Low Testosterone Does NOT Directly Affect Semen Color, Thickness, or Volume in Most Men
Low testosterone itself does not directly regulate semen color, thickness, or volume—these characteristics are primarily determined by dihydrotestosterone (DHT) and the secretory function of the prostate and seminal vesicles, not testosterone. 1, 2
The DHT Connection: What Actually Controls Semen Characteristics
- Dihydrotestosterone (DHT), not testosterone, is the primary androgen regulating semen volume and viscosity through its effects on prostate and seminal vesicle development and function 1, 2
- Men with 5-alpha-reductase-2 deficiency (who cannot convert testosterone to DHT) demonstrate extremely low semen volumes (range <0.05 to 1.0 mL), increased viscosity, and poor liquefaction despite having normal testosterone levels 2
- Finasteride 5 mg/day (which blocks DHT production) is specifically associated with reduced semen volume, further confirming DHT's role rather than testosterone's role 1
When Low Testosterone DOES Affect Semen: The Exogenous Testosterone Trap
- Exogenous testosterone supplementation suppresses spermatogenesis and can cause oligospermia or azoospermia through suppression of gonadotropin secretion, which is a critical pitfall to avoid 1
- The NCCN guidelines explicitly warn that exogenous testosterone should never be prescribed to men trying to conceive because it causes short-term suppression of sperm production 1
- Testosterone replacement therapy should be avoided in men desiring fertility as it suppresses spermatogenesis 3
What Low Endogenous Testosterone Actually Does (and Doesn't Do)
- In a large study of 853 male partners of infertile couples with total sperm count >5 million, low total testosterone (<264 ng/dL) showed no significant effect on semen volume, sperm count, motility, or morphology compared to men with normal testosterone 4
- Multivariable regression analysis confirmed that low testosterone and free testosterone levels had no significant effect on semen parameters (p = 0.53,0.8,0.3,0.2 for various parameters) 4
- Mean testosterone levels are lower in men with diabetes compared to age-matched controls, but obesity is a major confounder rather than a direct testosterone effect 5
Clinical Implications for Evaluation
- When evaluating low semen volume with normal testosterone levels, consider ejaculatory duct obstruction or congenital bilateral absence of vas deferens (CBAVD) rather than attributing it to testosterone 6, 3
- Acidic semen (pH <7.0) with volume <1.4-1.5 mL strongly suggests ejaculatory duct obstruction or CBAVD, not testosterone deficiency 6
- Post-ejaculatory urinalysis is recommended when volume <1 mL (except in bilateral vasal agenesis or hypogonadism) to diagnose retrograde ejaculation 6
Other Factors That Actually Influence Semen Characteristics
- Hydration status and ejaculatory frequency can influence semen volume 1
- Obesity and metabolic factors are associated with decreased ejaculate volume through mechanisms unrelated to testosterone 1
- Testicular volume correlates with sperm parameters, but this reflects overall testicular function rather than testosterone levels specifically 7
The Bottom Line for Clinical Practice
Low endogenous testosterone does not change semen color, thickness, or volume in the vast majority of men. The confusion arises because: (1) DHT, not testosterone, regulates these characteristics; (2) exogenous testosterone supplementation does affect semen by suppressing sperm production entirely; and (3) conditions causing low testosterone may coincidentally affect semen through other mechanisms. When you encounter abnormal semen characteristics, look for structural abnormalities, DHT-related issues, or other metabolic factors rather than blaming testosterone levels alone. 1, 4, 2