What causes small testicles in a male of reproductive age after ejaculation?

Testicles Appearing Smaller After Ejaculation: Normal Physiological Response

The perception of smaller testicles after ejaculation is a normal physiological phenomenon related to temporary changes in testicular position, cremasteric muscle contraction, and scrotal skin changes—not actual testicular atrophy or pathology. 1

Understanding the Normal Physiology

What Happens During and After Ejaculation

• The cremasteric muscle contracts during sexual arousal and ejaculation, pulling the testicles closer to the body, which can make them appear smaller and feel firmer 1
• The scrotal skin tightens during arousal and gradually relaxes after ejaculation, contributing to perceived size changes 1
• These changes are temporary and reversible, typically resolving within minutes to hours after ejaculation 1

Actual Testicular Volume Does Not Change

• True testicular volume (measured by ultrasound or orchidometer) does not decrease after ejaculation—only the position and scrotal skin tension change 2
• The testicles produce sperm continuously through spermatogenesis, which is not affected by individual ejaculatory events 3
• Semen components come primarily from the prostate, seminal vesicles, and bulbourethral glands—not from testicular volume itself 1

When to Be Concerned: Red Flags That Require Evaluation

Persistent Small Testicular Size (Not Related to Ejaculation)

• Testicular volumes consistently less than 12 ml are considered atrophic and warrant investigation, particularly when associated with infertility concerns 4, 2
• Testicular atrophy is strongly associated with impaired spermatogenesis when accompanied by elevated FSH levels above 7.6 IU/L 3
• Size discrepancy between testes greater than 2 ml or 20% warrants ultrasound evaluation to exclude pathology 2

Symptoms Requiring Urgent Evaluation

• Sudden onset of testicular pain, swelling, or firmness (concern for testicular torsion requiring emergency surgery within 6 hours) 5
• Palpable testicular mass or nodule (concern for testicular cancer, which has higher incidence in men with infertility) 4
• Progressive testicular atrophy over weeks to months (concern for primary testicular failure) 2

Proper Testicular Assessment

Measurement Technique

• Use a Prader orchidometer for clinical volume estimation, which is cost-effective and correlates well with ultrasound in most cases 4
• Scrotal ultrasound is indicated when physical examination is difficult due to large hydrocele, inguinal testis, epididymal enlargement, thickened scrotal skin, or when the epididymis appears large compared to testicular volume 4
• Calculate volume using the Lambert formula (Length × Width × Height × 0.71) for accurate ultrasound measurements, as the traditional ellipsoid formula (0.52 coefficient) systematically underestimates volume by 20-30% 2

Normal Reference Values

• Normal adult testicular volume ranges from 15-18 ml, with volumes below 12 ml considered atrophic 2
• Testicular length of approximately 4 cm corresponds to a volume of 15-18 ml 2
• Mean testicular size strongly correlates with total sperm count and sperm concentration 2

Common Pitfalls to Avoid

• Do not confuse temporary post-ejaculatory changes in testicular position and scrotal skin tension with true testicular atrophy 2, 1
• Avoid measuring testicular size immediately after ejaculation when cremasteric contraction is maximal—wait several hours for accurate assessment 1
• Do not assume normal testicular size guarantees normal fertility, as semen analysis is required to assess actual sperm production 2
• Never start exogenous testosterone therapy if fertility is desired, as it suppresses FSH and LH through negative feedback, causing azoospermia that can take months to years to recover 6

When Fertility Evaluation Is Indicated

• History of cryptorchidism (undescended testicles), which substantially increases cancer risk and affects fertility 4, 2
• Inability to conceive after 12 months of regular unprotected intercourse 4
• Consistently small testicular volume (<12 ml) on physical examination 2
• Abnormal semen analysis parameters (concentration <15 million/ml, motility <40%, morphology <4% normal forms) 4