What are the differences between androgens, testosterone, and estrogen in females?

Androgens, Testosterone, and Estrogen in Females: Key Distinctions

Androgens are a class of steroid hormones that includes testosterone as a specific member, while estrogen represents a separate class of sex steroids—though androgens serve as obligatory precursors for estrogen synthesis in females. 1

Hierarchical Relationship

Androgens as a Hormone Class

• Androgens are NOT a single hormone but rather a category of steroid hormones that includes testosterone, dihydrotestosterone (DHT), and precursor molecules like DHEA and androstenedione 1
• DHEA and androstenedione are technically prohormones, not true androgens, because they do not directly bind to or activate the androgen receptor—they must first be converted to testosterone or DHT 1
• These prohormones can be converted to either testosterone/DHT (androgenic effects) OR to estrogens (estrogenic effects), making their tissue-specific actions complex 1

Testosterone's Specific Role

• Testosterone is both a hormone (acting directly in tissues like muscle) and a prohormone (converted to DHT in tissues like skin, labia majora, and clitoris) 1
• In female tissues where DHT is the active androgen, the DHT:testosterone ratio is approximately 2:1, compared to 0.3:1 in plasma 2
• Testosterone circulates in blood bound to proteins: approximately 65-75% bound to SHBG, 25-35% bound to albumin, and only 1-3% free (biologically active) 1

Estrogen's Distinct Identity

• Estrogens (primarily estradiol and estrone) are structurally derived FROM androgens via the enzyme aromatase, but function through completely different receptors and biological pathways 3
• This conversion means androgens are "obligatory precursors" of estrogens—you cannot make estrogen without first making androgens 4
• Despite this biosynthetic relationship, serum levels of androgens and estrogens track closely together in postmenopausal women, with highly significant correlations persisting even after adjusting for body mass index and insulin resistance 4

Production Sites in Females

Androgen/Testosterone Sources

• Ovaries and adrenal glands produce androgen precursors, which are then converted to testosterone in peripheral tissues 1, 2
• In premenopausal women, testosterone concentrations are approximately 15-fold lower than in males 5
• After menopause, there is a rapid decline in estrogen secretion but only a slow decrease in androgen secretion, creating a relative hyperandrogenic state 6

Estrogen Sources

• Primarily produced through aromatization of androgens in various tissues 3
• The estrogen-to-androgen ratio (particularly estradiol to free testosterone) may be more clinically relevant than absolute hormone levels 7

Clinical Measurement Challenges

Critical Assay Limitations

• Current testosterone assays lack adequate sensitivity and specificity for the low concentrations found in women, making clinical measurements unreliable 1
• The Endocrine Society explicitly recommends against making a diagnosis of androgen deficiency in women because there are neither well-defined clinical syndromes nor normative data across women's lifespans 1
• Mass spectrometry (MS/MS) methods are superior to immunoassays but still face challenges at female physiological ranges 1
• Direct immunoassays for free testosterone are seriously flawed and cannot be recommended 2

Intracrine Complexity

• Testosterone produced within target cells from precursors may never pass through plasma, making blood measurements incomplete indicators of androgenic activity 1
• Local tissue conversion and metabolism of androgens cannot be assessed with current methodology 1

Functional Differences in Females

Androgen/Testosterone Effects

• Androgen receptors are present throughout the female genitourinary system, with effects distinct from or complementary to estrogen 8
• Effects include maintenance of tissue structure, cell growth, collagen turnover, increased perfusion, and neurotransmitter synthesis 8
• No cutoff blood level can differentiate women with and without sexual dysfunction 9
• The Endocrine Society recommends against generalized testosterone use in women for infertility, sexual dysfunction (except HSDD in specific populations), cognitive dysfunction, cardiovascular health, metabolic dysfunction, bone health, or well-being due to inadequate indications and lack of long-term safety data 1, 2

Estrogen Effects

• Estrogen is protective against hair loss in women, and female pattern hair loss may be triggered by a low estrogen-to-androgen ratio rather than elevated absolute androgen levels 7
• Estrogen-only therapies producing periovulatory estradiol levels can increase sexual desire in postmenopausal women 10

Therapeutic Implications

• Testosterone therapy at physiological doses shows modest benefit only for hypoactive sexual desire disorder (HSDD) in surgically menopausal women 9, 2
• Supraphysiological (not physiological) testosterone doses enhance low-dose estrogen effectiveness for sexual desire, but the mechanism remains unknown 10
• No FDA-approved testosterone formulation exists for women in the United States due to lack of long-term safety data 2, 11

Key Clinical Pitfall

The concept of "male" and "female" hormones is an oversimplification—both androgens and estrogens regulate critical biological processes in both sexes through complex developmental and biological networks 3. In females specifically, the interplay between these hormone classes, their ratios, and local tissue metabolism determines physiological effects more than absolute circulating levels of any single hormone 1, 7.