The hormonal cascade in PCOS causes hirsutism through accelerated GnRH pulsatility, driving excessive LH secretion, which stimulates ovarian theca cells to overproduce androgens, particularly testosterone, while the FSH-granulosa cell axis becomes dysfunctional, leading to hyperandrogenism that acts directly on hair follicles to convert vellus hair to terminal hair in male-pattern distribution 1, 2, 3

The Hormonal Cascade

Accelerated GnRH pulsatility initiates the hormonal cascade, leading to disordered gonadotropin secretion, with the LH/FSH ratio typically exceeding 2:1, which is both diagnostically significant and mechanistically critical 1, 2, 3
Ovarian theca stromal cell hyperactivity occurs in direct response to elevated LH, causing these cells to massively overproduce androgens, particularly testosterone 1, 2, 3
FSH-granulosa cell axis hypofunction develops simultaneously, with FSH levels remaining relatively low or normal, preventing proper follicular maturation 1, 2, 3

The Metabolic Amplification Loop

Hyperinsulinemia directly stimulates ovarian theca cells to produce even more androgens, independent of LH stimulation, and suppresses hepatic production of sex hormone-binding globulin (SHBG), increasing the fraction of free testosterone circulating in the blood 3

Hyperandrogenism is present in 75% of PCOS cases and serves as both a diagnostic criterion and a central pathogenic driver 4, 5
The diagnosis of biochemical hyperandrogenism should prioritize total testosterone (TT) and free testosterone (FT) as first-line laboratory tests, with calculated free testosterone (cFT) assessed by equilibrium dialysis, ammonium sulfate precipitation, or calculated using free androgen index (FAI) 4, 5
LC-MS/MS methodology is superior to immunoassay for androgen measurement given its higher accuracy 4, 5

Weight gain is a major trigger for PCOS development and worsening hirsutism in genetically susceptible women, making lifestyle intervention essential 3
Certain medications, such as valproate, can exacerbate PCOS and trigger or worsen PCOS-like symptoms, including hirsutism 3, 6
Rapid-onset or severe hirsutism with virilization suggests an androgen-secreting tumor rather than PCOS and demands immediate aggressive workup 6, 3

SHBG concentrations are characteristically reduced in women with PCOS, making low SHBG both a diagnostic indicator of hyperandrogenism and a biomarker of metabolic dysfunction. [7][8]

In functional hypothalamic amenorrhea (FHA), SHBG levels are generally normal or elevated, which sharply contrasts with the low SHBG observed in PCOS. 9
FHA patients typically exhibit normal insulin sensitivity and low circulating insulin, whereas women with PCOS display insulin resistance even when they are not obese. 9
The lower SHBG seen in PCOS versus FHA is explained by insulin‑mediated inhibition of hepatic SHBG synthesis through the PI3K/AKT signaling pathway and associated lipogenic enzymes. 9

After bariatric surgery, women with PCOS experience a statistically significant rise in SHBG; however, the increase is approximately 32.7 nmol/L less than that observed in women without PCOS (mean difference = 32.72 nmol/L; 95 % CI 5.46–59.97; p = 0.02). This finding is derived from pooled data across multiple studies. [10][11]12
The attenuated SHBG response following substantial weight loss suggests that metabolic dysfunction persists in PCOS patients despite bariatric‑induced weight reduction. 10