence of prolactin (PRL) on hair growth has also been intensively investigated, and PRL and PRL receptors were detected in human scalp skin. Our review includes results from many analyses and provides a comprehensive up-to-date understanding of the subject of the effects of hormonal changes on the hair follicle.
1. Introduction
The hair cycle, as well as the structure of the hair follicle, are highly affected by various hormones. In particular, the impact of androgens has been studied and exhaustively described in previous studies [1,2]. Androgens influence hair follicles depending on the hair location on the body. The main action of androgen on the hair follicle is referred to as binding to androgen receptors in dermal papilla cells. Research studies also provide information about the locations of androgen production related to enzymes in the hair structure. Apart from androgens, the pathogenic role of other hormones is also currently being researched. In our review, the results from many analyses have been included. This review provides a comprehensive up-to-date understanding of the subject of the hormonal effects on the hair follicle. This review also highlights the significant progress in research that has been made in recent years on the effects of hormonal changes on hair at different stages of the life of women [3].
2. Hair Follicle Biology
2.1. Structure of the Hair Follicle
2.2. The Hair Follicle Cycle
3. Endocrine Regulations of the Hair Follicle
3.1. Androgens
3.1.1. General Information
Androgens are sex steroid hormones with specific locations of production. The sources of androgen are the adrenal glands, the gonads (ovaries, testes), the brain, and the placenta in pregnant women. Androgens exert their action through intracellular receptors [3]. The adrenal glands are the source of DHEA and DHEA-S, which are relatively weak androgens. The production of testosterone is limited to the testes (from puberty) in males and to the ovaries and the adrenal cortex in women of reproductive age. In females, testosterone comes in significant amounts from androstenedione. Androstenedione production takes place in equal amounts in the adrenal cortex and ovaries in females. In males, androstenedione is produced in small amounts by the testes [7].
Dihydrotestosterone is an endogenous androgen. The enzyme 5-alpha reductase is responsible for the transformation of testosterone to dihydrotestosterone at the level of tissues such as the skin, hair follicles, the prostate gland, the seminal vesicles, the liver, and the brain. Androgens can be also produced at the skin level, both de novo from cholesterol and from adrenal precursors (DHEA) [8].
3.1.2. Androgen Receptor
Androgens act through an intracellular androgen receptor in the cells of the hair follicle [9]. Androgen receptors are located in human hair follicles in the dermal papilla cells. Some reports also show the expression in the outer root sheath. They are not found in the hair bulb or the bulge [10]. They are activated by the binding of androgens—testosterone and the more potent dihydrotestosterone. The main action of androgen on the hair follicle is related to binding to androgen receptors in dermal papilla cells [11]. It causes an alteration in gene expression. Insulin-like growth factor (IGF-1) is the key signal responsible for hair follicle growth stimulation. By contrast, transforming growth factor-beta (TGF-beta) is regarded as the key signal responsible for hair follicle growth inhibition [2].
3.1.3. Androgen Action
The role of androgen on hair growth is undeniable. However, the influence of androgen on hair follicles depends on the hair location on the body. During puberty, an important increase in serum androgen levels is observed, and vellus hair in the pubic and axillary regions under androgen influence is transformed into terminal hairs [2]. Hair follicles in such body regions as the face, the axilla, the pubis, and the chest are subject to the stimulatory effect of androgens. The hair follicles located in the eyelashes are not under the influence of androgen. By contrast, androgens exert an inhibitory effect on the hair follicles in the region of the scalp [1]. Androgen-metabolizing enzymes can be identified in normal hair follicle locations. These enzymes play an essential role at the level of the hair follicle. Aromatase, 17 beta-HSD, and 5-alpha reductase (type I and II) are located within the outer root sheath. Aromatase and 5-alpha reductase (type I and II) are located within the inner sheath. The dermal papilla is the location of the action of enzymes such as aromatase, 17 beta-HSD, 5-alpha reductase (type II), and sulphatase. Regarding the sebaceous duct, 5-alpha reductase, and the sebaceous gland, two important enzymes can be identified: aromatase and 5-alpha reductase (type I) [1]. Despite important advances in our knowledge, there are still many aspects of the influence of androgen on the hair follicle which are unclear, and further research studies are required.
3.2. Sex Hormones
3.2.1. Estradiol
3.2.2. Progesterone
3.3 Prolactin
3.4. Thyroid Gland Hormones
3.5. Melatonin
3.6. Other Hormones
3.6.1. CRH
3.6.2. ACTH
3.6.3. CORTISOL
3.6.4. TRH
3.6.5. GALANIN
4. Hormonal Effects on Hair at Different Stages of the Life of Women
4.1. Reproductive Age
4.2. Pregnancy
4.3. Menopause
5. Conclusions
The skin can be considered to be an endocrine organ because it has been shown that it is able to synthesize a range of diverse hormones with the expression of the associated hormone receptors [74,75]. Although many hormonal paths and influences on hair growth have already been described in the literature, further studies on the full impact of hormonal regulation on hair growth need to be conducted.
