For how we live.
In 221 male childhood-cancer survivors, FSH levels during puberty tracked adult testicular function. Radiotherapy damage persisted into adulthood, while alkylating-chemotherapy effects often recovered.
Injecting one sperm into each egg was meant for severe male-factor cases, yet clinics now use it widely. Pooling six randomised trials found no live-birth advantage over standard IVF when sperm is not the problem.
It anchors every male-infertility evaluation, but its reference numbers come from a few thousand fertile men — and a normal result never rules fertility in or out.
A study of 3,932 athletes found cyclists had no worse erectile or urinary function than swimmers and runners. But heavy saddle time is tied to genital numbness, and men logging 5+ hours a week showed lower sperm counts.
A Cochrane review of 48 trials found treatment may lift pregnancy rates from about 21% to 22–48%, but couldn't confirm a live-birth benefit. Microsurgery had the fewest recurrences.
Low testosterone is a symptom, not a diagnosis. It splits into testicular and pituitary causes — and Klinefelter syndrome, the commonest genetic cause, is found in only about a quarter of the men who have it.
A daily testosterone-and-progestin gel is in a 52-week efficacy trial in 462 couples. A non-hormonal pill cleared its first safety study in 16 men. Neither is approved.
Exogenous testosterone switches off the body's own signals to the testes. In a male-contraceptive trial, 95.9 per 100 men fell to near-zero sperm counts. The effect is usually, but not always, reversible.
Consumer kits reliably estimate sperm concentration, and a smartphone assay matched lab classification ~98% of the time. But a normal count can't rule out the motility, shape and DNA problems a full analysis checks.
A meta-analysis of 14 studies and 7,465 men found little for the conventional semen parameters, and something more consistent for sperm DNA fragmentation.
Young men are chasing higher testosterone with 'natural boosters' and direct-to-consumer TRT. The supplements are largely unproven; unnecessary therapy carries real costs to fertility.
The scrotal-cooling theory is sound and the semen findings are real. A 2026 review found the prospective data show no difference in pregnancy outcomes by underwear type.
An umbrella review graded 249 effect sizes across 67 risk factors for male infertility. More than half were rated very low certainty — and the review contradicts its own table on one of them.
A 223-study meta-regression reports sperm concentration falling 51.6% since 1973. Two published critiques argue the method cannot support that reading. Both sides are peer-reviewed.