Monika Grymowicz, Ewa Rudnicka, Agnieszka Podfigurna, Paulina Napierala, Roman Smolarczyk, Katarzyna Smolarczyk and Blazej Meczekalsk
Abstract:
The hair cycle and hair follicle structure are highly affected by various hormones. Androgens—such as testosterone (T); dihydrotestosterone (DHT); and their prohormones, dehydroepiandrosterone sulfate (DHEAS) and androstendione (A)—are the key factors in terminal hair growth. They act on sex-specific areas of the body, converting small, straight, fair vellus hairs into larger darker terminal hairs. They bind to intracellular androgen receptors in the dermal papilla cells of the hair follicle. The majority of hair follicles also require the intracellular enzyme 5-alpha reductase to convert testosterone into DHT. Apart from androgens, the role of other hormones is also currently being researched—e.g., estradiol can significantly alter the hair follicle growth and cycle by binding to estrogen receptors and influencing aromatase activity, which is responsible for converting androgen into estrogen (E2). Progesterone, at the level of the hair follicle, decreases the conversion of testosterone into DHT. The influence of prolactin (PRL) on hair growth has also been intensively investigated, and PRL and PRL receptors were detected in human scalp skin. Our review includes results from many analyses and provides a comprehensive up-to-date understanding of the subject of the effects of hormonal changes on the hair follicle.
1. Introduction
The hair cycle, as well as the structure of the hair follicle, are highly affected by various hormones. In particular, the impact of androgens has been studied and exhaustively described in previous studies [1,2]. Androgens influence hair follicles depending on the hair location on the body. The main action of androgen on the hair follicle is referred to as binding to androgen receptors in dermal papilla cells. Research studies also provide information about the locations of androgen production related to enzymes in the hair structure. Apart from androgens, the pathogenic role of other hormones is also currently being researched. In our review, the results from many analyses have been included. This review provides a comprehensive up-to-date understanding of the subject of the hormonal effects on the hair follicle. This review also highlights the significant progress in research that has been made in recent years on the effects of hormonal changes on hair at different stages of the life of women [3].
2. Hair Follicle Biology
2.1. Structure of the Hair Follicle
2.2. The Hair Follicle Cycle
3. Endocrine Regulations of the Hair Follicle
3.1. Androgens
3.1.1. General Information
Androgens are sex steroid hormones with specific locations of production. The sources of androgen are the adrenal glands, the gonads (ovaries, testes), the brain, and the placenta in pregnant women. Androgens exert their action through intracellular receptors [3]. The adrenal glands are the source of DHEA and DHEA-S, which are relatively weak androgens. The production of testosterone is limited to the testes (from puberty) in males and to the ovaries and the adrenal cortex in women of reproductive age. In females, testosterone comes in significant amounts from androstenedione. Androstenedione production takes place in equal amounts in the adrenal cortex and ovaries in females. In males, androstenedione is produced in small amounts by the testes [7].
Dihydrotestosterone is an endogenous androgen. The enzyme 5-alpha reductase is responsible for the transformation of testosterone to dihydrotestosterone at the level of tissues such as the skin, hair follicles, the prostate gland, the seminal vesicles, the liver, and the brain. Androgens can be also produced at the skin level, both de novo from cholesterol and from adrenal precursors (DHEA) [8].
3.1.2. Androgen Receptor
Androgens act through an intracellular androgen receptor in the cells of the hair follicle [9]. Androgen receptors are located in human hair follicles in the dermal papilla cells. Some reports also show the expression in the outer root sheath. They are not found in the hair bulb or the bulge [10]. They are activated by the binding of androgens—testosterone and the more potent dihydrotestosterone. The main action of androgen on the hair follicle is related to binding to androgen receptors in dermal papilla cells [11]. It causes an alteration in gene expression. Insulin-like growth factor (IGF-1) is the key signal responsible for hair follicle growth stimulation. By contrast, transforming growth factor-beta (TGF-beta) is regarded as the key signal responsible for hair follicle growth inhibition [2].
3.1.3. Androgen Action
The role of androgen on hair growth is undeniable. However, the influence of androgen on hair follicles depends on the hair location on the body. During puberty, an important increase in serum androgen levels is observed, and vellus hair in the pubic and axillary regions under androgen influence is transformed into terminal hairs [2]. Hair follicles in such body regions as the face, the axilla, the pubis, and the chest are subject to the stimulatory effect of androgens. The hair follicles located in the eyelashes are not under the influence of androgen. By contrast, androgens exert an inhibitory effect on the hair follicles in the region of the scalp [1]. Androgen-metabolizing enzymes can be identified in normal hair follicle locations. These enzymes play an essential role at the level of the hair follicle. Aromatase, 17 beta-HSD, and 5-alpha reductase (type I and II) are located within the outer root sheath. Aromatase and 5-alpha reductase (type I and II) are located within the inner sheath. The dermal papilla is the location of the action of enzymes such as aromatase, 17 beta-HSD, 5-alpha reductase (type II), and sulphatase. Regarding the sebaceous duct, 5-alpha reductase, and the sebaceous gland, two important enzymes can be identified: aromatase and 5-alpha reductase (type I) [1]. Despite important advances in our knowledge, there are still many aspects of the influence of androgen on the hair follicle which are unclear, and further research studies are required.
3.2. Sex Hormones
3.2.1. Estradiol
3.2.2. Progesterone
3.3 Prolactin
3.4. Thyroid Gland Hormones
3.5. Melatonin
3.6. Other Hormones
3.6.1. CRH
3.6.2. ACTH
3.6.3. CORTISOL
3.6.4. TRH
3.6.5. GALANIN
4. Hormonal Effects on Hair at Different Stages of the Life of Women
4.1. Reproductive Age
4.2. Pregnancy
4.3. Menopause
5. Conclusions
The skin can be considered to be an endocrine organ because it has been shown that it is able to synthesize a range of diverse hormones with the expression of the associated hormone receptors [74,75]. Although many hormonal paths and influences on hair growth have already been described in the literature, further studies on the full impact of hormonal regulation on hair growth need to be conducted.
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